From a7ce57ca9407dd257915b56acf970e80b6f04515 Mon Sep 17 00:00:00 2001
From: Joe Lawrence <joe.lawrence@redhat.com>
Date: Sun, 22 Aug 2021 18:50:36 -0400
Subject: [PATCH] objtool: Make .altinstructions section entry size consistent
Git-commit: dc02368164bd0ec603e3f5b3dd8252744a667b8a
Patch-mainline: v5.15-rc5
References: stable-5.14.12
[ Upstream commit dc02368164bd0ec603e3f5b3dd8252744a667b8a ]
Commit e31694e0a7a7 ("objtool: Don't make .altinstructions writable")
aligned objtool-created and kernel-created .altinstructions section
flags, but there remains a minor discrepency in their use of a section
entry size: objtool sets one while the kernel build does not.
While sh_entsize of sizeof(struct alt_instr) seems intuitive, this small
deviation can cause failures with external tooling (kpatch-build).
Fix this by creating new .altinstructions sections with sh_entsize of 0
and then later updating sec->sh_size as alternatives are added to the
section. An added benefit is avoiding the data descriptor and buffer
created by elf_create_section(), but previously unused by
elf_add_alternative().
Fixes: 9bc0bb50727c ("objtool/x86: Rewrite retpoline thunk calls")
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20210822225037.54620-2-joe.lawrence@redhat.com
Cc: Andy Lavr <andy.lavr@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
tools/objtool/arch/x86/decode.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index bc821056aba9..0893436cc09f 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -684,7 +684,7 @@ static int elf_add_alternative(struct elf *elf,
sec = find_section_by_name(elf, ".altinstructions");
if (!sec) {
sec = elf_create_section(elf, ".altinstructions",
- SHF_ALLOC, size, 0);
+ SHF_ALLOC, 0, 0);
if (!sec) {
WARN_ELF("elf_create_section");
--
2.26.2