6.6-stable review patch. If anyone has any objections, please let me know.
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From: Fangrui Song maskray@google.com
commit b8ec60e1186cdcfce41e7db4c827cb107e459002 upstream.
.discard.retpoline_safe sections do not have the SHF_ALLOC flag. These sections referencing text sections' STT_SECTION symbols with PC-relative relocations like R_386_PC32 [0] is conceptually not suitable. Newer LLD will report warnings for REL relocations even for relocatable links [1]:
ld.lld: warning: vmlinux.a(drivers/i2c/busses/i2c-i801.o):(.discard.retpoline_safe+0x120): has non-ABS relocation R_386_PC32 against symbol ''
Switch to absolute relocations instead, which indicate link-time addresses. In a relocatable link, these addresses are also output section offsets, used by checks in tools/objtool/check.c. When linking vmlinux, these .discard.* sections will be discarded, therefore it is not a problem that R_X86_64_32 cannot represent a kernel address.
Alternatively, we could set the SHF_ALLOC flag for .discard.* sections, but I think non-SHF_ALLOC for sections to be discarded makes more sense.
Note: if we decide to never support REL architectures (e.g. arm, i386), we can utilize R_*_NONE relocations (.reloc ., BFD_RELOC_NONE, sym), making .discard.* sections zero-sized. That said, the section content waste is 4 bytes per entry, much smaller than sizeof(Elf{32,64}_Rel).
[0] commit 1c0c1faf5692 ("objtool: Use relative pointers for annotations") [1] https://github.com/ClangBuiltLinux/linux/issues/1937
Signed-off-by: Fangrui Song maskray@google.com Signed-off-by: Ingo Molnar mingo@kernel.org Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Josh Poimboeuf jpoimboe@redhat.com Link: https://lore.kernel.org/r/20230920001728.1439947-1-maskray@google.com Cc: Nathan Chancellor nathan@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/alternative.h | 4 ++-- arch/x86/include/asm/nospec-branch.h | 4 ++-- include/linux/objtool.h | 10 +++++----- 3 files changed, 9 insertions(+), 9 deletions(-)
--- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -58,7 +58,7 @@ #define ANNOTATE_IGNORE_ALTERNATIVE \ "999:\n\t" \ ".pushsection .discard.ignore_alts\n\t" \ - ".long 999b - .\n\t" \ + ".long 999b\n\t" \ ".popsection\n\t"
/* @@ -352,7 +352,7 @@ static inline int alternatives_text_rese .macro ANNOTATE_IGNORE_ALTERNATIVE .Lannotate_@: .pushsection .discard.ignore_alts - .long .Lannotate_@ - . + .long .Lannotate_@ .popsection .endm
--- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -196,7 +196,7 @@ .macro ANNOTATE_RETPOLINE_SAFE .Lhere_@: .pushsection .discard.retpoline_safe - .long .Lhere_@ - . + .long .Lhere_@ .popsection .endm
@@ -334,7 +334,7 @@ #define ANNOTATE_RETPOLINE_SAFE \ "999:\n\t" \ ".pushsection .discard.retpoline_safe\n\t" \ - ".long 999b - .\n\t" \ + ".long 999b\n\t" \ ".popsection\n\t"
typedef u8 retpoline_thunk_t[RETPOLINE_THUNK_SIZE]; --- a/include/linux/objtool.h +++ b/include/linux/objtool.h @@ -48,13 +48,13 @@ #define ANNOTATE_NOENDBR \ "986: \n\t" \ ".pushsection .discard.noendbr\n\t" \ - ".long 986b - .\n\t" \ + ".long 986b\n\t" \ ".popsection\n\t"
#define ASM_REACHABLE \ "998:\n\t" \ ".pushsection .discard.reachable\n\t" \ - ".long 998b - .\n\t" \ + ".long 998b\n\t" \ ".popsection\n\t"
#else /* __ASSEMBLY__ */ @@ -66,7 +66,7 @@ #define ANNOTATE_INTRA_FUNCTION_CALL \ 999: \ .pushsection .discard.intra_function_calls; \ - .long 999b - .; \ + .long 999b; \ .popsection;
/* @@ -118,7 +118,7 @@ .macro ANNOTATE_NOENDBR .Lhere_@: .pushsection .discard.noendbr - .long .Lhere_@ - . + .long .Lhere_@ .popsection .endm
@@ -142,7 +142,7 @@ .macro REACHABLE .Lhere_@: .pushsection .discard.reachable - .long .Lhere_@ - . + .long .Lhere_@ .popsection .endm