linux-kernel - Re: [PATCH 5/9] objtool: Rework rebuild

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Date:   Tue, 16 Mar 2021 22:34:17 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, jgross@...e.com, mbenes@...e.cz,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/9] objtool: Rework rebuild_reloc logic

On Fri, Mar 12, 2021 at 06:16:18PM +0100, Peter Zijlstra wrote:
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -479,6 +479,8 @@ void elf_add_reloc(struct elf *elf, stru
>  
>  	list_add_tail(&reloc->list, &sec->reloc_list);
>  	elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));
> +
> +	sec->rereloc = true;
>  }

Can we just reuse sec->changed for this?  Something like this on top
(untested of course):

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index addcec88ac9f..b9cb74a54681 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -480,7 +480,7 @@ void elf_add_reloc(struct elf *elf, struct reloc *reloc)
 	list_add_tail(&reloc->list, &sec->reloc_list);
 	elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));
 
-	sec->rereloc = true;
+	sec->changed = true;
 }
 
 static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
@@ -882,9 +882,6 @@ int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
 	struct reloc *reloc;
 	int nr;
 
-	sec->changed = true;
-	elf->changed = true;
-
 	nr = 0;
 	list_for_each_entry(reloc, &sec->reloc_list, list)
 		nr++;
@@ -894,8 +891,6 @@ int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
 	case SHT_RELA: return elf_rebuild_rela_reloc_section(sec, nr);
 	default:       return -1;
 	}
-
-	sec->rereloc = false;
 }
 
 int elf_write_insn(struct elf *elf, struct section *sec,
@@ -950,14 +945,15 @@ int elf_write(struct elf *elf)
 	struct section *sec;
 	Elf_Scn *s;
 
-	list_for_each_entry(sec, &elf->sections, list) {
-		if (sec->reloc && sec->reloc->rereloc)
-			elf_rebuild_reloc_section(elf, sec->reloc);
-	}
-
-	/* Update section headers for changed sections: */
+	/* Update changed relocation sections and section headers: */
 	list_for_each_entry(sec, &elf->sections, list) {
 		if (sec->changed) {
+			if (sec->reloc &&
+			    elf_rebuild_reloc_section(elf, sec->reloc)) {
+				WARN_ELF("elf_rebuild_reloc_section");
+				return -1;
+			}
+
 			s = elf_getscn(elf->elf, sec->idx);
 			if (!s) {
 				WARN_ELF("elf_getscn");
@@ -969,6 +965,7 @@ int elf_write(struct elf *elf)
 			}
 
 			sec->changed = false;
+			elf->changed = true;
 		}
 	}
 
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 9fdd4c5f9f32..e6890cc70a25 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -39,7 +39,7 @@ struct section {
 	char *name;
 	int idx;
 	unsigned int len;
-	bool changed, text, rodata, noinstr, rereloc;
+	bool changed, text, rodata, noinstr;
 };
 
 struct symbol {