linux-kernel - [PATCH v2 06/16] objtool: Convert ANNOTATE_IGNORE

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Message-ID: <20241128094311.465691316@infradead.org>
Date: Thu, 28 Nov 2024 10:38:57 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: jpoimboe@...nel.org
Cc: chenhuacai@...nel.org,
 kernel@...0n.name,
 x86@...nel.org,
 peterz@...radead.org,
 loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: [PATCH v2 06/16] objtool: Convert ANNOTATE_IGNORE_ALTERNATIVE to ANNOTATE


Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/alternative.h  |   14 ++---------
 include/linux/objtool_types.h       |    1 
 tools/include/linux/objtool_types.h |    1 
 tools/objtool/check.c               |   45 ++++++++----------------------------
 4 files changed, 15 insertions(+), 46 deletions(-)

--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -4,6 +4,7 @@
 
 #include <linux/types.h>
 #include <linux/stringify.h>
+#include <linux/objtool.h>
 #include <asm/asm.h>
 
 #define ALT_FLAGS_SHIFT		16
@@ -58,11 +59,7 @@
  * objtool annotation to ignore the alternatives and only consider the original
  * instruction(s).
  */
-#define ANNOTATE_IGNORE_ALTERNATIVE				\
-	"999:\n\t"						\
-	".pushsection .discard.ignore_alts\n\t"			\
-	".long 999b\n\t"					\
-	".popsection\n\t"
+#define ANNOTATE_IGNORE_ALTERNATIVE	ASM_ANNOTATE(ANNOTYPE_IGNORE_ALTS)
 
 /*
  * The patching flags are part of the upper bits of the @ft_flags parameter when
@@ -314,12 +311,7 @@ void nop_func(void);
  * objtool annotation to ignore the alternatives and only consider the original
  * instruction(s).
  */
-.macro ANNOTATE_IGNORE_ALTERNATIVE
-	.Lannotate_\@:
-	.pushsection .discard.ignore_alts
-	.long .Lannotate_\@
-	.popsection
-.endm
+#define ANNOTATE_IGNORE_ALTERNATIVE ANNOTATE type=ANNOTYPE_IGNORE_ALTS
 
 /*
  * Issue one struct alt_instr descriptor entry (need to put it into
--- a/include/linux/objtool_types.h
+++ b/include/linux/objtool_types.h
@@ -62,5 +62,6 @@ struct unwind_hint {
 #define ANNOTYPE_INSTR_BEGIN		3
 #define ANNOTYPE_INSTR_END		4
 #define ANNOTYPE_UNRET_BEGIN		5
+#define ANNOTYPE_IGNORE_ALTS		6
 
 #endif /* _LINUX_OBJTOOL_TYPES_H */
--- a/tools/include/linux/objtool_types.h
+++ b/tools/include/linux/objtool_types.h
@@ -62,5 +62,6 @@ struct unwind_hint {
 #define ANNOTYPE_INSTR_BEGIN		3
 #define ANNOTYPE_INSTR_END		4
 #define ANNOTYPE_UNRET_BEGIN		5
+#define ANNOTYPE_IGNORE_ALTS		6
 
 #endif /* _LINUX_OBJTOOL_TYPES_H */
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1310,40 +1310,6 @@ static void add_uaccess_safe(struct objt
 }
 
 /*
- * FIXME: For now, just ignore any alternatives which add retpolines.  This is
- * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
- * But it at least allows objtool to understand the control flow *around* the
- * retpoline.
- */
-static int add_ignore_alternatives(struct objtool_file *file)
-{
-	struct section *rsec;
-	struct reloc *reloc;
-	struct instruction *insn;
-
-	rsec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
-	if (!rsec)
-		return 0;
-
-	for_each_reloc(rsec, reloc) {
-		if (reloc->sym->type != STT_SECTION) {
-			WARN("unexpected relocation symbol type in %s", rsec->name);
-			return -1;
-		}
-
-		insn = find_insn(file, reloc->sym->sec, reloc_addend(reloc));
-		if (!insn) {
-			WARN("bad .discard.ignore_alts entry");
-			return -1;
-		}
-
-		insn->ignore_alts = true;
-	}
-
-	return 0;
-}
-
-/*
  * Symbols that replace INSN_CALL_DYNAMIC, every (tail) call to such a symbol
  * will be added to the .retpoline_sites section.
  */
@@ -2414,6 +2380,15 @@ static int read_annotate(struct objtool_
 	return 0;
 }
 
+static int __annotate_ignore_alts(int type, struct instruction *insn)
+{
+	if (type != ANNOTYPE_IGNORE_ALTS)
+		return 0;
+
+	insn->ignore_alts = true;
+	return 0;
+}
+
 static int __annotate_noendbr(int type, struct instruction *insn)
 {
 	if (type != ANNOTYPE_NOENDBR)
@@ -2626,7 +2601,7 @@ static int decode_sections(struct objtoo
 	add_ignores(file);
 	add_uaccess_safe(file);
 
-	ret = add_ignore_alternatives(file);
+	ret = read_annotate(file, __annotate_ignore_alts);
 	if (ret)
 		return ret;