[libvirt] [PATCH 0/4] Fix build with GCC 7
As always with new GCC major releases, we've tickled some new warnings. What's nice is that two of them identified genuine bugs in our code. I would push this as a build-breaker fix, but I wanted some visibility on the fourth patch before doing that, as it was not the usual type of quick fix. Daniel P. Berrange (4): Use explicit boolean comparison in OOM check libxl: fix empty string check for channel path qemu: add missing break in qemuDomainDeviceCalculatePCIConnectFlags Add ATTRIBUTE_FALLTHROUGH for switch cases without break src/conf/domain_conf.c | 7 +++++++ src/conf/network_conf.c | 3 ++- src/internal.h | 8 ++++++++ src/libxl/libxl_domain.c | 2 +- src/lxc/lxc_container.c | 2 +- src/network/bridge_driver.c | 6 ++++++ src/qemu/qemu_domain_address.c | 1 + src/util/viralloc.c | 2 +- tools/virsh-edit.c | 2 +- 9 files changed, 28 insertions(+), 5 deletions(-) -- 2.9.3
GCC 7 gets upset by if (!tmp && (size * count)) warning util/viralloc.c: In function 'virReallocN': util/viralloc.c:246:23: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context] if (!tmp && (size * count)) { ~~~~~~^~~~~~~~ Keep it happy by adding != 0 to the right hand expression so it realizes we really are wanting to treat the result of the arithmetic expression as a boolean Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/util/viralloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/util/viralloc.c b/src/util/viralloc.c index 812aa5b..81f99d9 100644 --- a/src/util/viralloc.c +++ b/src/util/viralloc.c @@ -243,7 +243,7 @@ int virReallocN(void *ptrptr, return -1; } tmp = realloc(*(void**)ptrptr, size * count); - if (!tmp && (size * count)) { + if (!tmp && ((size * count) != 0)) { if (report) virReportOOMErrorFull(domcode, filename, funcname, linenr); return -1; -- 2.9.3
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
GCC 7 gets upset by
if (!tmp && (size * count))
warning
util/viralloc.c: In function 'virReallocN': util/viralloc.c:246:23: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context] if (!tmp && (size * count)) { ~~~~~~^~~~~~~~
Keep it happy by adding != 0 to the right hand expression so it realizes we really are wanting to treat the result of the arithmetic expression as a boolean
ACK.
On 02/22/2017 06:52 PM, Daniel P. Berrange wrote:
GCC 7 gets upset by
if (!tmp && (size * count))
warning
util/viralloc.c: In function 'virReallocN': util/viralloc.c:246:23: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context] if (!tmp && (size * count)) { ~~~~~~^~~~~~~~
Keep it happy by adding != 0 to the right hand expression so it realizes we really are wanting to treat the result of the arithmetic expression as a boolean
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/util/viralloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/util/viralloc.c b/src/util/viralloc.c index 812aa5b..81f99d9 100644 --- a/src/util/viralloc.c +++ b/src/util/viralloc.c @@ -243,7 +243,7 @@ int virReallocN(void *ptrptr, return -1; } tmp = realloc(*(void**)ptrptr, size * count); - if (!tmp && (size * count)) { + if (!tmp && ((size * count) != 0)) { if (report) virReportOOMErrorFull(domcode, filename, funcname, linenr); return -1;
This is just stupid. I mean the warning, not your fix. Michal
On Thu, Feb 23, 2017 at 09:41:12AM +0100, Michal Privoznik wrote:
On 02/22/2017 06:52 PM, Daniel P. Berrange wrote:
GCC 7 gets upset by
if (!tmp && (size * count))
warning
util/viralloc.c: In function 'virReallocN': util/viralloc.c:246:23: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context] if (!tmp && (size * count)) { ~~~~~~^~~~~~~~
Keep it happy by adding != 0 to the right hand expression so it realizes we really are wanting to treat the result of the arithmetic expression as a boolean
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/util/viralloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/util/viralloc.c b/src/util/viralloc.c index 812aa5b..81f99d9 100644 --- a/src/util/viralloc.c +++ b/src/util/viralloc.c @@ -243,7 +243,7 @@ int virReallocN(void *ptrptr, return -1; } tmp = realloc(*(void**)ptrptr, size * count); - if (!tmp && (size * count)) { + if (!tmp && ((size * count) != 0)) { if (report) virReportOOMErrorFull(domcode, filename, funcname, linenr); return -1;
This is just stupid. I mean the warning, not your fix.
It is a warning that is certainly going to trigger a non-negligible number of false positives across various codebases, but I don't think it is stupid. The pattern it is looking for here with mixed integer and boolean operators has been a repeated source of bugs in software and a number of them have resulted in CVEs before when they've been mis-handling untrusted input validation or breaking crypto algorithms, etc. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
The libxl code was checking that a 'char *' was != '\0', instead of checking the first element in the string Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/libxl/libxl_domain.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c index 57ec661..ea28c93 100644 --- a/src/libxl/libxl_domain.c +++ b/src/libxl/libxl_domain.c @@ -1121,7 +1121,7 @@ libxlDomainCreateChannelPTY(virDomainDefPtr def, libxl_ctx *ctx) &channelinfo); if (!ret && channelinfo.u.pty.path && - channelinfo.u.pty.path != '\0') { + *channelinfo.u.pty.path != '\0') { VIR_FREE(chr->source->data.file.path); ignore_value(VIR_STRDUP(chr->source->data.file.path, channelinfo.u.pty.path)); -- 2.9.3
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
The libxl code was checking that a 'char *' was != '\0', instead of checking the first element in the string
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/libxl/libxl_domain.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c index 57ec661..ea28c93 100644 --- a/src/libxl/libxl_domain.c +++ b/src/libxl/libxl_domain.c @@ -1121,7 +1121,7 @@ libxlDomainCreateChannelPTY(virDomainDefPtr def, libxl_ctx *ctx) &channelinfo);
if (!ret && channelinfo.u.pty.path && - channelinfo.u.pty.path != '\0') { + *channelinfo.u.pty.path != '\0') { VIR_FREE(chr->source->data.file.path); ignore_value(VIR_STRDUP(chr->source->data.file.path, channelinfo.u.pty.path));
ACK.
