On Tue, 2024-10-22 at 13:36 -0700, Pierrick Bouvier wrote:
On 10/22/24 03:56, Alex Bennée wrote:
From: Ilya Leoshkevich <iii@linux.ibm.com>
commit f025692c992c ("accel/tcg: Clear PAGE_WRITE before translation") fixed cross-modifying code handling, but did not add a test. The changed code was further improved recently [1], and I was not sure whether these modifications were safe (spoiler: they were fine).
Add a test to make sure there are no regressions.
[1] https://lists.gnu.org/archive/html/qemu-devel/2022-09/msg00034.html
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Message-Id: <20241001150617.9977-1-iii@linux.ibm.com> Signed-off-by: Alex Bennée <alex.bennee@linaro.org> --- tests/tcg/x86_64/cross-modifying-code.c | 80 +++++++++++++++++++++++++ tests/tcg/x86_64/Makefile.target | 4 ++ 2 files changed, 84 insertions(+) create mode 100644 tests/tcg/x86_64/cross-modifying-code.c
diff --git a/tests/tcg/x86_64/cross-modifying-code.c b/tests/tcg/x86_64/cross-modifying-code.c new file mode 100644 index 0000000000..2704df6061 --- /dev/null +++ b/tests/tcg/x86_64/cross-modifying-code.c @@ -0,0 +1,80 @@ +/* + * Test patching code, running in one thread, from another thread. + * + * Intel SDM calls this "cross-modifying code" and recommends a special + * sequence, which requires both threads to cooperate. + * + * Linux kernel uses a different sequence that does not require cooperation and + * involves patching the first byte with int3. + * + * Finally, there is user-mode software out there that simply uses atomics, and + * that seems to be good enough in practice. Test that QEMU has no problems + * with this as well. + */ + +#include <assert.h> +#include <pthread.h> +#include <stdbool.h> +#include <stdlib.h> + +void add1_or_nop(long *x); +asm(".pushsection .rwx,\"awx\",@progbits\n" + ".globl add1_or_nop\n" + /* addq $0x1,(%rdi) */ + "add1_or_nop: .byte 0x48, 0x83, 0x07, 0x01\n" + "ret\n" + ".popsection\n"); + +#define THREAD_WAIT 0 +#define THREAD_PATCH 1 +#define THREAD_STOP 2 + +static void *thread_func(void *arg) +{ + int val = 0x0026748d; /* nop */ + + while (true) { + switch (__atomic_load_n((int *)arg, __ATOMIC_SEQ_CST)) { + case THREAD_WAIT: + break; + case THREAD_PATCH: + val = __atomic_exchange_n((int *)&add1_or_nop, val, + __ATOMIC_SEQ_CST); + break; + case THREAD_STOP: + return NULL; + default: + assert(false); + __builtin_unreachable();
Use g_assert_not_reached() instead. checkpatch emits an error for it now.
Is there an easy way to include glib from testcases? It's located using meson, and I can't immediately see how to push the respective compiler flags to the test Makefiles - this seems to be currently handled by configure writing to $config_target_mak. [...]