efi/libstub: move direct GUID references to static storage

Some EFI stub call sites pass the address of a GUID macro directly to
EFI boot services. With gcc, this makes the compiler materialize the
GUID data at the call site, which is wasteful in the size-sensitive EFI
stub.

For example, consider this program:

	#include <linux/efi.h>

	#define GUID							\
		EFI_GUID(0xaaaaaaaa, 0xbbbb, 0xcccc,			\
			 0xdd, 0xdd, 0xdd, 0xdd, 0xdd, 0xdd, 0xdd, 0xdd)

	void foo(const efi_guid_t *guid);

	void guid_direct(void)
	{
		foo(&GUID);
	}

	void guid_static(void)
	{
		static efi_guid_t guid = GUID;

		foo(&guid);
	}

For guid_direct(), gcc materializes the GUID on the stack:

   0:	f3 0f 1e fa          	endbr64
   4:	48 b8 aa aa aa aa bb 	movabs $0xccccbbbbaaaaaaaa,%rax
   b:	bb cc cc
   e:	48 83 ec 18          	sub    $0x18,%rsp
  12:	48 89 04 24          	mov    %rax,(%rsp)
  16:	48 89 e7             	mov    %rsp,%rdi
  19:	48 b8 dd dd dd dd dd 	movabs $0xdddddddddddddddd,%rax
  20:	dd dd dd
  23:	48 89 44 24 08       	mov    %rax,0x8(%rsp)
  28:	e8 00 00 00 00       	call   2d <guid_direct+0x2d>
  2d:	48 83 c4 18          	add    $0x18,%rsp
  31:	c3                   	ret

For guid_static(), gcc stores the GUID in .data and emits a RIP-relative
address load:

  32:	f3 0f 1e fa          	endbr64
  36:	48 8d 3d 00 00 00 00 	lea    0x0(%rip),%rdi
  3d:	e9 00 00 00 00       	jmp    42 <guid_static+0x10>

Overall, guid_direct() consumes 50 bytes in the .text segment whereas
guid_static() needs only 32 bytes in total: 16 bytes in .data and 16
bytes in .text.

Move these direct GUID references to function-local static objects and
pass their address instead. EFI boot service prototypes take non-const
efi_guid_t pointers, so keep the GUID non-const to prevent a
-Wdiscarded-qualifiers warning.

For an x86_64 build with gcc 15.3.0, bloat-o-meter reports:

  add/remove: 6/0 grow/shrink: 0/3 up/down: 112/-458 (-346)
  Function                                     old     new   delta
  graphics_output_guid                           -      32     +32
  smbios_guid                                    -      16     +16
  edid_discovered_guid                           -      16     +16
  edid_active_guid                               -      16     +16
  console_out_device_guid                        -      16     +16
  apple_set_os_guid                              -      16     +16
  efi_stub_entry                              4180    4136     -44
  efi_get_smbios_record                        283     226     -57
  efi_setup_graphics                          2210    1853    -357
  Total: Before=29223, After=28877, chg -1.18%

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

0 files changed, 0 insertions, 0 deletions