On 27/10/2015 19:31, Stefan Weil wrote: > Am 26.09.2015 um 13:23 schrieb Stefan Weil: >> Reloading of local variables after sigsetjmp is only needed for some >> buggy compilers. >> >> The code which should reload these variables causes compiler warnings >> with gcc 4.7 when compiler optimizations are enabled: >> >> cpu-exec.c:204:15: error: >> variable ‘cpu’ might be clobbered by ‘longjmp’ or ‘vfork’ >> [-Werror=clobbered] >> cpu-exec.c:207:15: error: >> variable ‘cc’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered] >> cpu-exec.c:202:28: error: >> argument ‘env’ might be clobbered by ‘longjmp’ or ‘vfork’ >> [-Werror=clobbered] >> >> Now this code is only used for compilers which need it >> (and gcc 4.5.x, x > 0 which does not need it but won't give warnings). >> >> There were bug reports for clang and gcc 4.5.0, while gcc 4.5.1 >> was reported to work fine without the reload code. For clang it >> is not clear which versions are affected, so simply keep the status quo >> for all clang compilations. This can be improved later. >> >> Signed-off-by: Stefan Weil <s...@weilnetz.de> >> --- >> >> v2: Don't remove the code which causes the warnings, but use it >> only with clang or gcc < 4.6. >> >> v3: Add assertions for compilers which hopefully don't smash variables >> (suggested by Peter Maydell). >> >> I started v1 of this patch two years ago to prepare support for >> builds with compiler option -Wextra. >> >> See http://patchwork.ozlabs.org/patch/287593/ for the latest >> discussion on this issue. >> >> >> cpu-exec.c | 18 +++++++++++++++--- >> 1 file changed, 15 insertions(+), 3 deletions(-) >> >> diff --git a/cpu-exec.c b/cpu-exec.c >> index 8fd56a6..7dab85a 100644 >> --- a/cpu-exec.c >> +++ b/cpu-exec.c >> @@ -538,15 +538,27 @@ int cpu_exec(CPUState *cpu) >> only be set by a memory fault) */ >> } /* for(;;) */ >> } else { >> - /* Reload env after longjmp - the compiler may have smashed all >> - * local variables as longjmp is marked 'noreturn'. */ >> +#if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6) >> + /* Some compilers wrongly smash all local variables after >> + * siglongjmp. There were bug reports for gcc 4.5.0 and clang. >> + * Reload essential local variables here for those compilers. >> + * Newer versions of gcc would complain about this code >> (-Wclobbered). */ >> cpu = current_cpu; >> cc = CPU_GET_CLASS(cpu); >> - cpu->can_do_io = 1; >> #ifdef TARGET_I386 >> x86_cpu = X86_CPU(cpu); >> env = &x86_cpu->env; >> #endif >> +#else /* buggy compiler */ >> + /* Assert that the compiler does not smash local variables. */ >> + g_assert(cpu == current_cpu); >> + g_assert(cc == CPU_GET_CLASS(cpu)); >> +#ifdef TARGET_I386 >> + g_assert(x86_cpu == X86_CPU(cpu)); >> + g_assert(env == &x86_cpu->env); >> +#endif >> +#endif /* buggy compiler */ >> + cpu->can_do_io = 1; >> tb_lock_reset(); >> } >> } /* for(;;) */ >> > > > Ping. Is there any chance to get this patch into version 2.5? > I'd be happy to remove this 2 year old issue from my list of > open patches.
Yes, I'll send a pull request next week. Paolo
