From: Kees Cook <keescook@chromium.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Guenter Roeck <linux@roeck-us.net>, Peter Rosin <peda@axentia.se>,
Andy Shevchenko <andy@kernel.org>,
Matteo Croce <mcroce@microsoft.com>,
Nathan Chancellor <nathan@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
llvm@lists.linux.dev, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] lib/test_string.c: Add test for strlen()
Date: Thu, 3 Feb 2022 12:45:36 -0800 [thread overview]
Message-ID: <202202031242.45A7F5704@keescook> (raw)
In-Reply-To: <CAKwvOdnJ3w2Jb9tBZ+JnEfviquj2WktemCd833f=_P66a0qVag@mail.gmail.com>
On Thu, Feb 03, 2022 at 11:50:34AM -0800, Nick Desaulniers wrote:
> The kernel does not link against a libc; but it does provide many
> symbols that libc would provide, with the same or similar enough
> semantics that I would strongly recommend we _don't_ use
> -ffreestanding in order to get such libcall optimizations (there are a
> lot; see https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
> for some examples) and simply use -fno-builtin-* when necessary, or
> fix the kernel implementations individually.
Right, we really don't want -ffreestanding. Rather, we want to not link
against libgcc. This is mostly true already, though some of the smaller
architectures still do:
$ git grep print-libgcc
arch/arc/Makefile:LIBGCC = $(shell $(CC) $(cflags-y) --print-libgcc-file-name)
arch/csky/Makefile: $(shell $(CC) $(KBUILD_CFLAGS) $(KCFLAGS) -print-libgcc-file-name)
arch/h8300/boot/compressed/Makefile:LIBGCC := $(shell $(CROSS-COMPILE)$(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name 2>/dev/null)
arch/nios2/Makefile:LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS) $(KCFLAGS) -print-libgcc-file-name)
arch/openrisc/Makefile:LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
arch/parisc/Makefile:LIBGCC := $(shell $(CC) -print-libgcc-file-name)
arch/xtensa/Makefile:LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
arch/xtensa/boot/boot-redboot/Makefile:LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
--
Kees Cook
prev parent reply other threads:[~2022-02-03 20:45 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-30 18:36 [PATCH] lib/test_string.c: Add test for strlen() Kees Cook
2022-01-30 18:56 ` Andy Shevchenko
2022-01-30 20:34 ` Kees Cook
2022-01-30 20:13 ` kernel test robot
2022-01-30 20:35 ` Kees Cook
2022-02-02 16:01 ` Guenter Roeck
2022-02-02 16:16 ` Andy Shevchenko
2022-02-02 20:52 ` Kees Cook
2022-02-02 23:12 ` Guenter Roeck
2022-02-03 8:04 ` Geert Uytterhoeven
2022-02-03 16:41 ` Kees Cook
2022-02-03 17:15 ` Kees Cook
2022-02-03 18:09 ` Geert Uytterhoeven
2022-02-03 19:50 ` Nick Desaulniers
2022-02-03 20:25 ` Kees Cook
2022-02-03 20:45 ` Kees Cook [this message]
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