From c5b1184decc819756ae549ba54c63b6790c4ddfd Mon Sep 17 00:00:00 2001 From: Tiezhu Yang Date: Tue, 24 Sep 2024 14:27:10 +0800 Subject: [PATCH] compiler.h: specify correct attribute for .rodata..c_jump_table 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 Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: [6.9+] Signed-off-by: Andrew Morton --- include/linux/compiler.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index ec55bcce4146..4d4e23b6e3e7 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -133,7 +133,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, #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()