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath. Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/qemu/qemu_domain_address.c | 1 + 1 file changed, 1 insertion(+) diff --git a/src/qemu/qemu_domain_address.c b/src/qemu/qemu_domain_address.c index 5b75044..27ca010 100644 --- a/src/qemu/qemu_domain_address.c +++ b/src/qemu/qemu_domain_address.c @@ -553,6 +553,7 @@ qemuDomainDeviceCalculatePCIConnectFlags(virDomainDeviceDefPtr dev, return pciFlags; } } + break; case VIR_DOMAIN_DEVICE_FS: /* the only type of filesystem so far is virtio-9p-pci */ -- 2.9.3
On Wed, 2017-02-22 at 17:52 +0000, Daniel P. Berrange wrote:
@@ -553,6 +553,7 @@ qemuDomainDeviceCalculatePCIConnectFlags(virDomainDeviceDefPtr dev, return pciFlags; } } + break; case VIR_DOMAIN_DEVICE_FS: /* the only type of filesystem so far is virtio-9p-pci */
I don't get this: all switches, whether top-level with respect to the function or not, provide full coverage of the respective enum, and inside those switches all cases return explicitly, so none of them can really fall through. How is it that only this one is bothering the compiler? -- Andrea Bolognani / Red Hat / Virtualization
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath.
Actually that's not true. Every codepath of the preceding case ends with a "return blah". This is true for the entire function - every case of every switch in the function ends with "return blah". The entire purpose of the function is to determine the flags value, and there are no resources that need cleaning up before returning, so as soon as the value is determined, it immediately returns. I suppose it could be rewritten to change all of those into "ret = blah; break;", then "return ret;" at the end, but it seemed safer to return immediately than to trust that no new code would be added later in the function (and also it's more compact) I wonder if this is just a more extreme case of the logic in whatever check necessitated that I add an extra "return 0" at the very end of the function. (that happens even in gcc 6.x; at an earlier point when the function was simpler, that wasn't needed, but after some additions it started producing the "control reaches end of function that requires a return value" or whatever that warning is, and the only way to eliminate it was with the extra return 0.) If adding the break shuts up the warning, then I guess ACK, but it would probably be better if 1) gcc fixed their incorrect warning, or 2) we switched the entire function to use the less-compact "ret = blah; break;" style instead of returning directly, so there wasn't a single stray break sitting in the middle.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/qemu/qemu_domain_address.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/src/qemu/qemu_domain_address.c b/src/qemu/qemu_domain_address.c index 5b75044..27ca010 100644 --- a/src/qemu/qemu_domain_address.c +++ b/src/qemu/qemu_domain_address.c @@ -553,6 +553,7 @@ qemuDomainDeviceCalculatePCIConnectFlags(virDomainDeviceDefPtr dev, return pciFlags; } } + break;
case VIR_DOMAIN_DEVICE_FS: /* the only type of filesystem so far is virtio-9p-pci */
On Wed, Feb 22, 2017 at 02:44:01PM -0500, Laine Stump wrote:
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath.
Actually that's not true. Every codepath of the preceding case ends with a "return blah". This is true for the entire function - every case of every switch in the function ends with "return blah". The entire purpose of the function is to determine the flags value, and there are no resources that need cleaning up before returning, so as soon as the value is determined, it immediately returns.
I suppose it could be rewritten to change all of those into "ret = blah; break;", then "return ret;" at the end, but it seemed safer to return immediately than to trust that no new code would be added later in the function (and also it's more compact)
I wonder if this is just a more extreme case of the logic in whatever check necessitated that I add an extra "return 0" at the very end of the function. (that happens even in gcc 6.x; at an earlier point when the function was simpler, that wasn't needed, but after some additions it started producing the "control reaches end of function that requires a return value" or whatever that warning is, and the only way to eliminate it was with the extra return 0.)
If adding the break shuts up the warning, then I guess ACK, but it would probably be better if 1) gcc fixed their incorrect warning, or 2) we switched the entire function to use the less-compact "ret = blah; break;" style instead of returning directly, so there wasn't a single stray break sitting in the middle.
I would say NACK since 1) is the correct option (at least for now), there is no reason for adding more lines of code that don't make sense just because of a compiler version that was not released yet, or does not even have a release plan yet.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/qemu/qemu_domain_address.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/src/qemu/qemu_domain_address.c b/src/qemu/qemu_domain_address.c index 5b75044..27ca010 100644 --- a/src/qemu/qemu_domain_address.c +++ b/src/qemu/qemu_domain_address.c @@ -553,6 +553,7 @@ qemuDomainDeviceCalculatePCIConnectFlags(virDomainDeviceDefPtr dev, return pciFlags; } } + break;
case VIR_DOMAIN_DEVICE_FS: /* the only type of filesystem so far is virtio-9p-pci */
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On Wed, Feb 22, 2017 at 09:19:15PM +0100, Martin Kletzander wrote:
On Wed, Feb 22, 2017 at 02:44:01PM -0500, Laine Stump wrote:
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath.
Actually that's not true. Every codepath of the preceding case ends with a "return blah". This is true for the entire function - every case of every switch in the function ends with "return blah". The entire purpose of the function is to determine the flags value, and there are no resources that need cleaning up before returning, so as soon as the value is determined, it immediately returns.
I suppose it could be rewritten to change all of those into "ret = blah; break;", then "return ret;" at the end, but it seemed safer to return immediately than to trust that no new code would be added later in the function (and also it's more compact)
I wonder if this is just a more extreme case of the logic in whatever check necessitated that I add an extra "return 0" at the very end of the function. (that happens even in gcc 6.x; at an earlier point when the function was simpler, that wasn't needed, but after some additions it started producing the "control reaches end of function that requires a return value" or whatever that warning is, and the only way to eliminate it was with the extra return 0.)
