linux-kernel - Re: [PATCH 3/5] objtool: Support Clang non-section symbols in ORC generation

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Message-ID: <20200401184953.GZ20730@hirez.programming.kicks-ass.net>
Date:   Wed, 1 Apr 2020 20:49:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Miroslav Benes <mbenes@...e.cz>,
        Julien Thierry <jthierry@...hat.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Dmitry Golovin <dima@...ovin.in>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: Re: [PATCH 3/5] objtool: Support Clang non-section symbols in ORC
 generation

On Wed, Apr 01, 2020 at 01:23:27PM -0500, Josh Poimboeuf wrote:

> @@ -105,8 +100,32 @@ static int create_orc_entry(struct elf *elf, struct section *u_sec, struct secti
>  	}
>  	memset(rela, 0, sizeof(*rela));
>  
> -	rela->sym = insn_sec->sym;
> -	rela->addend = insn_off;
> +	if (insn_sec->sym) {
> +		rela->sym = insn_sec->sym;
> +		rela->addend = insn_off;
> +	} else {
> +		/*
> +		 * The Clang assembler doesn't produce section symbols, so we
> +		 * have to reference the function symbol instead:
> +		 */
> +		rela->sym = find_symbol_containing(insn_sec, insn_off);

It's a good thing I made that a lot faster I suppose ;-)

> +		if (!rela->sym) {
> +			/*
> +			 * Hack alert.  This happens when we need to reference
> +			 * the NOP pad insn immediately after the function.
> +			 */
> +			rela->sym = find_symbol_containing(insn_sec,
> +							   insn_off - 1);

Urgh, when does that happen? 

> +		}
> +		if (!rela->sym) {
> +			WARN("missing symbol for insn at offset 0x%lx\n",
> +			     insn_off);
> +			return -1;
> +		}
> +
> +		rela->addend = insn_off - rela->sym->offset;
> +	}
> +
>  	rela->type = R_X86_64_PC32;
>  	rela->offset = idx * sizeof(int);
>  	rela->sec = ip_relasec;
> -- 
> 2.21.1
>