diff options
| author | Peter Maydell <peter.maydell@linaro.org> | 2021-01-29 13:03:30 +0000 |
|---|---|---|
| committer | Peter Maydell <peter.maydell@linaro.org> | 2021-02-11 11:50:14 +0000 |
| commit | e6a41a045c298538d303cd8fe8d7ae29a0c066ad (patch) | |
| tree | 717347b1e60ed8d698fb414d81eff809c0b06967 | |
| parent | 932a8d1f11ccfbf196ee6fb4a5ccdf274b14a78c (diff) | |
accel/tcg: Add URL of clang bug to comment about our workaround
In cpu_exec() we have a longstanding workaround for compilers which
do not correctly implement the part of the sigsetjmp()/siglongjmp()
spec which requires that local variables which are not changed
between the setjmp and the longjmp retain their value.
I recently ran across the upstream clang bug report for this; add a
link to it to the comment describing the workaround, and generally
expand the comment, so that we have a reasonable chance in future of
understanding why it's there and determining when we can remove it,
assuming clang eventually fixes the bug.
Remove the /* buggy compiler */ comments on the #else and #endif:
they don't add anything to understanding and are somewhat misleading
since they're sandwiching the code path for *non*-buggy compilers.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20210129130330.30820-1-peter.maydell@linaro.org
| -rw-r--r-- | accel/tcg/cpu-exec.c | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c index d9ef69121c..f2819eec7d 100644 --- a/accel/tcg/cpu-exec.c +++ b/accel/tcg/cpu-exec.c @@ -773,17 +773,30 @@ int cpu_exec(CPUState *cpu) /* prepare setjmp context for exception handling */ if (sigsetjmp(cpu->jmp_env, 0) != 0) { #if defined(__clang__) - /* Some compilers wrongly smash all local variables after - * siglongjmp. There were bug reports for gcc 4.5.0 and clang. + /* + * Some compilers wrongly smash all local variables after + * siglongjmp (the spec requires that only non-volatile locals + * which are changed between the sigsetjmp and siglongjmp are + * permitted to be trashed). There were bug reports for gcc + * 4.5.0 and clang. The bug is fixed in all versions of gcc + * that we support, but is still unfixed in clang: + * https://bugs.llvm.org/show_bug.cgi?id=21183 + * * Reload essential local variables here for those compilers. - * Newer versions of gcc would complain about this code (-Wclobbered). */ + * Newer versions of gcc would complain about this code (-Wclobbered), + * so we only perform the workaround for clang. + */ cpu = current_cpu; cc = CPU_GET_CLASS(cpu); -#else /* buggy compiler */ - /* Assert that the compiler does not smash local variables. */ +#else + /* + * Non-buggy compilers preserve these locals; assert that + * they have the correct value. + */ g_assert(cpu == current_cpu); g_assert(cc == CPU_GET_CLASS(cpu)); -#endif /* buggy compiler */ +#endif + #ifndef CONFIG_SOFTMMU tcg_debug_assert(!have_mmap_lock()); #endif |