If adding the break shuts up the warning, then I guess ACK, but it would probably be better if 1) gcc fixed their incorrect warning, or 2) we switched the entire function to use the less-compact "ret = blah; break;" style instead of returning directly, so there wasn't a single stray break sitting in the middle.
I would say NACK since 1) is the correct option (at least for now), there is no reason for adding more lines of code that don't make sense just because of a compiler version that was not released yet, or does not even have a release plan yet.
GCC 7 *is* released - and has even had a bug fix release too, so ignoring this is not an option. In any case, as Eric mentions this is a genuine bug in our code since we can fall out of the inner switch if the input variable contains a value that doesn't map to an named enum value. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
On Thu, Feb 23, 2017 at 09:48:48AM +0000, Daniel P. Berrange wrote:
On Wed, Feb 22, 2017 at 09:19:15PM +0100, Martin Kletzander wrote:
On Wed, Feb 22, 2017 at 02:44:01PM -0500, Laine Stump wrote:
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath.
Actually that's not true. Every codepath of the preceding case ends with a "return blah". This is true for the entire function - every case of every switch in the function ends with "return blah". The entire purpose of the function is to determine the flags value, and there are no resources that need cleaning up before returning, so as soon as the value is determined, it immediately returns.
I suppose it could be rewritten to change all of those into "ret = blah; break;", then "return ret;" at the end, but it seemed safer to return immediately than to trust that no new code would be added later in the function (and also it's more compact)
I wonder if this is just a more extreme case of the logic in whatever check necessitated that I add an extra "return 0" at the very end of the function. (that happens even in gcc 6.x; at an earlier point when the function was simpler, that wasn't needed, but after some additions it started producing the "control reaches end of function that requires a return value" or whatever that warning is, and the only way to eliminate it was with the extra return 0.)
If adding the break shuts up the warning, then I guess ACK, but it would probably be better if 1) gcc fixed their incorrect warning, or 2) we switched the entire function to use the less-compact "ret = blah; break;" style instead of returning directly, so there wasn't a single stray break sitting in the middle.
I would say NACK since 1) is the correct option (at least for now), there is no reason for adding more lines of code that don't make sense just because of a compiler version that was not released yet, or does not even have a release plan yet.
GCC 7 *is* released - and has even had a bug fix release too, so ignoring this is not an option. In any case, as Eric mentions this is a genuine bug in our code since we can fall out of the inner switch if the input variable contains a value that doesn't map to an named enum value.
Where did you get the package/tarball? I don't see anything in the release page [1]. On the other hand, when I checked it yesterday, I looked and the development timeline [2] and I thought it's 2016 apparently because when I see the dates now it makes sense that the release should be around the corner. Anyway, even if they did not update the release page, on snapshot ftp [3] there is not even a release candidate. I remember others not being happy when we were doing workarounds for packages that downstream distros just decided to package out of VCS or snapshots. I don't feel it's right either and I thought you're on that side as well. Anyway, if it really was released, I am OK with this going in. Martin [1] https://gcc.gnu.org/releases.html [2] https://gcc.gnu.org/develop.html#timeline [3] ftp://gcc.gnu.org/pub/gcc/snapshots/
Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
On Thu, Feb 23, 2017 at 11:38:40AM +0100, Martin Kletzander wrote:
On Thu, Feb 23, 2017 at 09:48:48AM +0000, Daniel P. Berrange wrote:
On Wed, Feb 22, 2017 at 09:19:15PM +0100, Martin Kletzander wrote:
On Wed, Feb 22, 2017 at 02:44:01PM -0500, Laine Stump wrote:
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath.
Actually that's not true. Every codepath of the preceding case ends with a "return blah". This is true for the entire function - every case of every switch in the function ends with "return blah". The entire purpose of the function is to determine the flags value, and there are no resources that need cleaning up before returning, so as soon as the value is determined, it immediately returns.
I suppose it could be rewritten to change all of those into "ret = blah; break;", then "return ret;" at the end, but it seemed safer to return immediately than to trust that no new code would be added later in the function (and also it's more compact)
I wonder if this is just a more extreme case of the logic in whatever check necessitated that I add an extra "return 0" at the very end of the function. (that happens even in gcc 6.x; at an earlier point when the function was simpler, that wasn't needed, but after some additions it started producing the "control reaches end of function that requires a return value" or whatever that warning is, and the only way to eliminate it was with the extra return 0.)
If adding the break shuts up the warning, then I guess ACK, but it would probably be better if 1) gcc fixed their incorrect warning, or 2) we switched the entire function to use the less-compact "ret = blah; break;" style instead of returning directly, so there wasn't a single stray break sitting in the middle.
I would say NACK since 1) is the correct option (at least for now), there is no reason for adding more lines of code that don't make sense just because of a compiler version that was not released yet, or does not even have a release plan yet.
GCC 7 *is* released - and has even had a bug fix release too, so ignoring this is not an option. In any case, as Eric mentions this is a genuine bug in our code since we can fall out of the inner switch if the input variable contains a value that doesn't map to an named enum value.
Where did you get the package/tarball? I don't see anything in the release page [1]. On the other hand, when I checked it yesterday, I looked and the development timeline [2] and I thought it's 2016 apparently because when I see the dates now it makes sense that the release should be around the corner. Anyway, even if they did not update the release page, on snapshot ftp [3] there is not even a release candidate.
I didn't use any tarball - just what's in Fedora which is gcc-7.0.1-0.9.fc26.x86_64 Fedora dist-git says the tarball is gcc-7.0.1-20170219.tar.bz2 Odd that its not on the download page though as that's a clearly a release version number, not a git snapshot or pre-release version.
I remember others not being happy when we were doing workarounds for packages that downstream distros just decided to package out of VCS or snapshots. I don't feel it's right either and I thought you're on that side as well. Anyway, if it really was released, I am OK with this going in.
