linux-kernel - [PATCH v2] arch: fix broken BuildID for arm64 and riscv

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Date:   Tue, 27 Dec 2022 03:45:37 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-arch@...r.kernel.org, linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, Dennis Gilmore <dennis@...il.us>,
        Albert Ou <aou@...s.berkeley.edu>,
        Arnd Bergmann <arnd@...db.de>,
        Jisheng Zhang <jszhang@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: [PATCH v2] arch: fix broken BuildID for arm64 and riscv

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. 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.

Link: https://lore.kernel.org/lkml/CAABkxwuQoz1CTbyb57n0ZX65eSYiTonFCU8-LCQc=74D=xE=rA@mail.gmail.com/
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@...il.us>
Suggested-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

Changes in v2:
  - discard .note.GNU-stack before .notes because many architectures
    call DISCARDS at the end of their linker scripts

 include/asm-generic/vmlinux.lds.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index a94219e9916f..659bf3b31c91 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -891,7 +891,12 @@
 #define PRINTK_INDEX
 #endif
 
+/*
+ * Discard .note.GNU-stack, which is emitted as PROGBITS by the compiler.
+ * Otherwise, the type of .notes section would become PROGBITS instead of NOTES.
+ */
 #define NOTES								\
+	/DISCARD/ : { *(.note.GNU-stack) }				\
 	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
 		BOUNDED_SECTION_BY(.note.*, _notes)			\
 	} NOTES_HEADERS							\
-- 
2.34.1