linux-kernel - Re: objtool "no non-local symbols" error with tip of tree LLVM

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Message-ID: <20220518012429.4zqzarvwsraxivux@treble>
Date:   Tue, 17 May 2022 18:24:29 -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: objtool "no non-local symbols" error with tip of tree LLVM

On Tue, May 17, 2022 at 05:42:04PM +0200, Peter Zijlstra wrote:
> +	for (;;) {
> +		symtab_data = elf_getdata(s, symtab_data);
> +		if (t)
> +			shndx_data = elf_getdata(t, shndx_data);
>  
> -	sym->idx = symtab->sh.sh_size / sizeof(sym->sym);
> -	elf_dirty_reloc_sym(elf, sym);
> +		if (!symtab_data) {
> +			if (!idx) {
> +				void *buf;

I'm confused by whatever this is doing, how is !symtab_data possible,
i.e. why would symtab not have data?

>  elf_create_section_symbol(struct elf *elf, struct section *sec)
>  {
>  	struct section *symtab, *symtab_shndx;
> -	Elf_Data *shndx_data = NULL;
> -	struct symbol *sym;
> -	Elf32_Word shndx;
> +	Elf32_Word first_non_local, new;
> +	struct symbol *sym, *old;
> +	int size;
> +
> +	if (elf->ehdr.e_ident[EI_CLASS] == ELFCLASS32)
> +		size = sizeof(Elf32_Sym);
> +	else
> +		size = sizeof(Elf64_Sym);

This should probably be called 'entsize' and I think you can just get it
from symtab->sh.sh_entsize.

> +	/*
> +	 * Either way, we added a LOCAL symbol.
> +	 */
> +	symtab->sh.sh_info += 1;
> +
>  	elf_add_symbol(elf, sym);

Not sure if it matters here, but elf_add_symbol() doesn't set sym->alias
and sym->pv_target, and both of those are unconditionally initialized in
read_symbols().  Should elf_add_symbol() be changed to initialize them?

-- 
Josh