Regardless of whether its a release or pre-release, this is a clear bug in the code that needs fixing - its just not a workaround for a compiler. As such I've pushed this series. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
On Thu, Feb 23, 2017 at 10:46:14AM +0000, Daniel P. Berrange wrote:
On Thu, Feb 23, 2017 at 11:38:40AM +0100, Martin Kletzander wrote:
On Thu, Feb 23, 2017 at 09:48:48AM +0000, Daniel P. Berrange wrote:
On Wed, Feb 22, 2017 at 09:19:15PM +0100, Martin Kletzander wrote:
On Wed, Feb 22, 2017 at 02:44:01PM -0500, Laine Stump wrote:
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath.
Actually that's not true. Every codepath of the preceding case ends with a "return blah". This is true for the entire function - every case of every switch in the function ends with "return blah". The entire purpose of the function is to determine the flags value, and there are no resources that need cleaning up before returning, so as soon as the value is determined, it immediately returns.
I suppose it could be rewritten to change all of those into "ret = blah; break;", then "return ret;" at the end, but it seemed safer to return immediately than to trust that no new code would be added later in the function (and also it's more compact)
I wonder if this is just a more extreme case of the logic in whatever check necessitated that I add an extra "return 0" at the very end of the function. (that happens even in gcc 6.x; at an earlier point when the function was simpler, that wasn't needed, but after some additions it started producing the "control reaches end of function that requires a return value" or whatever that warning is, and the only way to eliminate it was with the extra return 0.)
If adding the break shuts up the warning, then I guess ACK, but it would probably be better if 1) gcc fixed their incorrect warning, or 2) we switched the entire function to use the less-compact "ret = blah; break;" style instead of returning directly, so there wasn't a single stray break sitting in the middle.
I would say NACK since 1) is the correct option (at least for now), there is no reason for adding more lines of code that don't make sense just because of a compiler version that was not released yet, or does not even have a release plan yet.
GCC 7 *is* released - and has even had a bug fix release too, so ignoring this is not an option. In any case, as Eric mentions this is a genuine bug in our code since we can fall out of the inner switch if the input variable contains a value that doesn't map to an named enum value.
Where did you get the package/tarball? I don't see anything in the release page [1]. On the other hand, when I checked it yesterday, I looked and the development timeline [2] and I thought it's 2016 apparently because when I see the dates now it makes sense that the release should be around the corner. Anyway, even if they did not update the release page, on snapshot ftp [3] there is not even a release candidate.
I didn't use any tarball - just what's in Fedora which is gcc-7.0.1-0.9.fc26.x86_64
Fedora dist-git says the tarball is gcc-7.0.1-20170219.tar.bz2
Odd that its not on the download page though as that's a clearly a release version number, not a git snapshot or pre-release version.
The timestamp indicates it's just a snapshot. GCC doesn't do x.0 releases since gcc-5, I believe, so unless it's 7.1 it's not an official release.
I remember others not being happy when we were doing workarounds for packages that downstream distros just decided to package out of VCS or snapshots. I don't feel it's right either and I thought you're on that side as well. Anyway, if it really was released, I am OK with this going in.
Regardless of whether its a release or pre-release, this is a clear bug in the code that needs fixing - its just not a workaround for a compiler. As such I've pushed this series.
As Laine said as well, there is no bug in the code. All the codepaths in that switch case end with return. And it *is* clearly a bug in the compiler as there are other cases (e.g. VIR_DOMAIN_CONTROLLER_TYPE_SCSI) that behave the same, there is no break after it and the compiler is clearly OK with all the other ones.
Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
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On Thu, Feb 23, 2017 at 01:15:50PM +0100, Martin Kletzander wrote:
On Thu, Feb 23, 2017 at 10:46:14AM +0000, Daniel P. Berrange wrote:
On Thu, Feb 23, 2017 at 11:38:40AM +0100, Martin Kletzander wrote:
On Thu, Feb 23, 2017 at 09:48:48AM +0000, Daniel P. Berrange wrote:
On Wed, Feb 22, 2017 at 09:19:15PM +0100, Martin Kletzander wrote:
On Wed, Feb 22, 2017 at 02:44:01PM -0500, Laine Stump wrote:
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote: > One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags > was missing a break that could result it in falling through to > an incorrect codepath.
Actually that's not true. Every codepath of the preceding case ends with a "return blah". This is true for the entire function - every case of every switch in the function ends with "return blah". The entire purpose of the function is to determine the flags value, and there are no resources that need cleaning up before returning, so as soon as the value is determined, it immediately returns.
I suppose it could be rewritten to change all of those into "ret = blah; break;", then "return ret;" at the end, but it seemed safer to return immediately than to trust that no new code would be added later in the function (and also it's more compact)
I wonder if this is just a more extreme case of the logic in whatever check necessitated that I add an extra "return 0" at the very end of the function. (that happens even in gcc 6.x; at an earlier point when the function was simpler, that wasn't needed, but after some additions it started producing the "control reaches end of function that requires a return value" or whatever that warning is, and the only way to eliminate it was with the extra return 0.)
If adding the break shuts up the warning, then I guess ACK, but it would probably be better if 1) gcc fixed their incorrect warning, or 2) we switched the entire function to use the less-compact "ret = blah; break;" style instead of returning directly, so there wasn't a single stray break sitting in the middle.
I would say NACK since 1) is the correct option (at least for now), there is no reason for adding more lines of code that don't make sense just because of a compiler version that was not released yet, or does not even have a release plan yet.
GCC 7 *is* released - and has even had a bug fix release too, so ignoring this is not an option. In any case, as Eric mentions this is a genuine bug in our code since we can fall out of the inner switch if the input variable contains a value that doesn't map to an named enum value.
Where did you get the package/tarball? I don't see anything in the release page [1]. On the other hand, when I checked it yesterday, I looked and the development timeline [2] and I thought it's 2016 apparently because when I see the dates now it makes sense that the release should be around the corner. Anyway, even if they did not update the release page, on snapshot ftp [3] there is not even a release candidate.
