From: Matthias Kaehlcke <mka@chromium.org>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>,
Arnd Bergmann <arnd@arndb.de>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
Nick Desaulniers <ndesaulniers@google.com>,
Stefan Agner <stefan@agner.ch>
Subject: Re: [PATCH v2] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
Date: Tue, 3 Sep 2019 11:48:16 -0700 [thread overview]
Message-ID: <20190903184816.GF70797@google.com> (raw)
In-Reply-To: <20190831060530.43082-1-natechancellor@gmail.com>
On Fri, Aug 30, 2019 at 11:05:31PM -0700, Nathan Chancellor wrote:
> Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build
> with clang:
>
> arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable':
> softirq.c:(.text+0x504): undefined reference to `mcount'
> arm-linux-gnueabi-ld: kernel/softirq.o: in function `__local_bh_enable_ip':
> softirq.c:(.text+0x58c): undefined reference to `mcount'
> arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq':
> softirq.c:(.text+0x6c8): undefined reference to `mcount'
> arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter':
> softirq.c:(.text+0x75c): undefined reference to `mcount'
> arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit':
> softirq.c:(.text+0x840): undefined reference to `mcount'
> arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more undefined references to `mcount' follow
>
> clang can emit a working mcount symbol, __gnu_mcount_nc, when
> '-meabi gnu' is passed to it. Until r369147 in LLVM, this was
> broken and caused the kernel not to boot with '-pg' because the
> calling convention was not correct. Always build with '-meabi gnu'
> when using clang but ensure that '-pg' (which is added with
> CONFIG_FUNCTION_TRACER and its prereq CONFIG_HAVE_FUNCTION_TRACER)
> cannot be added with it unless this is fixed (which means using
> clang 10.0.0 and newer).
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/35
> Link: https://bugs.llvm.org/show_bug.cgi?id=33845
> Link: https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Stefan Agner <stefan@agner.ch>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
prev parent reply other threads:[~2019-09-03 18:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-29 6:26 [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer Nathan Chancellor
2019-08-29 7:57 ` Stefan Agner
2019-08-29 16:20 ` Matthias Kaehlcke
2019-08-29 17:55 ` Nick Desaulniers
2019-08-29 19:34 ` Nathan Chancellor
2019-08-29 20:21 ` Stefan Agner
2019-08-29 20:57 ` Nick Desaulniers
2019-08-30 17:28 ` Nathan Chancellor
2019-08-30 21:13 ` Nick Desaulniers
2019-08-30 21:15 ` Nick Desaulniers
2019-08-31 6:05 ` [PATCH v2] " Nathan Chancellor
2019-09-03 18:48 ` Matthias Kaehlcke [this message]
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