Re: [RFC PATCH 5/9] hurd: Simplify init-first.c a bit

[Samuel Thibault]

Applied, thanks!

Sergey Bugaev, le sam. 18 févr. 2023 23:37:13 +0300, a ecrit:
> And make it a bit more 64-bit ready. This is in preparation to moving this
> file into x86/
> 
> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
> ---
>  sysdeps/mach/hurd/i386/init-first.c | 23 +++++++----------------
>  1 file changed, 7 insertions(+), 16 deletions(-)
> 
> diff --git a/sysdeps/mach/hurd/i386/init-first.c 
> b/sysdeps/mach/hurd/i386/init-first.c
> index 94c94651..a558da16 100644
> --- a/sysdeps/mach/hurd/i386/init-first.c
> +++ b/sysdeps/mach/hurd/i386/init-first.c
> @@ -195,7 +195,7 @@ init (int *data)
>    /* Call `init1' (above) with the user code as the return address, and the
>       argument data immediately above that on the stack.  */
>  
> -  int usercode;
> +  void *usercode, **ret_address;
>  
>    void call_init1 (void);
>  
> @@ -206,10 +206,11 @@ init (int *data)
>       recognize that this read operation may alias the following write
>       operation, and thus is free to reorder the two, clobbering the
>       original return address.  */
> -  usercode = *((int *) __builtin_frame_address (0) + 1);
> +  ret_address = (void **) __builtin_frame_address (0) + 1;
> +  usercode = *ret_address;
>    /* GCC 4.4.6 also wants us to force loading USERCODE already here.  */
>    asm volatile ("# %0" : : "X" (usercode));
> -  *((void **) __builtin_frame_address (0) + 1) = &call_init1;
> +  *ret_address = &call_init1;
>    /* Force USERCODE into %eax and &init1 into %ecx, which are not
>       restored by function return.  */
>    asm volatile ("# a %0 c %1" : : "a" (usercode), "c" (&init1));
> @@ -223,19 +224,9 @@ init (int *data)
>  /* The return address of `init' above, was redirected to here, so at
>     this point our stack is unwound and callers' registers restored.
>     Only %ecx and %eax are call-clobbered and thus still have the
> -   values we set just above.  Fetch from there the new stack pointer
> -   we will run on, and jmp to the run-time address of `init1'; when it
> -   returns, it will run the user code with the argument data at the
> -   top of the stack.  */
> -asm ("switch_stacks:\n"
> -     "       movl %eax, %esp\n"
> -     "       jmp *%ecx");
> -
> -/* As in the stack-switching case, at this point our stack is unwound
> -   and callers' registers restored, and only %ecx and %eax communicate
> -   values from the lines above.  In this case 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.  */
> +   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.  */
>  asm ("call_init1:\n"
>       "       push %eax\n"
>       "       jmp *%ecx\n");
> -- 
> 2.39.2
> 
> 

-- 
Samuel
---
Pour une évaluation indépendante, transparente et rigoureuse !
Je soutiens la Commission d'Évaluation de l'Inria.