Re: [Xen-devel] [PATCH v3 03/16] x86/boot: call reloc() using cdecl calling convention

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.04.16 at 14:33, <daniel.kiper@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/boot/reloc.c
> +++ b/xen/arch/x86/boot/reloc.c
> @@ -10,15 +10,25 @@
>   *    Keir Fraser <keir@xxxxxxx>
>   */
>  
> -/* entered with %eax = BOOT_TRAMPOLINE */
> +/*
> + * This entry point is entered from xen/arch/x86/boot/head.S with:
> + *   - 0x4(%esp) = MULTIBOOT_INFORMATION_ADDRESS,
> + *   - 0x8(%esp) = BOOT_TRAMPOLINE_ADDRESS.
> + */
>  asm (
>      "    .text                         \n"
>      "    .globl _start                 \n"
>      "_start:                           \n"
> +    "    push %ebp                     \n"
> +    "    mov  %esp,%ebp                \n"
>      "    call 1f                       \n"
> -    "1:  pop  %ebx                     \n"
> -    "    mov  %eax,alloc-1b(%ebx)      \n"
> -    "    jmp  reloc                    \n"
> +    "1:  pop  %ecx                     \n"
> +    "    mov  0xc(%ebp),%eax           \n"
> +    "    mov  %eax,alloc-1b(%ecx)      \n"
> +    "    push 0x8(%ebp)                \n"
> +    "    call reloc                    \n"
> +    "    leave                         \n"
> +    "    ret                           \n"
>      );

If Andrew's suggestion to remove this asm() altogether doesn't
work out, then I do not see justification for adding a frame
pointer here - addressing through %esp should be quite fine.
Which in turn would eliminate the need to convert jmp to call.

Jan


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