Recent ntdll/unix/signal_x86_64.c changes

[Gerald Pfeifer]

commit ea640f6cece7660ffc853b7d574fbe52af34901a
Author: Alexandre Julliard 
Date:   Mon Sep 11 11:25:29 2023 +0200

ntdll: Ignore attempts to change segment registers on x86-64.

moved the following code

+#ifdef DS_sig
  +    DS_sig(sigcontext) = ds64_sel;
  +#else
  +    __asm__ volatile( "movw %0,%%ds" :: "r" (ds64_sel) );
  +#endif
  +#ifdef ES_sig
  +    ES_sig(sigcontext) = ds64_sel;
  +#else
  +    __asm__ volatile( "movw %0,%%es" :: "r" (ds64_sel) );
  +#endif

into

static inline void leave_handler( const ucontext_t *sigcontext )

Alas this has "const ucontext_t *sigcontext", so platforms like
FreeBSD that define DS_sig will try to do

DS_sig(sigcontext) = ds64_sel;

which results in GCC rightfully diagnosing:

dlls/ntdll/unix/signal_x86_64.c: In function ‘leave_handler’:
  dlls/ntdll/unix/signal_x86_64.c:822:24: error: assignment of member ‘mc_ds’ in read-only object
    822 |     DS_sig(sigcontext) = ds64_sel;
        |                        ^

I submitted https://gitlab.winehq.org/wine/wine/-/merge_requests/3845 
which restores the build on FreeBSD and presumably NetBSD, but wonder:

Could FreeBSD/NetBSD align with Linux and macOS which d not define DS_sig 
(and ES_sig) and thus use into different code paths in leave_handler?

Gerald

[Alexandre Julliard]

Gerald Pfeifer  writes:
> I submitted https://gitlab.winehq.org/wine/wine/-/merge_requests/3845 
> which restores the build on FreeBSD and presumably NetBSD, but wonder:
>
> Could FreeBSD/NetBSD align with Linux and macOS which d not define DS_sig 
> (and ES_sig) and thus use into different code paths in leave_handler?

It depends on whether the kernel restores them from the context on
signal return. My guess is that it does since they are defined in
ucontext_t.

We have tests for this in dlls/ntdll/tests/exception.c, so you can try
both approaches and see which one breaks the tests.