From: Vincent Mailhol <mailhol@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>,
Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
Vincent Mailhol <mailhol@kernel.org>
Subject: [PATCH 1/3] efi/libstub: move direct GUID references to static storage
Date: Thu, 03 Sep 2026 23:25:15 +0200 [thread overview]
Message-ID: <20260903-libstub_guid_cleanup-v1-1-06fcb6216975@kernel.org> (raw)
In-Reply-To: <20260903-libstub_guid_cleanup-v1-0-06fcb6216975@kernel.org>
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>
---
drivers/firmware/efi/libstub/gop.c | 17 ++++++++++-------
drivers/firmware/efi/libstub/smbios.c | 3 ++-
drivers/firmware/efi/libstub/x86-stub.c | 3 ++-
drivers/firmware/efi/libstub/zboot.c | 3 ++-
4 files changed, 16 insertions(+), 10 deletions(-)
diff --git a/drivers/firmware/efi/libstub/gop.c b/drivers/firmware/efi/libstub/gop.c
index 80dc8cfeb33e..acc2827ba4d7 100644
--- a/drivers/firmware/efi/libstub/gop.c
+++ b/drivers/firmware/efi/libstub/gop.c
@@ -425,6 +425,8 @@ static void setup_edid_info(struct edid_info *edid, u32 gop_size_of_edid, u8 *go
static efi_handle_t find_handle_with_primary_gop(unsigned long num, const efi_handle_t handles[],
efi_graphics_output_protocol_t **found_gop)
{
+ static efi_guid_t graphics_output_guid = EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID;
+ static efi_guid_t console_out_device_guid = EFI_CONSOLE_OUT_DEVICE_GUID;
efi_graphics_output_protocol_t *first_gop;
efi_handle_t h, first_gop_handle;
@@ -439,8 +441,7 @@ static efi_handle_t find_handle_with_primary_gop(unsigned long num, const efi_ha
efi_graphics_output_mode_info_t *info;
void *dummy = NULL;
- status = efi_bs_call(handle_protocol, h,
- &EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID,
+ status = efi_bs_call(handle_protocol, h, &graphics_output_guid,
(void **)&gop);
if (status != EFI_SUCCESS)
continue;
@@ -462,7 +463,7 @@ static efi_handle_t find_handle_with_primary_gop(unsigned long num, const efi_ha
* don't bother looking any further.
*/
status = efi_bs_call(handle_protocol, h,
- &EFI_CONSOLE_OUT_DEVICE_GUID, &dummy);
+ &console_out_device_guid, &dummy);
if (status == EFI_SUCCESS) {
if (found_gop)
*found_gop = gop;
@@ -480,6 +481,9 @@ static efi_handle_t find_handle_with_primary_gop(unsigned long num, const efi_ha
efi_status_t efi_setup_graphics(struct screen_info *si, struct edid_info *edid)
{
+ static efi_guid_t graphics_output_guid = EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID;
+ static efi_guid_t edid_active_guid = EFI_EDID_ACTIVE_PROTOCOL_GUID;
+ static efi_guid_t edid_discovered_guid = EFI_EDID_DISCOVERED_PROTOCOL_GUID;
efi_handle_t *handles __free(efi_pool) = NULL;
efi_handle_t handle;
efi_graphics_output_protocol_t *gop;
@@ -487,8 +491,7 @@ efi_status_t efi_setup_graphics(struct screen_info *si, struct edid_info *edid)
unsigned long num;
status = efi_bs_call(locate_handle_buffer, EFI_LOCATE_BY_PROTOCOL,
- &EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID, NULL, &num,
- &handles);
+ &graphics_output_guid, NULL, &num, &handles);
if (status != EFI_SUCCESS)
return status;
@@ -510,14 +513,14 @@ efi_status_t efi_setup_graphics(struct screen_info *si, struct edid_info *edid)
u32 gop_size_of_edid = 0;
u8 *gop_edid = NULL;
- status = efi_bs_call(handle_protocol, handle, &EFI_EDID_ACTIVE_PROTOCOL_GUID,
+ status = efi_bs_call(handle_protocol, handle, &edid_active_guid,