I didn't use any tarball - just what's in Fedora which is gcc-7.0.1-0.9.fc26.x86_64
Fedora dist-git says the tarball is gcc-7.0.1-20170219.tar.bz2
Odd that its not on the download page though as that's a clearly a release version number, not a git snapshot or pre-release version.
The timestamp indicates it's just a snapshot. GCC doesn't do x.0 releases since gcc-5, I believe, so unless it's 7.1 it's not an official release.
I remember others not being happy when we were doing workarounds for packages that downstream distros just decided to package out of VCS or snapshots. I don't feel it's right either and I thought you're on that side as well. Anyway, if it really was released, I am OK with this going in.
Regardless of whether its a release or pre-release, this is a clear bug in the code that needs fixing - its just not a workaround for a compiler. As such I've pushed this series.
As Laine said as well, there is no bug in the code. All the codepaths in that switch case end with return.
No they don't. Nothing in C guarantees that dev->type only contains values that are declared in the enum, particularly since in the struct it is actually an int. We are pretty careful to only store valid values but there's no guarantee we did it correctly, so compiler is right to warn about this. As an example, the following is entirely valid from the C POV dev->type = 10000000; switch ((virDomainDeviceType) dev->type) { and clearly 10000000 is not handled by any switch case. This is no different to us screwing up elsewhere in our code and accidentally setting an invalid enum value.
And it *is* clearly a bug in the compiler as there are other cases (e.g. VIR_DOMAIN_CONTROLLER_TYPE_SCSI) that behave the same, there is no break after it and the compiler is clearly OK with all the other ones.
The bug is in the warning it does *not* produce - it should be warning for that other case too because it suffers the same bug. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
On 02/22/2017 01:44 PM, Laine Stump wrote:
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath.
Actually that's not true. Every codepath of the preceding case ends with a "return blah".
Every explicit codepath. But there are implicit codepaths - the default case. Such paths are unreachable, unless dev->type can ever hold a value that doesn't map to virDomainDeviceType (since we are relying the the compiler to fail compilation if we expand the enum but forget to expand the switch, by intentionally omitting our default case).
This is true for the entire function - every case of every switch in the function ends with "return blah". The entire purpose of the function is to determine the flags value, and there are no resources that need cleaning up before returning, so as soon as the value is determined, it immediately returns.
Gcc is correct - we can fall through to the outer case VIR_DOMAIN_DEVICE_FS: label from the outer case VIR_DOMAIN_DEVICE_CONTROLLER: label, if the inner switch ((virDomainControllerType) cont->type) lands on the (implicit) default: branch because of storing a non-enum value. Such a fallthrough is never going to happen in real life, but adding the break shuts up the compiler, for the same reason that the function ends with: /* We can never get here, because all cases are covered in the * switch, and they all return, but the compiler will still * complain "control reaches end of non-void function" unless * we add the following return. */ return 0; If we weren't opposed to abort() in library code, we could change both the 'break;' and the 'return 0;' into 'abort();', to make it obvious that yes, we really do believe that the implicit default case will never be taken.
I suppose it could be rewritten to change all of those into "ret = blah; break;", then "return ret;" at the end, but it seemed safer to return immediately than to trust that no new code would be added later in the function (and also it's more compact)
I wonder if this is just a more extreme case of the logic in whatever check necessitated that I add an extra "return 0" at the very end of the function. (that happens even in gcc 6.x; at an earlier point when the function was simpler, that wasn't needed, but after some additions it started producing the "control reaches end of function that requires a return value" or whatever that warning is, and the only way to eliminate it was with the extra return 0.)
Yes, it's the same issue.
If adding the break shuts up the warning, then I guess ACK, but it would probably be better if 1) gcc fixed their incorrect warning, or 2) we switched the entire function to use the less-compact "ret = blah; break;" style instead of returning directly, so there wasn't a single stray break sitting in the middle.
I don't think the warning is incorrect. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
On Wed, Feb 22, 2017 at 03:00:41PM -0600, Eric Blake wrote:
On 02/22/2017 01:44 PM, Laine Stump wrote:
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath.
Actually that's not true. Every codepath of the preceding case ends with a "return blah".
Every explicit codepath. But there are implicit codepaths - the default case. Such paths are unreachable, unless dev->type can ever hold a value that doesn't map to virDomainDeviceType (since we are relying the the compiler to fail compilation if we expand the enum but forget to expand the switch, by intentionally omitting our default case).
Yep and such a scenario can happen, because the compiler can't bounds check the value when you have code that casts from an int to the enum, which is exactly what we do when parsing XML.
This is true for the entire function - every case of every switch in the function ends with "return blah". The entire purpose of the function is to determine the flags value, and there are no resources that need cleaning up before returning, so as soon as the value is determined, it immediately returns.
Gcc is correct - we can fall through to the outer case VIR_DOMAIN_DEVICE_FS: label from the outer case VIR_DOMAIN_DEVICE_CONTROLLER: label, if the inner switch ((virDomainControllerType) cont->type) lands on the (implicit) default: branch because of storing a non-enum value.
Such a fallthrough is never going to happen in real life, but adding the break shuts up the compiler, for the same reason that the function ends with:
I could happen in real-life if we have a bug in the code which populates the dev type value since nothing bounds checks the values assigned at runtime.
If adding the break shuts up the warning, then I guess ACK, but it would probably be better if 1) gcc fixed their incorrect warning, or 2) we switched the entire function to use the less-compact "ret = blah; break;" style instead of returning directly, so there wasn't a single stray break sitting in the middle.
I don't think the warning is incorrect.
