linux-kernel - Re: [PATCH] objtool: Fix symbol creation

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Message-ID: <20220518173604.7gcrjjum6fo2m2ub@treble>
Date:   Wed, 18 May 2022 10:36:04 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com
Subject: Re: [PATCH] objtool: Fix symbol creation

On Wed, May 18, 2022 at 09:41:52AM +0200, Peter Zijlstra wrote:
> +static int elf_update_symbol(struct elf *elf, struct section *symtab,
> +			     struct section *symtab_shndx, struct symbol *sym)
>  {
> -	Elf_Data *data, *shndx_data = NULL;
> -	Elf32_Word first_non_local;
> -	struct symbol *sym;
> -	Elf_Scn *s;
> -
> -	first_non_local = symtab->sh.sh_info;
> -
> -	sym = find_symbol_by_index(elf, first_non_local);
> -	if (!sym) {
> -		WARN("no non-local symbols !?");
> -		return first_non_local;
> -	}
> +	Elf_Data *symtab_data = NULL, *shndx_data = NULL;
> +	Elf64_Xword entsize = symtab->sh.sh_entsize;
> +	Elf32_Word shndx = sym->sec->idx;

So if it's a global UNDEF symbol then I think 'sym->sec' can be NULL and
this blows up?

> +	for (;;) {
> +		/* get next data descriptor for the relevant sections */
> +		symtab_data = elf_getdata(s, symtab_data);
> +		if (t)
> +			shndx_data = elf_getdata(t, shndx_data);
> +
> +		/* end-of-list */
> +		if (!symtab_data) {
> +			/* if @idx == 0, it's the next contiguous entry, create it */
> +			if (!idx) {
> +				void *buf;

Could just do the "index out of range warning" here to reduce the
indentation level.

> +	/* setup extended section index magic and write the symbol */
> +	if (shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) {

> +		sym->sym.st_shndx = shndx;
> +		if (!shndx_data)
> +			shndx = 0;

I think this '0' is SHN_UNDEF?

Also shouldn't 'sym->sym.st_shndx' get the same value?

-- 
Josh