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From: Paul Burton <paul.burton@mips.com>
To: "linux-kbuild@vger.kernel.org" <linux-kbuild@vger.kernel.org>
Cc: "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Paul Burton <pburton@wavecomp.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: [PATCH] kbuild: Disable LD_DEAD_CODE_DATA_ELIMINATION with ftrace & GCC <= 4.7
Date: Wed, 9 Jan 2019 23:16:25 +0000	[thread overview]
Message-ID: <20190109231539.24613-1-paul.burton@mips.com> (raw)
In-Reply-To: <CAMuHMdUw9LMVb-8RSNVBEcDMVB9SFOdfF+kb20=gxJiWF1x8sQ@mail.gmail.com>

When building using GCC 4.7 or older, -ffunction-sections & the -pg flag
used by ftrace are incompatible. This causes warnings or build failures
(where -Werror applies) such as the following:

  arch/mips/generic/init.c:
    error: -ffunction-sections disabled; it makes profiling impossible

This used to be taken into account by the ordering of calls to cc-option
from within the top-level Makefile, which was introduced by commit
90ad4052e85c ("kbuild: avoid conflict between -ffunction-sections and
-pg on gcc-4.7"). Unfortunately this was broken when the
CONFIG_LD_DEAD_CODE_DATA_ELIMINATION cc-option check was moved to
Kconfig in commit e85d1d65cd8a ("kbuild: test dead code/data elimination
support in Kconfig"), because the flags used by this check no longer
include -pg.

Fix this by not allowing CONFIG_LD_DEAD_CODE_DATA_ELIMINATION to be
enabled at the same time as ftrace/CONFIG_FUNCTION_TRACER when building
using GCC 4.7 or older.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Fixes: e85d1d65cd8a ("kbuild: test dead code/data elimination support in Kconfig")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: stable@vger.kernel.org # v4.19+
---
 init/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/init/Kconfig b/init/Kconfig
index d47cb77a220e..c787f782148d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1124,6 +1124,7 @@ config LD_DEAD_CODE_DATA_ELIMINATION
 	bool "Dead code and data elimination (EXPERIMENTAL)"
 	depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
 	depends on EXPERT
+	depends on !FUNCTION_TRACER || !CC_IS_GCC || GCC_VERSION >= 40800
 	depends on $(cc-option,-ffunction-sections -fdata-sections)
 	depends on $(ld-option,--gc-sections)
 	help
-- 
2.20.1


       reply	other threads:[~2019-01-09 23:16 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CAMuHMdUw9LMVb-8RSNVBEcDMVB9SFOdfF+kb20=gxJiWF1x8sQ@mail.gmail.com>
2019-01-09 23:16 ` Paul Burton [this message]
2019-01-10  2:00   ` [PATCH] kbuild: Disable LD_DEAD_CODE_DATA_ELIMINATION with ftrace & GCC <= 4.7 Masahiro Yamada
2019-01-10 18:11     ` Paul Burton
2019-01-11  2:15       ` Masahiro Yamada
2019-01-11 19:06         ` [PATCH v2] " Paul Burton
2019-01-13  3:54           ` Masahiro Yamada

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