Indeed, and if the nested switch had a default: case which returnd a value, then the warning would not be triggered. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
On 02/22/2017 11:52 AM, Daniel P. Berrange wrote:
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/qemu/qemu_domain_address.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/src/qemu/qemu_domain_address.c b/src/qemu/qemu_domain_address.c index 5b75044..27ca010 100644 --- a/src/qemu/qemu_domain_address.c +++ b/src/qemu/qemu_domain_address.c @@ -553,6 +553,7 @@ qemuDomainDeviceCalculatePCIConnectFlags(virDomainDeviceDefPtr dev, return pciFlags; } } + break;
Indentation looks weird. I guess its because we have an extra {} scope for allowing declaration of variables? Would hoisting the declaration (not initialization) of case VIR_DOMAIN_DEVICE_CONTROLLER: { virDomainControllerDefPtr cont = dev->data.controller; allow us to get rid of the weird {}? -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
On Wed, Feb 22, 2017 at 02:52:08PM -0600, Eric Blake wrote:
On 02/22/2017 11:52 AM, Daniel P. Berrange wrote:
One of the conditions in qemuDomainDeviceCalculatePCIConnectFlags was missing a break that could result it in falling through to an incorrect codepath.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/qemu/qemu_domain_address.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/src/qemu/qemu_domain_address.c b/src/qemu/qemu_domain_address.c index 5b75044..27ca010 100644 --- a/src/qemu/qemu_domain_address.c +++ b/src/qemu/qemu_domain_address.c @@ -553,6 +553,7 @@ qemuDomainDeviceCalculatePCIConnectFlags(virDomainDeviceDefPtr dev, return pciFlags; } } + break;
Indentation looks weird. I guess its because we have an extra {} scope for allowing declaration of variables? Would hoisting the declaration (not initialization) of
case VIR_DOMAIN_DEVICE_CONTROLLER: { virDomainControllerDefPtr cont = dev->data.controller;
allow us to get rid of the weird {}?
Yes, though this style is not that unusual - we've got it in a number of other places in libvirt already where we want to isolate the variable declaration, so I think this is ok as is. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
In GCC 7 there is a new warning triggered when a switch case has a conditional statement (eg if ... else...) and some of the code paths fallthrough to the next switch statement. e.g. conf/domain_conf.c: In function 'virDomainChrEquals': conf/domain_conf.c:14926:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (src->targetTypeAttr != tgt->targetTypeAttr) ^ conf/domain_conf.c:14928:5: note: here case VIR_DOMAIN_CHR_DEVICE_TYPE_CONSOLE: ^~~~ conf/domain_conf.c: In function 'virDomainChrDefFormat': conf/domain_conf.c:22143:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (def->targetTypeAttr) { ^ conf/domain_conf.c:22151:5: note: here default: ^~~~~~~ GCC introduced a __attribute__((fallthrough)) to let you indicate that this is intentionale behaviour rather than a bug. Signed-off-by: Daniel P. Berrange <berrange@redhat.com> --- src/conf/domain_conf.c | 7 +++++++ src/conf/network_conf.c | 3 ++- src/internal.h | 8 ++++++++ src/lxc/lxc_container.c | 2 +- src/network/bridge_driver.c | 6 ++++++ tools/virsh-edit.c | 2 +- 6 files changed, 25 insertions(+), 3 deletions(-) diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c index f718b9a..17995f7 100644 --- a/src/conf/domain_conf.c +++ b/src/conf/domain_conf.c @@ -14925,7 +14925,12 @@ virDomainChrEquals(virDomainChrDefPtr src, case VIR_DOMAIN_CHR_DEVICE_TYPE_SERIAL: if (src->targetTypeAttr != tgt->targetTypeAttr) return false; + + ATTRIBUTE_FALLTHROUGH; + case VIR_DOMAIN_CHR_DEVICE_TYPE_CONSOLE: + ATTRIBUTE_FALLTHROUGH; + case VIR_DOMAIN_CHR_DEVICE_TYPE_PARALLEL: return src->target.port == tgt->target.port; break; @@ -22148,6 +22153,8 @@ virDomainChrDefFormat(virBufferPtr buf, def->target.port); break; } + ATTRIBUTE_FALLTHROUGH; + default: virBufferAsprintf(buf, "<target port='%d'/>\n", def->target.port); diff --git a/src/conf/network_conf.c b/src/conf/network_conf.c index 0e20dac..48e0001 100644 --- a/src/conf/network_conf.c +++ b/src/conf/network_conf.c @@ -2442,7 +2442,8 @@ virNetworkDefParseXML(xmlXPathContextPtr ctxt) def->name); goto error; } - /* fall through to next case */ + ATTRIBUTE_FALLTHROUGH; + case VIR_NETWORK_FORWARD_BRIDGE: if (def->delay || stp) { virReportError(VIR_ERR_XML_ERROR, diff --git a/src/internal.h b/src/internal.h index 334659d..74a43fa 100644 --- a/src/internal.h +++ b/src/internal.h @@ -218,6 +218,10 @@ # endif # endif +# ifndef ATTRIBUTE_FALLTHROUGH +# define ATTRIBUTE_FALLTHROUGH __attribute__((fallthrough)) +# endif + # else # ifndef ATTRIBUTE_UNUSED # define ATTRIBUTE_UNUSED @@ -228,6 +232,10 @@ # ifndef ATTRIBUTE_RETURN_CHECK # define ATTRIBUTE_RETURN_CHECK # endif +# +# ifndef ATTRIBUTE_FALLTHROUGH +# define ATTRIBUTE_FALLTHROUGH do {} while(0) +# endif # endif /* __GNUC__ */ diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c index 601b9b0..99bd7e9 100644 --- a/src/lxc/lxc_container.c +++ b/src/lxc/lxc_container.c @@ -2042,7 +2042,7 @@ static int lxcContainerDropCapabilities(virDomainDefPtr def, default: /* User specified capabilities to drop */ toDrop = (state == VIR_TRISTATE_SWITCH_OFF); } - /* Fallthrough */ + ATTRIBUTE_FALLTHROUGH; case VIR_DOMAIN_CAPABILITIES_POLICY_ALLOW: if (policy == VIR_DOMAIN_CAPABILITIES_POLICY_ALLOW) diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c