The patch titled Subject: compiler.h: specify correct attribute for .rodata..c_jump_table has been added to the -mm mm-hotfixes-unstable branch. Its filename is compilerh-specify-correct-attribute-for-rodatac_jump_table.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Tiezhu Yang yangtiezhu@loongson.cn Subject: compiler.h: specify correct attribute for .rodata..c_jump_table Date: Tue, 24 Sep 2024 14:27:10 +0800

Currently, there is an assembler message when generating kernel/bpf/core.o under CONFIG_OBJTOOL with LoongArch compiler toolchain:

Warning: setting incorrect section attributes for .rodata..c_jump_table

This is because the section ".rodata..c_jump_table" should be readonly, but there is a "W" (writable) part of the flags:

$ readelf -S kernel/bpf/core.o | grep -A 1 "rodata..c" [34] .rodata..c_j[...] PROGBITS 0000000000000000 0000d2e0 0000000000000800 0000000000000000 WA 0 0 8

There is no above issue on x86 due to the generated section flag is only "A" (allocatable). In order to silence the warning on LoongArch, specify the attribute like ".rodata..c_jump_table,"a",@progbits #" explicitly, then the section attribute of ".rodata..c_jump_table" must be readonly in the kernel/bpf/core.o file.

Before:

$ objdump -h kernel/bpf/core.o | grep -A 1 "rodata..c" 21 .rodata..c_jump_table 00000800 0000000000000000 0000000000000000 0000d2e0 2**3 CONTENTS, ALLOC, LOAD, RELOC, DATA

After:

$ objdump -h kernel/bpf/core.o | grep -A 1 "rodata..c" 21 .rodata..c_jump_table 00000800 0000000000000000 0000000000000000 0000d2e0 2**3 CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA

By the way, AFAICT, maybe the root cause is related with the different compiler behavior of various archs, so to some extent this change is a workaround for LoongArch, and also there is no effect for x86 which is the only port supported by objtool before LoongArch with this patch.

Link: https://lkml.kernel.org/r/20240924062710.1243-1-yangtiezhu@loongson.cn Signed-off-by: Tiezhu Yang yangtiezhu@loongson.cn Cc: Josh Poimboeuf jpoimboe@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: stable@vger.kernel.org [6.9+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/compiler.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/compiler.h~compilerh-specify-correct-attribute-for-rodatac_jump_table +++ a/include/linux/compiler.h @@ -133,7 +133,7 @@ void ftrace_likely_update(struct ftrace_ #define annotate_unreachable() __annotate_unreachable(__COUNTER__)

/* Annotate a C jump table to allow objtool to follow the code flow */ -#define __annotate_jump_table __section(".rodata..c_jump_table") +#define __annotate_jump_table __section(".rodata..c_jump_table,"a",@progbits #")

#else /* !CONFIG_OBJTOOL */ #define annotate_reachable() _

Patches currently in -mm which might be from yangtiezhu@loongson.cn are

compilerh-specify-correct-attribute-for-rodatac_jump_table.patch