linux-hardening - Re: [PATCH] lib/test_string.c: Add test for strlen()

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Message-ID: <202202030911.4914709E@keescook>
Date:   Thu, 3 Feb 2022 09:15:51 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Guenter Roeck <linux@...ck-us.net>, Peter Rosin <peda@...ntia.se>,
        Andy Shevchenko <andy@...nel.org>,
        Matteo Croce <mcroce@...rosoft.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] lib/test_string.c: Add test for strlen()

On Thu, Feb 03, 2022 at 09:04:22AM +0100, Geert Uytterhoeven wrote:
> Not if -ffreestanding, which is what several architectures are
> using nowadays, to a.o. prevent gcc from replacing calls to stdlib
> functions to other stdlib functions (e.g. strncat() -> strlen() +
> store, strncmp() -> strcmp()), which breaks linking if the latter is
> only provided inline.

Hah, for i386:

arch/x86/Makefile
	# temporary until string.h is fixed
	KBUILD_CFLAGS += -ffreestanding

This "temporary" is from 2006. ;)

6edfba1b33c7 ("[PATCH] x86_64: Don't define string functions to builtin")

Removing that appears to solve it, and appears to build correctly. I'll
continue testing.

> It works after dropping -ffreestanding.

I wonder if the other architectures were just copying x86?

-- 
Kees Cook