lkml.org 
[lkml]   [2020]   [Mar]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH 3/5] efi/x86: Make efi32_pe_entry more readable
On Mon, 2 Mar 2020 at 00:04, Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> Setup a proper frame pointer in efi32_pe_entry so that it's easier to
> calculate offsets for arguments.
>
> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
> ---
> arch/x86/boot/compressed/head_64.S | 57 +++++++++++++++++++++---------
> 1 file changed, 40 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index 920daf62dac2..fabbd4c2e9f2 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -658,42 +658,65 @@ SYM_DATA(efi_is64, .byte 1)
> .text
> .code32
> SYM_FUNC_START(efi32_pe_entry)
> +/*
> + * efi_status_t efi32_pe_entry(efi_handle_t image_handle,
> + * efi_system_table_32_t *sys_table)
> + */
> +
> pushl %ebp
> + movl %esp, %ebp
> + pushl %eax // dummy push to allocate loaded_image
>
> - pushl %ebx
> + pushl %ebx // save callee-save registers
> pushl %edi
> +
> call verify_cpu // check for long mode support
> - popl %edi
> - popl %ebx
> testl %eax, %eax
> movl $0x80000003, %eax // EFI_UNSUPPORTED
> - jnz 3f
> + jnz 2f
>
> call 1f
> -1: pop %ebp
> - subl $1b, %ebp
> +1: pop %ebx
> + subl $1b, %ebx
>
> /* Get the loaded image protocol pointer from the image handle */
> - subl $12, %esp // space for the loaded image pointer
> - pushl %esp // pass its address
> - leal loaded_image_proto(%ebp), %eax
> + leal -4(%ebp), %eax
> + pushl %eax // &loaded_image
> + leal loaded_image_proto(%ebx), %eax
> pushl %eax // pass the GUID address
> - pushl 28(%esp) // pass the image handle
> + pushl 8(%ebp) // pass the image handle
>
> - movl 36(%esp), %eax // sys_table
> + /*
> + * Note the alignment of the stack frame.
> + * sys_table
> + * handle <-- 16-byte aligned on entry by ABI
> + * return address
> + * frame pointer
> + * loaded_image <-- local variable
> + * saved %ebx <-- 16-byte aligned here
> + * saved %edi
> + * &loaded_image
> + * &loaded_image_proto
> + * handle <-- 16-byte aligned for call to handle_protocol
> + */
> +
> + movl 12(%ebp), %eax // sys_table
> movl ST32_boottime(%eax), %eax // sys_table->boottime
> call *BS32_handle_protocol(%eax) // sys_table->boottime->handle_protocol
> - cmp $0, %eax
> + addl $12, %esp // restore argument space
> + testl %eax, %eax
> jnz 2f
>
> - movl 32(%esp), %ecx // image_handle
> - movl 36(%esp), %edx // sys_table
> - movl 12(%esp), %esi // loaded_image
> + movl 8(%ebp), %ecx // image_handle
> + movl 12(%ebp), %edx // sys_table
> + movl -4(%ebp), %esi // loaded_image
> movl LI32_image_base(%esi), %esi // loaded_image->image_base
> + movl %ebx, %ebp // startup_32 for efi32_pe_stub_entry

The code that follows efi32_pe_stub_entry still expects the runtime
displacement in %ebp, so we'll need to pass that in another way here.

> jmp efi32_pe_stub_entry
>
> -2: addl $24, %esp
> -3: popl %ebp
> +2: popl %edi // restore callee-save registers
> + popl %ebx
> + leave
> ret
> SYM_FUNC_END(efi32_pe_entry)
>
> --
> 2.24.1
>

\
 
 \ /
  Last update: 2020-03-02 08:49    [W:0.082 / U:0.320 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site