From 06f61af8025452514945657e9b4cb1c9ba8967c5 Mon Sep 17 00:00:00 2001 From: Fangrui Song Date: Tue, 19 Sep 2023 17:17:28 -0700 Subject: [PATCH] x86/speculation, objtool: Use absolute relocations for annotations 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 Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra (Intel) Cc: Josh Poimboeuf Link: https://lore.kernel.org/r/20230920001728.1439947-1-maskray@google.com Cc: Nathan Chancellor Signed-off-by: Greg Kroah-Hartman --- 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(-) diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h index 9c4da69..65f7909 100644 --- 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_reserved(void *start, void *end) .macro ANNOTATE_IGNORE_ALTERNATIVE .Lannotate_\@: .pushsection .discard.ignore_alts - .long .Lannotate_\@ - . + .long .Lannotate_\@ .popsection .endm diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 197ff4f..0396458 100644 --- 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]; diff --git a/include/linux/objtool.h b/include/linux/objtool.h index b5440e7..33212e9 100644 --- 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 -- 2.7.4