(void **)&active_edid);
if (status == EFI_SUCCESS) {
gop_size_of_edid = efi_table_attr(active_edid, size_of_edid);
gop_edid = efi_table_attr(active_edid, edid);
} else {
status = efi_bs_call(handle_protocol, handle,
- &EFI_EDID_DISCOVERED_PROTOCOL_GUID,
+ &edid_discovered_guid,
(void **)&discovered_edid);
if (status == EFI_SUCCESS) {
gop_size_of_edid = efi_table_attr(discovered_edid, size_of_edid);
diff --git a/drivers/firmware/efi/libstub/smbios.c b/drivers/firmware/efi/libstub/smbios.c
index f31410d7e7e1..efbbfc3c2c0d 100644
--- a/drivers/firmware/efi/libstub/smbios.c
+++ b/drivers/firmware/efi/libstub/smbios.c
@@ -35,12 +35,13 @@ union efi_smbios_protocol {
const struct efi_smbios_record *efi_get_smbios_record(u8 type)
{
+ static efi_guid_t smbios_guid = EFI_SMBIOS_PROTOCOL_GUID;
struct efi_smbios_record *record;
efi_smbios_protocol_t *smbios;
efi_status_t status;
u16 handle = 0xfffe;
- status = efi_bs_call(locate_protocol, &EFI_SMBIOS_PROTOCOL_GUID, NULL,
+ status = efi_bs_call(locate_protocol, &smbios_guid, NULL,
(void **)&smbios) ?:
efi_call_proto(smbios, get_next, &handle, &type, &record, NULL);
if (status != EFI_SUCCESS)
diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index cef32e2c82d8..cb0abe13a6c4 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -335,6 +335,7 @@ static bool apple_match_product_name(void)
static void apple_set_os(void)
{
+ static efi_guid_t apple_set_os_guid = APPLE_SET_OS_PROTOCOL_GUID;
struct {
unsigned long version;
efi_status_t (__efiapi *set_os_version)(const char *);
@@ -345,7 +346,7 @@ static void apple_set_os(void)
if (!efi_is_64bit() || !apple_match_product_name())
return;
- status = efi_bs_call(locate_protocol, &APPLE_SET_OS_PROTOCOL_GUID, NULL,
+ status = efi_bs_call(locate_protocol, &apple_set_os_guid, NULL,
(void **)&set_os);
if (status != EFI_SUCCESS)
return;
diff --git a/drivers/firmware/efi/libstub/zboot.c b/drivers/firmware/efi/libstub/zboot.c
index 4b76f74c56da..4a5ffe164873 100644
--- a/drivers/firmware/efi/libstub/zboot.c
+++ b/drivers/firmware/efi/libstub/zboot.c
@@ -34,6 +34,7 @@ struct sysfb_display_info *alloc_primary_display(void)
asmlinkage efi_status_t __efiapi
efi_zboot_entry(efi_handle_t handle, efi_system_table_t *systab)
{
+ static efi_guid_t loaded_image_guid = LOADED_IMAGE_PROTOCOL_GUID;
char *cmdline_ptr __free(efi_pool) = NULL;
unsigned long image_base, alloc_size;
efi_loaded_image_t *image;
@@ -42,7 +43,7 @@ efi_zboot_entry(efi_handle_t handle, efi_system_table_t *systab)
WRITE_ONCE(efi_system_table, systab);
status = efi_bs_call(handle_protocol, handle,
- &LOADED_IMAGE_PROTOCOL_GUID, (void **)&image);
+ &loaded_image_guid, (void **)&image);
if (status != EFI_SUCCESS) {
efi_err("Failed to locate parent's loaded image protocol\n");
return status;
--
2.55.0
next prev parent reply other threads:[~2026-09-03 21:25 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-03 21:25 [PATCH 0/3] efi/libstub: reduce size by optimizing GUID storage Vincent Mailhol
2026-09-03 21:25 ` Vincent Mailhol [this message]
2026-09-03 21:25 ` [PATCH 2/3] efi/libstub: make local GUID variables static Vincent Mailhol
2026-09-03 21:25 ` [PATCH 3/3] efi/libstub: factor shared static GUID variables Vincent Mailhol
2026-09-04 16:31 ` [PATCH 0/3] efi/libstub: reduce size by optimizing GUID storage Ard Biesheuvel
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