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Subject[tip:x86/urgent] x86/build: convert function graph '-Os' error to warning
Commit-ID:  a5859c6d7b6114fc0e52be40f7b0f5451c4aba93
Gitweb: http://git.kernel.org/tip/a5859c6d7b6114fc0e52be40f7b0f5451c4aba93
Author: Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Tue, 18 Apr 2017 16:44:29 -0500
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 19 Apr 2017 09:57:23 +0200

x86/build: convert function graph '-Os' error to warning

For pre-4.6.0 versions of GCC, which don't have '-mfentry', the
'-maccumulate-outgoing-args' option is required for function graph
tracing in order to avoid GCC bug 42109.

However, GCC ignores '-maccumulate-outgoing-args' when '-Os' is
also set.

Currently we force a build error to prevent that scenario, but that
breaks randconfigs. So change the error to a warning which also
disables CONFIG_CC_OPTIMIZE_FOR_SIZE.

Reported-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kbuild test robot <fengguang.wu@intel.com>
Cc: kbuild-all@01.org
Link: http://lkml.kernel.org/r/20170418214429.o7fbwbmf4nqosezy@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/Makefile | 8 ++++++++
arch/x86/kernel/ftrace.c | 6 ------
2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index a94a4d1..49d160b 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -154,6 +154,14 @@ ifdef CONFIG_FUNCTION_GRAPH_TRACER
else
ifeq ($(call cc-option-yn, -mfentry), n)
ACCUMULATE_OUTGOING_ARGS := 1
+
+ # GCC ignores '-maccumulate-outgoing-args' when used with '-Os'.
+ # If '-Os' is enabled, disable it and print a warning.
+ ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
+ undefine CONFIG_CC_OPTIMIZE_FOR_SIZE
+ $(warning Disabling CONFIG_CC_OPTIMIZE_FOR_SIZE. Your compiler does not have -mfentry so you cannot optimize for size with CONFIG_FUNCTION_GRAPH_TRACER.)
+ endif
+
endif
endif
endif
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 0e5ceac..5b71535 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -29,12 +29,6 @@
#include <asm/ftrace.h>
#include <asm/nops.h>

-#if defined(CONFIG_FUNCTION_GRAPH_TRACER) && \
- !defined(CC_USING_FENTRY) && \
- !defined(CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE)
-# error The following combination is not supported: ((compiler missing -mfentry) || (CONFIG_X86_32 and !CONFIG_DYNAMIC_FTRACE)) && CONFIG_FUNCTION_GRAPH_TRACER && CONFIG_CC_OPTIMIZE_FOR_SIZE
-#endif
-
#ifdef CONFIG_DYNAMIC_FTRACE

int ftrace_arch_code_modify_prepare(void)
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