Re: [PATCH v3 2/4] sysemu/os-win32: fix setjmp/longjmp on windows-arm64

[Pierrick Bouvier]

@Philippe Mathieu-Daudé, is that version satisfying for you, regarding 
your initial comments about setjmp/longjmp detection in meson?

I can integrate more changes if needed.

Thanks,
Pierrick

On 2/20/23 16:16, Pierrick Bouvier wrote:
> Acked-by: Richard Henderson <richard.henderson@linaro.org>
>
> On 2/20/23 12:12, Pierrick Bouvier wrote:
> > Windows implementation of setjmp/longjmp is done in
> > C:/WINDOWS/system32/ucrtbase.dll. Alas, on arm64, it seems to *always*
> > perform stack unwinding, which crashes from generated code.
> >
> > By using alternative implementation built in mingw, we avoid doing stack
> > unwinding and this fixes crash when calling longjmp.
> >
> > Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> > ---
> >    include/sysemu/os-win32.h | 25 +++++++++++++++++++++++--
> >    meson.build               | 24 ++++++++++++++++++++++++
> >    2 files changed, 47 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h
> > index 5b38c7bd04..1f6c141d39 100644
> > --- a/include/sysemu/os-win32.h
> > +++ b/include/sysemu/os-win32.h
> > @@ -51,14 +51,35 @@ typedef struct sockaddr_un {
> >    extern "C" {
> >    #endif
> >    
> > -#if defined(_WIN64)
> > +#if defined(__aarch64__)
> > +#ifndef CONFIG_MINGW64_HAS_SETJMP_LONGJMP
> > +#error mingw must provide setjmp/longjmp for windows-arm64
> > +#endif
> > +/*
> > + * On windows-arm64, setjmp is available in only one variant, and longjmp 
> > always
> > + * does stack unwinding. This crash with generated code.
> > + * Thus, we use another implementation of setjmp (not windows one), coming from
> > + * mingw, which never performs stack unwinding.
> > + */
> > +#undef setjmp
> > +#undef longjmp
> > +/*
> > + * These functions are not declared in setjmp.h because __aarch64__ defines
> > + * setjmp to _setjmpex instead. However, they are still defined in 
> > libmingwex.a,
> > + * which gets linked automatically.
> > + */
> > +extern int __mingw_setjmp(jmp_buf);
> > +extern void __attribute__((noreturn)) __mingw_longjmp(jmp_buf, int);
> > +#define setjmp(env) __mingw_setjmp(env)
> > +#define longjmp(env, val) __mingw_longjmp(env, val)
> > +#elif defined(_WIN64)
> >    /* On w64, setjmp is implemented by _setjmp which needs a second parameter.
> >     * If this parameter is NULL, longjump does no stack unwinding.
> >     * That is what we need for QEMU. Passing the value of register rsp (default)
> >     * lets longjmp try a stack unwinding which will crash with generated code. 
> > */
> >    # undef setjmp
> >    # define setjmp(env) _setjmp(env, NULL)
> > -#endif
> > +#endif /* __aarch64__ */
> >    /* QEMU uses sigsetjmp()/siglongjmp() as the portable way to specify
> >     * "longjmp and don't touch the signal masks". Since we know that the
> >     * savemask parameter will always be zero we can safely define these
> > diff --git a/meson.build b/meson.build
> > index 4ba3bf3431..e968ed9e7a 100644
> > --- a/meson.build
> > +++ b/meson.build
> > @@ -2450,6 +2450,30 @@ if targetos == 'windows'
> >        }''', name: '_lock_file and _unlock_file'))
> >    endif
> >    
> > +if targetos == 'windows'
> > +  mingw_has_setjmp_longjmp = cc.links('''
> > +    #include <setjmp.h>
> > +    int main(void) {
> > +      /*
> > +       * These functions are not available in setjmp header, but may be
> > +       * available at link time, from libmingwex.a.
> > +       */
> > +      extern int __mingw_setjmp(jmp_buf);
> > +      extern void __attribute__((noreturn)) __mingw_longjmp(jmp_buf, int);
> > +      jmp_buf env;
> > +      __mingw_setjmp(env);
> > +      __mingw_longjmp(env, 0);
> > +    }
> > +  ''', name: 'mingw setjmp and longjmp')
> > +
> > +  config_host_data.set('CONFIG_MINGW64_HAS_SETJMP_LONGJMP',
> > +                       mingw_has_setjmp_longjmp)
> > +
> > +  if cpu == 'aarch64' and not mingw_has_setjmp_longjmp
> > +    error('mingw must provide setjmp/longjmp for windows-arm64')
> > +  endif
> > +endif
> > +
> >    ########################
> >    # Target configuration #
> >    ########################