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Date:   Mon, 12 Feb 2018 09:26:35 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Kees Cook <keescook@chromium.org>,
        Ulf Magnusson <ulfalizer@gmail.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        "Luis R . Rodriguez" <mcgrof@suse.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Sam Ravnborg <sam@ravnborg.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Pavel Machek <pavel@ucw.cz>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Jiri Kosina <jkosina@suse.cz>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Tejun Heo <tj@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC PATCH 4/7] kconfig: support new special property shell=
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On Sun, Feb 11, 2018 at 10:13:44AM -0800, Linus Torvalds wrote:

> That actually sounds like we could just
> 
>  (a) make gcc 4.5 be the minimum required version
> 
>  (b) actually error out if we find a bad compiler

So the unofficial plan was to enforce asm-goto and -fentry support by
hard failure to build, which would get us at gcc-4.6 and then remove all
the fallback cruft needed for those features -- for x86. If we want to
do this tree wide, that's obviously OK with me too ;-)

The below is the two force-asm-goto and force-fentry patches folded.

---
 Makefile          | 17 +++++++++++------
 arch/x86/Makefile | 25 +++++--------------------
 2 files changed, 16 insertions(+), 26 deletions(-)

diff --git a/Makefile b/Makefile
index d192dd826cce..1a46f23d0974 100644
--- a/Makefile
+++ b/Makefile
@@ -489,6 +489,17 @@ KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC)
 KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC)
 endif
 
+# check for 'asm goto'
+ifeq ($(shell $(srctree)/scripts/gcc-goto.sh $(CC) $(KBUILD_CFLAGS)), y)
+  CC_HAVE_ASM_GOTO := 1
+  KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
+  KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
+endif
+
+ifeq ($(call cc-option-yn, -mfentry), y)
+  CC_HAVE_FENTRY := 1
+endif
+
 ifeq ($(config-targets),1)
 # ===========================================================================
 # *config targets only - make sure prerequisites are updated, and descend
@@ -654,12 +665,6 @@ KBUILD_CFLAGS += $(call cc-ifversion, -lt, 0409, \
 # Tell gcc to never replace conditional load with a non-conditional one
 KBUILD_CFLAGS	+= $(call cc-option,--param=allow-store-data-races=0)
 
-# check for 'asm goto'
-ifeq ($(call shell-cached,$(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC) $(KBUILD_CFLAGS)), y)
-	KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
-	KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
-endif
-
 include scripts/Makefile.kcov
 include scripts/Makefile.gcc-plugins
 
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index fad55160dcb9..35cea458a7be 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -158,27 +158,12 @@ ifdef CONFIG_X86_X32
 endif
 export CONFIG_X86_X32_ABI
 
-#
-# If the function graph tracer is used with mcount instead of fentry,
-# '-maccumulate-outgoing-args' is needed to prevent a GCC bug
-# (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42109)
-#
-ifdef CONFIG_FUNCTION_GRAPH_TRACER
-  ifndef CONFIG_HAVE_FENTRY
-	ACCUMULATE_OUTGOING_ARGS := 1
-  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
+ifndef CC_HAVE_ASM_GOTO
+  $(error Compiler lacks asm-goto support.)
+endif
 
-    endif
-  endif
+ifndef CC_HAVE_FENTRY
+  $(error Compiler lacks -mfentry support.)
 endif
 
 #