[PATCH 01/11] objtool: Generic annotation infrastructure

Peter Zijlstra
2023-12-04T09:40:16Z

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@infradead.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.
*/