linux-kernel - Re: [RFC][PATCH 1/3] objtool: Clean up elf

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Date:   Tue, 16 Jun 2020 10:32:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Matt Helsley <mhelsley@...are.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org, dvyukov@...gle.com,
        elver@...gle.com, andreyknvl@...gle.com, mark.rutland@....com,
        rostedt@...dmis.org, jthierry@...hat.com, mbenes@...e.cz
Subject: Re: [RFC][PATCH 1/3] objtool: Clean up elf_write() condition

On Mon, Jun 15, 2020 at 08:44:11PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 15, 2020 at 11:34:48AM -0700, Matt Helsley wrote:
> > On Fri, Jun 12, 2020 at 04:30:35PM +0200, Peter Zijlstra wrote:
> > > With there being multiple ways to change the ELF data, let's more
> > > concisely track modification.
> > > 
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > 
> > Would it make sense to set the relocation section's "changed" flag in
> > addition to the elf struct's changed flag in elf_rebuild_reloc_section()?
> > 
> > Right now I think the code is  assuming that it's a newly created section
> > but it would be more defensive to set it during a rebuild too I think.
> 
> Indeed, currently the code assumes (and this is so) elf_rebuild_rela_sections()
> is only called on an elf_create_reloc_section() result and thus setting
> ->changed is superfluous.
> 
> But sure, I can certainly set them there too.

Delta to the patch.

---
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2740,7 +2740,7 @@ int check(const char *_objname, bool orc
 
 	objname = _objname;
 
-	file.elf = elf_open_read(objname, orc ? O_RDWR : O_RDONLY);
+	file.elf = elf_open_read(objname, O_RDWR);
 	if (!file.elf)
 		return 1;
 
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -849,11 +849,14 @@ static int elf_rebuild_rela_section(stru
 	return 0;
 }
 
-int elf_rebuild_reloc_section(struct section *sec)
+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++;
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -134,7 +134,7 @@ struct reloc *find_reloc_by_dest(const s
 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
 				     unsigned long offset, unsigned int len);
 struct symbol *find_func_containing(struct section *sec, unsigned long offset);
-int elf_rebuild_reloc_section(struct section *sec);
+int elf_rebuild_reloc_section(struct elf *elf, struct section *sec);
 
 #define for_each_sec(file, sec)						\
 	list_for_each_entry(sec, &file->elf->sections, list)
--- a/tools/objtool/orc_gen.c
+++ b/tools/objtool/orc_gen.c
@@ -222,7 +222,7 @@ int create_orc_sections(struct objtool_f
 		}
 	}
 
-	if (elf_rebuild_reloc_section(ip_relocsec))
+	if (elf_rebuild_reloc_section(file->elf, ip_relocsec))
 		return -1;
 
 	return 0;