index 06759c6..c5ec282 100644 --- a/src/network/bridge_driver.c +++ b/src/network/bridge_driver.c @@ -2715,6 +2715,8 @@ networkStartNetwork(virNetworkDriverStatePtr driver, * VIR_NETWORK_FORWARD_BRIDGE with no bridge device defined * (since that is macvtap bridge mode). */ + ATTRIBUTE_FALLTHROUGH; + case VIR_NETWORK_FORWARD_PRIVATE: case VIR_NETWORK_FORWARD_VEPA: case VIR_NETWORK_FORWARD_PASSTHROUGH: @@ -2792,6 +2794,8 @@ networkShutdownNetwork(virNetworkDriverStatePtr driver, * VIR_NETWORK_FORWARD_BRIDGE with no bridge device defined * (since that is macvtap bridge mode). */ + ATTRIBUTE_FALLTHROUGH; + case VIR_NETWORK_FORWARD_PRIVATE: case VIR_NETWORK_FORWARD_VEPA: case VIR_NETWORK_FORWARD_PASSTHROUGH: @@ -4974,6 +4978,8 @@ networkGetNetworkAddress(const char *netname, char **netaddr) * fall through if netdef->bridge wasn't set, since that is * macvtap bridge mode network. */ + ATTRIBUTE_FALLTHROUGH; + case VIR_NETWORK_FORWARD_PRIVATE: case VIR_NETWORK_FORWARD_VEPA: case VIR_NETWORK_FORWARD_PASSTHROUGH: diff --git a/tools/virsh-edit.c b/tools/virsh-edit.c index 16d6705..92a00b7 100644 --- a/tools/virsh-edit.c +++ b/tools/virsh-edit.c @@ -140,7 +140,7 @@ do { goto redefine; break; } - /* fall-through */ + ATTRIBUTE_FALLTHROUGH; #endif default: -- 2.9.3
On Wed, Feb 22, 2017 at 05:52:05PM +0000, Daniel P. Berrange wrote:
In GCC 7 there is a new warning triggered when a switch case has a conditional statement (eg if ... else...) and some of the code paths fallthrough to the next switch statement. e.g.
conf/domain_conf.c: In function 'virDomainChrEquals': conf/domain_conf.c:14926:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (src->targetTypeAttr != tgt->targetTypeAttr) ^ conf/domain_conf.c:14928:5: note: here case VIR_DOMAIN_CHR_DEVICE_TYPE_CONSOLE: ^~~~ conf/domain_conf.c: In function 'virDomainChrDefFormat': conf/domain_conf.c:22143:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (def->targetTypeAttr) { ^ conf/domain_conf.c:22151:5: note: here default: ^~~~~~~
GCC introduced a __attribute__((fallthrough)) to let you indicate that this is intentionale behaviour rather than a bug.
BTW, CLang has apparently had an -Wimplicit-fallthrough warning flag for a while, and also seems to have the same __attribute__((fallthrough)), but I've been unable to get CLang to trigger such warnings, and hence did not enable __attribute__((fallthrough)) on CLang. If someone can figure out how to reproduce the warnings on clang we could extend internal.h to surpress them for whichever clang version introduced the warnings. As is, the ATTRIBUTE_FALLTHROUGH turns into a no-op for CLang unless it claims GCC 7.0 compatibility. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
Daniel P. Berrange wrote:
On Wed, Feb 22, 2017 at 05:52:05PM +0000, Daniel P. Berrange wrote:
In GCC 7 there is a new warning triggered when a switch case has a conditional statement (eg if ... else...) and some of the code paths fallthrough to the next switch statement. e.g.
conf/domain_conf.c: In function 'virDomainChrEquals': conf/domain_conf.c:14926:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (src->targetTypeAttr != tgt->targetTypeAttr) ^ conf/domain_conf.c:14928:5: note: here case VIR_DOMAIN_CHR_DEVICE_TYPE_CONSOLE: ^~~~ conf/domain_conf.c: In function 'virDomainChrDefFormat': conf/domain_conf.c:22143:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (def->targetTypeAttr) { ^ conf/domain_conf.c:22151:5: note: here default: ^~~~~~~
GCC introduced a __attribute__((fallthrough)) to let you indicate that this is intentionale behaviour rather than a bug.
BTW, CLang has apparently had an -Wimplicit-fallthrough warning flag for a while, and also seems to have the same __attribute__((fallthrough)), but I've been unable to get CLang to trigger such warnings, and hence did not enable __attribute__((fallthrough)) on CLang. If someone can figure out how to reproduce the warnings on clang we could extend internal.h to surpress them for whichever clang version introduced the warnings. As is, the ATTRIBUTE_FALLTHROUGH turns into a no-op for CLang unless it claims GCC 7.0 compatibility.
It *looks* like -Wimplicit-fallthrough in clang is only effective for C++11: http://clang-developers.42468.n3.nabble.com/should-Wimplicit-fallthrough-req... It mentions this commit: http://llvm.org/viewvc/llvm-project?revision=167655&view=revision And it seems it wasn't changed since than. Roman Bogorodskiy
On Thu, Feb 23, 2017 at 09:07:59PM +0400, Roman Bogorodskiy wrote:
Daniel P. Berrange wrote:
On Wed, Feb 22, 2017 at 05:52:05PM +0000, Daniel P. Berrange wrote:
In GCC 7 there is a new warning triggered when a switch case has a conditional statement (eg if ... else...) and some of the code paths fallthrough to the next switch statement. e.g.
conf/domain_conf.c: In function 'virDomainChrEquals': conf/domain_conf.c:14926:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (src->targetTypeAttr != tgt->targetTypeAttr) ^ conf/domain_conf.c:14928:5: note: here case VIR_DOMAIN_CHR_DEVICE_TYPE_CONSOLE: ^~~~ conf/domain_conf.c: In function 'virDomainChrDefFormat': conf/domain_conf.c:22143:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (def->targetTypeAttr) { ^ conf/domain_conf.c:22151:5: note: here default: ^~~~~~~
GCC introduced a __attribute__((fallthrough)) to let you indicate that this is intentionale behaviour rather than a bug.
