linux-kernel - Re: [PATCH] objtool: support symtab

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Date:   Fri, 4 Sep 2020 09:54:29 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] objtool: support symtab_shndx during dump

On Thu, 3 Sep 2020, Josh Poimboeuf wrote:

> On Wed, Aug 12, 2020 at 10:57:11AM -0700, Kristen Carlson Accardi wrote:
> 
> >  			if (GELF_ST_TYPE(sym.st_info) == STT_SECTION) {
> > -				scn = elf_getscn(elf, sym.st_shndx);
> > +				if ((sym.st_shndx > SHN_UNDEF &&
> > +				     sym.st_shndx < SHN_LORESERVE) ||
> > +				    (xsymtab && sym.st_shndx == SHN_XINDEX)) {
> > +					if (sym.st_shndx != SHN_XINDEX)
> > +						shndx = sym.st_shndx;
> 
> The sym.st_shndx checks are redundant, if 'sym.st_shndx == SHN_XINDEX'
> then 'sym.st_shndx != SHN_XINDEX' can't be true.

It is probably a copy-paste from read_symbols() in elf.c, where the logic 
is different.

> Actually I think this can be even further simplified to something like
> 
> 				if (!shndx)
> 					shndx = sym.st_shndx;

This relies on the fact that gelf_getsymshndx() always initializes shndx, 
no? I think it would be better to initialize it in orc_dump() too. Safer 
and easier to read. It applies to Kristen's patch as well. I missed that.

Miroslav