Re: [libvirt] [PATCH] Fix qemuMigrationToFile nonull annotation
On 05/05/2011 04:38 AM, Daniel P. Berrange wrote:
The qemuMigrationToFile method was accidentally annotated for
the 'compressor' parameter to be non-null, instead of the
'path' parameter. Thus GCC with -O2, unhelpfully deleted the
entire 'if (compressor == NULL)' block of code during
optimization. Thus NULL was passed to virCommandNew() with
predictably bad results.
Regression introduced in commit 7c31e1e, so fortunately 0.9.1 is immune.
This shows that the 'ATTRIBUTE_NONNULL' annotation is
actually
really very dangerous to use. GCC is incapable of issuing any
warnings about callers passing NULL, unless they pass a literal
"NULL". If the caller does 'void *p = NULL; foo(p)' it will not
warn. GCC is also not warning about the fact that there is a
huge block of code for 'if (compressor == NULL)' that is "dead"
code and being deleted.
While it is perhaps nice to have ATTRIBUTE_NONNULL for static
analysis tools like clang, IMHO, it is too dangerous for us
to continue to have it enabled in builds. I think we should
define it to a no-op macro, unless explicitly enabled with
configure.
Hmm, maybe you're right, although it should still be defined for cases
when compiling with a static analyzer (such as how sa_assert is a no-op
for gcc but does something important for clang).
Maybe we should also file an enhancement request against gcc, to alter
the syntax for attribute-nonnull. That is,
void f(void *a, void *b) ATTRIBUTE_NONNULL(2,b)
would be nicer, where gcc complains if parameter 2 is not named b, so
that the mere deletion of parameter a catches this sort of mistake faster.
+++ b/src/qemu/qemu_migration.h
@@ -64,7 +64,7 @@ int qemuMigrationToFile(struct qemud_driver *driver, virDomainObjPtr
vm,
int fd, off_t offset, const char *path,
const char *compressor,
bool is_reg, bool bypassSecurityDriver)
- ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(6)
+ ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(5)
ATTRIBUTE_RETURN_CHECK;
ACK.
--
Eric Blake eblake(a)redhat.com +1-801-349-2682
Libvirt virtualization library http://libvirt.org
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