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

[Philippe Mathieu-Daudé]

Hi Pierrick,

On 13/2/23 17:13, 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 | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h
> index 5b38c7bd04..84f62d0a17 100644
> --- a/include/sysemu/os-win32.h
> +++ b/include/sysemu/os-win32.h
> @@ -51,14 +51,28 @@ typedef struct sockaddr_un {
>   extern "C" {
>   #endif
>   
> -#if defined(_WIN64)
> +#if defined(__aarch64__)

Shouldn't we check for __MINGW64__?

   #if defined(__aarch64__) && defined(__MINGW64__)

> +/* 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. */

So this is not stable. Better would be to check the symbols availability
at link-time via meson; see for example glusterfs_ftruncate_has_stat
which defines CONFIG_GLUSTERFS_FTRUNCATE_HAS_STAT.

A similar check could define CONFIG_MINGW64_HAS_SETJMP_LONGJMP.

> +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

Regards,

Phil.