[PATCH v2] firmware_loader: Align .builtin_fw to 8

[Fangrui Song]

arm64 references the start address of .builtin_fw (__start_builtin_fw)
with a pair of R_AARCH64_ADR_PREL_PG_HI21/R_AARCH64_LDST64_ABS_LO12_NC
relocations. The compiler is allowed to emit the
R_AARCH64_LDST64_ABS_LO12_NC relocation because struct builtin_fw in
include/linux/firmware.h is 8-byte aligned.

The R_AARCH64_LDST64_ABS_LO12_NC relocation requires the address to be a
multiple of 8, which may not be the case if .builtin_fw is empty.
Unconditionally align .builtin_fw to fix the linker error. 32-bit
architectures could use ALIGN(4) but that would add unnecessary
complexity, so just use ALIGN(8).

Fixes: 5658c76 ("firmware: allow firmware files to be built into kernel image")
Link: https://github.com/ClangBuiltLinux/linux/issues/1204
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx>
Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

---
Change in v2:
* Use output section alignment instead of inappropriate ALIGN_FUNCTION()
---
 include/asm-generic/vmlinux.lds.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b2b3d81b1535..b97c628ad91f 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -459,7 +459,7 @@
 	}								\
 									\
 	/* Built-in firmware blobs */					\
-	.builtin_fw        : AT(ADDR(.builtin_fw) - LOAD_OFFSET) {	\
+	.builtin_fw : AT(ADDR(.builtin_fw) - LOAD_OFFSET) ALIGN(8) {	\
 		__start_builtin_fw = .;					\
 		KEEP(*(.builtin_fw))					\
 		__end_builtin_fw = .;					\
-- 
2.29.2.576.ga3fc446d84-goog