[PATCH] arch: fix broken BuildID for arm64 and riscv

[Masahiro Yamada]

Dennis Gilmore reports that the BuildID is missing in the arm64 vmlinux
since commit 994b7ac1697b ("arm64: remove special treatment for the
link order of head.o").

The issue is that the type of .notes section, which contains the BuildID,
changed from NOTES to PROGBITS.

Ard Biesheuvel figured out that whichever object gets linked first gets
to decide the type of a section, and the PROGBITS type is the result of
the compiler emitting .note.GNU-stack as PROGBITS rather than NOTE.

While Ard provided a fix for arm64, I want to fix this globally because
the same issue is happening on riscv since commit 2348e6bf4421 ("riscv:
remove special treatment for the link order of head.o"). This problem
will happen in general for other architectures if they start to drop
unneeded entries from scripts/head-object-list.txt.

Discard .note.GNU-stack in include/asm-generic/vmlinux.lds.h.

riscv needs to change its linker script so that DISCARDS comes before
the .notes section.

Link: https://lore.kernel.org/lkml/CAABkxwuQoz1CTbyb57n0ZX65eSYiTonFCU8-LCQc=74D=xE=rA@xxxxxxxxxxxxxx/
Fixes: 994b7ac1697b ("arm64: remove special treatment for the link order of head.o")
Fixes: 2348e6bf4421 ("riscv: remove special treatment for the link order of head.o")
Reported-by: Dennis Gilmore <dennis@xxxxxxxx>
Suggested-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
---

 arch/riscv/kernel/vmlinux.lds.S   | 4 ++--
 include/asm-generic/vmlinux.lds.h | 1 +
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 4e6c88aa4d87..1865a258e560 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -31,6 +31,8 @@ PECOFF_FILE_ALIGNMENT = 0x200;
 
 SECTIONS
 {
+	DISCARDS
+
 	/* Beginning of code and text segment */
 	. = LOAD_OFFSET;
 	_start = .;
@@ -141,7 +143,5 @@ SECTIONS
 	STABS_DEBUG
 	DWARF_DEBUG
 	ELF_DETAILS
-
-	DISCARDS
 }
 #endif /* CONFIG_XIP_KERNEL */
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index a94219e9916f..2993b790fe98 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -1007,6 +1007,7 @@
 	*(.modinfo)							\
 	/* ld.bfd warns about .gnu.version* even when not emitted */	\
 	*(.gnu.version*)						\
+	*(.note.GNU-stack)	/* emitted as PROGBITS */
 
 #define DISCARDS							\
 	/DISCARD/ : {							\
-- 
2.34.1