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. Regards, Stefan
