Re: [RFC PATCH 7/9] hurd: Generalize init-first.c to support x86_64

[Noah Goldstein <goldstein.w.n@gmail.com>]

On Sat, Feb 18, 2023 at 2:40 PM Sergey Bugaev via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
> ---
>  sysdeps/mach/hurd/{i386 => x86}/init-first.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
>  rename sysdeps/mach/hurd/{i386 => x86}/init-first.c (96%)
>
> diff --git a/sysdeps/mach/hurd/i386/init-first.c b/sysdeps/mach/hurd/x86/init-first.c
> similarity index 96%
> rename from sysdeps/mach/hurd/i386/init-first.c
> rename to sysdeps/mach/hurd/x86/init-first.c
> index a558da16..75ac1ff2 100644
> --- a/sysdeps/mach/hurd/i386/init-first.c
> +++ b/sysdeps/mach/hurd/x86/init-first.c
> @@ -227,10 +227,15 @@ init (int *data)
>     values we set just above.  We have stashed in %eax the user code
>     return address.  Push it on the top of the stack so it acts as
>     init1's return address, and then jump there.  */
> +#ifdef __x86_64__
> +asm ("call_init1:\n"
> +     "  push %rax\n"
> +     "  jmp *%rcx\n");
> +#else
>  asm ("call_init1:\n"
>       " push %eax\n"
>       " jmp *%ecx\n");
> -
> +#endif
>
>  /* Do the first essential initializations that must precede all else.  */
>  static inline void
> @@ -242,7 +247,7 @@ first_init (void)
>  #ifndef SHARED
>    /* In the static case, we need to set up TLS early so that the stack
>       protection guard can be read at gs:0x14 by the gcc-generated snippets.  */
> -  _hurd_tls_init(&__init1_tcbhead);
> +  _hurd_tls_init (&__init1_tcbhead);
>    asm ("movw %%gs,%w0" : "=m" (__init1_desc));
>  #endif
>
> @@ -300,7 +305,7 @@ _hurd_stack_setup (void)
>         {
>           /* If we use ``__builtin_frame_address (0) + 2'' here, GCC gets
>              confused.  */
> -         init ((int *) &argc);
> +         init (&argc);
>         }
>
>        /* Push the user return address after the argument data, and then
> @@ -308,9 +313,15 @@ _hurd_stack_setup (void)
>          caller had called `doinit1' with the argument data already on the
>          stack.  */
>        *--data = caller;
> +# ifdef __x86_64__
> +      asm volatile ("movq %0, %%rsp\n" /* Switch to new outermost stack.  */
> +                    "movq $0, %%rbp\n" /* Clear outermost frame pointer.  */
Unless you are intentionally preserving flags, `xorl %%ebp, %%ebp` is
better way to
zero a register.
> +                    "jmp *%1" : : "r" (data), "r" (&doinit1));
> +# else
>        asm volatile ("movl %0, %%esp\n" /* Switch to new outermost stack.  */
>                     "movl $0, %%ebp\n" /* Clear outermost frame pointer.  */
>                     "jmp *%1" : : "r" (data), "r" (&doinit1));
> +# endif
>        /* NOTREACHED */
>      }
>
> --
> 2.39.2
>