BTW, CLang has apparently had an -Wimplicit-fallthrough warning flag for a while, and also seems to have the same __attribute__((fallthrough)), but I've been unable to get CLang to trigger such warnings, and hence did not enable __attribute__((fallthrough)) on CLang. If someone can figure out how to reproduce the warnings on clang we could extend internal.h to surpress them for whichever clang version introduced the warnings. As is, the ATTRIBUTE_FALLTHROUGH turns into a no-op for CLang unless it claims GCC 7.0 compatibility.
It *looks* like -Wimplicit-fallthrough in clang is only effective for C++11:
http://clang-developers.42468.n3.nabble.com/should-Wimplicit-fallthrough-req...
It mentions this commit:
http://llvm.org/viewvc/llvm-project?revision=167655&view=revision
And it seems it wasn't changed since than.
Ah I see. So they disabled it for C, because their [[clang::fallthrough]] magic annotation would not work under C. Hopefully they'll enable it one day with the more normal __attribute__((fallthrough)) syntax for C. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
On 02/22/2017 12:52 PM, Daniel P. Berrange wrote:
In GCC 7 there is a new warning triggered when a switch case has a conditional statement (eg if ... else...) and some of the code paths fallthrough to the next switch statement. e.g.
conf/domain_conf.c: In function 'virDomainChrEquals': conf/domain_conf.c:14926:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (src->targetTypeAttr != tgt->targetTypeAttr) ^ conf/domain_conf.c:14928:5: note: here case VIR_DOMAIN_CHR_DEVICE_TYPE_CONSOLE: ^~~~ conf/domain_conf.c: In function 'virDomainChrDefFormat': conf/domain_conf.c:22143:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (def->targetTypeAttr) { ^ conf/domain_conf.c:22151:5: note: here default: ^~~~~~~
GCC introduced a __attribute__((fallthrough)) to let you indicate that this is intentionale behaviour rather than a bug.
ACK.
On 02/22/2017 11:52 AM, Daniel P. Berrange wrote:
In GCC 7 there is a new warning triggered when a switch case has a conditional statement (eg if ... else...) and some of the code paths fallthrough to the next switch statement. e.g.
conf/domain_conf.c: In function 'virDomainChrEquals': conf/domain_conf.c:14926:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (src->targetTypeAttr != tgt->targetTypeAttr) ^
+++ b/src/conf/domain_conf.c @@ -14925,7 +14925,12 @@ virDomainChrEquals(virDomainChrDefPtr src, case VIR_DOMAIN_CHR_DEVICE_TYPE_SERIAL: if (src->targetTypeAttr != tgt->targetTypeAttr) return false; + + ATTRIBUTE_FALLTHROUGH; +
I understand this one...
case VIR_DOMAIN_CHR_DEVICE_TYPE_CONSOLE: + ATTRIBUTE_FALLTHROUGH; + case VIR_DOMAIN_CHR_DEVICE_TYPE_PARALLEL:
...but was this one necessary, or is gcc smart enough to know that two consecutive labels never needs an explicit fallthrough? Also, is it sufficient to spell it: /* fall through */ so that Coverity can also recognize it? Or does gcc not recognize the magic comment?
+++ b/src/internal.h @@ -218,6 +218,10 @@ # endif # endif
+# ifndef ATTRIBUTE_FALLTHROUGH +# define ATTRIBUTE_FALLTHROUGH __attribute__((fallthrough)) +# endif
If the magic /* fall through */ comment is sufficient, then we don't need this macro.
+++ b/src/lxc/lxc_container.c @@ -2042,7 +2042,7 @@ static int lxcContainerDropCapabilities(virDomainDefPtr def, default: /* User specified capabilities to drop */ toDrop = (state == VIR_TRISTATE_SWITCH_OFF); } - /* Fallthrough */ + ATTRIBUTE_FALLTHROUGH;
Hmm - this argues at least one comment spelling that gcc does not recognize.
+++ b/tools/virsh-edit.c @@ -140,7 +140,7 @@ do { goto redefine; break; } - /* fall-through */ + ATTRIBUTE_FALLTHROUGH; #endif
and another. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
On Wed, Feb 22, 2017 at 02:49:12PM -0600, Eric Blake wrote:
On 02/22/2017 11:52 AM, Daniel P. Berrange wrote:
In GCC 7 there is a new warning triggered when a switch case has a conditional statement (eg if ... else...) and some of the code paths fallthrough to the next switch statement. e.g.
conf/domain_conf.c: In function 'virDomainChrEquals': conf/domain_conf.c:14926:12: error: this statement may fall through [-Werror=implicit-fallthrough=] if (src->targetTypeAttr != tgt->targetTypeAttr) ^
+++ b/src/conf/domain_conf.c @@ -14925,7 +14925,12 @@ virDomainChrEquals(virDomainChrDefPtr src, case VIR_DOMAIN_CHR_DEVICE_TYPE_SERIAL: if (src->targetTypeAttr != tgt->targetTypeAttr) return false; + + ATTRIBUTE_FALLTHROUGH; +
I understand this one...
case VIR_DOMAIN_CHR_DEVICE_TYPE_CONSOLE: + ATTRIBUTE_FALLTHROUGH; + case VIR_DOMAIN_CHR_DEVICE_TYPE_PARALLEL:
...but was this one necessary, or is gcc smart enough to know that two consecutive labels never needs an explicit fallthrough?
Yeah, that second one was bogus - i added it by mistake.
Also, is it sufficient to spell it:
/* fall through */
so that Coverity can also recognize it? Or does gcc not recognize the magic comment?
IIUC, it only likes an all lowercase 'fallthrough' comment, but I'm not inclined to use that. CLang doesn't parse comments at all and relies on the attribute annotation. Given that both GCC & CLang now support the same attribute name for this, I would expect Coverity will learn about it too in the not too distant future. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
participants (7)
-
Andrea Bolognani -
Daniel P. Berrange -
Eric Blake -
Laine Stump -
Martin Kletzander -
Michal Privoznik -
Roman Bogorodskiy