From: Masahiro Yamada masahiroy@kernel.org
commit 99cb0d917ffa1ab628bb67364ca9b162c07699b1 upstream.
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=x... 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@ausil.us Suggested-by: Ard Biesheuvel ardb@kernel.org Signed-off-by: Masahiro Yamada masahiroy@kernel.org Acked-by: Palmer Dabbelt palmer@rivosinc.com [Tom: stable backport 5.15.y, 5.10.y, 5.4.y]
Though the above "Fixes:" commits are not in this kernel, the conditions which lead to a missing Build ID in arm64 vmlinux are similar.
Evidence points to these conditions: 1. ld version > 2.36 (exact binutils commit documented in a494398bde27) 2. first object which gets linked (head.o) has a PROGBITS .note.GNU-stack segment
These conditions can be observed when: - 5.15.60+ OR 5.10.136+ OR 5.4.210+ - AND ld version > 2.36 - AND arch=arm64 - AND CONFIG_MODVERSIONS=y
There are notable differences in the vmlinux elf files produced before(bad) and after(good) applying this series.
Good: p_type:PT_NOTE segment exists. Bad: p_type:PT_NOTE segment is missing.
Good: sh_name_str:.notes section has sh_type:SHT_NOTE Bad: sh_name_str:.notes section has sh_type:SHT_PROGBITS
`readelf -n` (as of v2.40) searches for Build Id by processing only the very first note in sh_type:SHT_NOTE sections.
This was previously bisected to the stable backport of 0d362be5b142. Follow-up experiments were discussed here: https://lore.kernel.org/all/20221221235413.xaisboqmr7dkqwn6@oracle.com/ which strongly hints at condition 2. Signed-off-by: Tom Saeger tom.saeger@oracle.com --- 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 e28792ca25a1..8471717c5085 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -903,7 +903,12 @@ #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) { \ __start_notes = .; \ KEEP(*(.note.*)) \