Fwd: [tip:x86/x32] x32: Warn and disable rather than error if binutils too old

Fwd: [tip:x86/x32] x32: Warn and disable rather than error if binutils too old

[H. Peter Anvin]

Kbuild people - for the lack of a way to doing toolchain dependencies in
Kconfig I'm doing this right now for x32 support.  I am a little unclear
if this is the right thing to do, especially if I should be using := or
= here.

	-hpa

-------- Original Message --------
Subject: [tip:x86/x32] x32:  Warn and disable rather than error if
binutils too old
Date: Mon, 27 Feb 2012 14:21:55 -0800
From: tip-bot for H. Peter Anvin <hpa@linux.intel.com>
Reply-To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org,
       tglx@linutronix.de, hpa@linux.intel.com, mingo@elte.hu,
hjl.tools@gmail.com
To: linux-tip-commits@vger.kernel.org
CC: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com,
  tglx@linutronix.de, hpa@linux.intel.com, hjl.tools@gmail.com,
mingo@elte.hu

Commit-ID:  0bf6276392e990dd0da0ccd8e10f42597d503f29
Gitweb:
http://git.kernel.org/tip/0bf6276392e990dd0da0ccd8e10f42597d503f29
Author:     H. Peter Anvin <hpa@linux.intel.com>
AuthorDate: Mon, 27 Feb 2012 14:09:10 -0800
Committer:  H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Mon, 27 Feb 2012 14:09:10 -0800

x32: Warn and disable rather than error if binutils too old

If X32 is enabled in .config, but the binutils can't build it, issue a
warning and disable the feature rather than erroring out.

In order to support this, have CONFIG_X86_X32 be the option set in
Kconfig, and CONFIG_X86_X32_ABI be the option set by the Makefile when
it is enabled and binutils has been found to be functional.

Requested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: H. J. Lu <hjl.tools@gmail.com>
Link:
http://lkml.kernel.org/r/1329696488-16970-1-git-send-email-hpa@zytor.com
---
 arch/x86/Kconfig  |    4 ++--
 arch/x86/Makefile |   16 ++++++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c9d6c9e..e2b38b4 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2175,7 +2175,7 @@ config IA32_AOUT
 	---help---
 	  Support old a.out binaries in the 32bit emulation.

-config X86_X32_ABI
+config X86_X32
 	bool "x32 ABI for 64-bit mode (EXPERIMENTAL)"
 	depends on X86_64 && IA32_EMULATION && EXPERIMENTAL
 	---help---
@@ -2190,7 +2190,7 @@ config X86_X32_ABI

 config COMPAT
 	def_bool y
-	depends on IA32_EMULATION || X86_X32_ABI
+	depends on IA32_EMULATION || X86_X32

 config COMPAT_FOR_U64_ALIGNMENT
 	def_bool COMPAT
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 209ba12..31bb1eb 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -82,6 +82,22 @@ ifdef CONFIG_CC_STACKPROTECTOR
         endif
 endif

+ifdef CONFIG_X86_X32
+	x32_ld_ok := $(call try-run,\
+			/bin/echo -e '1: .quad 1b' | \
+			$(CC) $(KBUILD_AFLAGS) -c -xassembler -o "$$TMP" - && \
+			$(OBJCOPY) -O elf32-x86-64 "$$TMP" "$$TMPO" && \
+			$(LD) -m elf32_x86_64 "$$TMPO" -o "$$TMP",y,n)
+	ifeq ($(x32_ld_ok),y)
+		CONFIG_X86_X32_ABI := y
+		KBUILD_AFLAGS += -DCONFIG_X86_X32_ABI
+		KBUILD_CFLAGS += -DCONFIG_X86_X32_ABI
+	else
+		$(warning CONFIG_X86_X32 enabled but no binutils support)
+	endif
+endif
+export CONFIG_X86_X32_ABI
+
 # Don't unroll struct assignments with kmemcheck enabled
 ifeq ($(CONFIG_KMEMCHECK),y)
 	KBUILD_CFLAGS += $(call cc-option,-fno-builtin-memcpy)

Re: Fwd: [tip:x86/x32] x32: Warn and disable rather than error if binutils too old

[H. Peter Anvin]

On 02/27/2012 02:49 PM, H. Peter Anvin wrote:
> Kbuild people - for the lack of a way to doing toolchain dependencies in
> Kconfig I'm doing this right now for x32 support.  I am a little unclear
> if this is the right thing to do, especially if I should be using := or
> = here.
> 
> 	-hpa

Just to clarify: it seems to work as written.

	-hpa

Re: Fwd: [tip:x86/x32] x32: Warn and disable rather than error if binutils too old

[Sam Ravnborg]

On Mon, Feb 27, 2012 at 02:49:27PM -0800, H. Peter Anvin wrote:
> Kbuild people - for the lack of a way to doing toolchain dependencies in
> Kconfig I'm doing this right now for x32 support.  I am a little unclear
> if this is the right thing to do, especially if I should be using := or

Looks good at first look.

":=" is almost always the right choice if this is not part of a rule somewhere.
With ":=" the rhs is only evaluated once and the result stored in the
variable on the lhs.

In this particular case you only use the lhs once - so there is no
real difference.

Another important difference is that with ":=" the rhs is evaluated when
make see it first time.
With "=" make defer it until the lhs is used.

again in you case there is no difference as you use the lhs just after
you have the assignment.

[But I guess you already knew all this...]

	Sam