linux-kernel - [PATCH 01/11] objtool: Generic annotation infrastructure

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Message-Id: <20231204093731.356358182@infradead.org>
Date:   Mon, 04 Dec 2023 10:37:03 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org, x86@...nel.org,
        kvm@...r.kernel.org
Subject: [PATCH 01/11] objtool: Generic annotation infrastructure

Avoid endless .discard.foo sections for each annotation, create a
single .discard.annotate section that takes an annotation type along
with the instruction.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
--- a/include/linux/objtool.h
+++ b/include/linux/objtool.h
@@ -57,6 +57,13 @@
 	".long 998b\n\t"						\
 	".popsection\n\t"
 
+#define ASM_ANNOTATE(x)						\
+	"911:\n\t"						\
+	".pushsection .discard.annotate,\"M\",@progbits,8\n\t"	\
+	".long 911b - .\n\t"					\
+	".long " __stringify(x) "\n\t"				\
+	".popsection\n\t"
+
 #else /* __ASSEMBLY__ */
 
 /*
@@ -146,6 +153,14 @@
 	.popsection
 .endm
 
+.macro ANNOTATE type:req
+.Lhere_\@:
+	.pushsection .discard.annotate,"M",@progbits,8
+	.long	.Lhere_\@ - .
+	.long	\type
+	.popsection
+.endm
+
 #endif /* __ASSEMBLY__ */
 
 #else /* !CONFIG_OBJTOOL */
@@ -167,6 +182,8 @@
 .endm
 .macro REACHABLE
 .endm
+.macro ANNOTATE
+.endm
 #endif
 
 #endif /* CONFIG_OBJTOOL */
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2308,6 +2308,41 @@ static int read_unwind_hints(struct objt
 	return 0;
 }
 
+static int read_annotate(struct objtool_file *file, void (*func)(int type, struct instruction *insn))
+{
+	struct section *rsec, *sec;
+	struct instruction *insn;
+	struct reloc *reloc;
+	int type;
+
+	rsec = find_section_by_name(file->elf, ".rela.discard.annotate");
+	if (!rsec)
+		return 0;
+
+	sec = find_section_by_name(file->elf, ".discard.annotate");
+	if (!sec)
+		return 0;
+
+	for_each_reloc(rsec, reloc) {
+		insn = find_insn(file, reloc->sym->sec,
+				 reloc->sym->offset + reloc_addend(reloc));
+		if (!insn) {
+			WARN("bad .discard.annotate entry: %d", reloc_idx(reloc));
+			return -1;
+		}
+
+		type = *(u32 *)(sec->data->d_buf + (reloc_idx(reloc) * sec->sh.sh_entsize) + 4);
+
+		func(type, insn);
+	}
+
+	return 0;
+}
+
+static void __annotate_nop(int type, struct instruction *insn)
+{
+}
+
 static int read_noendbr_hints(struct objtool_file *file)
 {
 	struct instruction *insn;
@@ -2602,6 +2637,8 @@ static int decode_sections(struct objtoo
 	if (ret)
 		return ret;
 
+	ret = read_annotate(file, __annotate_nop);
+
 	/*
 	 * Must be before read_unwind_hints() since that needs insn->noendbr.
 	 */