On Thu, Jul 10, 2008 at 03:50:29PM +0300, Sergei Trofimovich wrote:
> Small ARCH=um SUBARCH=i386 .config is in attach.
> How to fix properly such kind of miscompilation? (gcc-4.3.1)
> Now I have to use hacks like this:

Use the patch below instead.


Work email - jdike at linux dot intel dot com

commit 4f81c5350b44bcc501ab6f8a089b16d064b4d2f6
Author: Jeff Dike
Date: Mon Jul 7 13:36:56 2008 -0400

[UML] fix gcc ICEs and unresolved externs

There are various constraints on the use of unit-at-a-time:
- i386 uses no-unit-at-a-time for pre-4.0 (not 4.3)
- x86_64 uses unit-at-a-time always

Uli reported a crash on x86_64 with gcc 4.1.2 with unit-at-a-time,
resulting in commit c0a18111e571138747a98af18b3a2124df56a0d1

Ingo reported a gcc internal error with gcc 4.3 with no-unit-at-a-timem,
resulting in 22eecde2f9034764a3fd095eecfa3adfb8ec9a98

Benny Halevy is seeing extern inlines not resolved with gcc 4.3 with

This patch reintroduces unit-at-a-time for gcc >= 4.0, bringing back the
possibility of Uli's crash. If that happens, we'll debug it.

I started seeing both the internal compiler errors and unresolved
inlines on Fedora 9. This patch fixes both problems, without so far
reintroducing the crash reported by Uli.

Signed-off-by: Jeff Dike
Cc: Benny Halevy
Cc: Adrian Bunk
Cc: Ingo Molnar
Cc: Ulrich Drepper
Signed-off-by: Linus Torvalds

diff --git a/arch/um/Makefile b/arch/um/Makefile
index dbeab15..ca40397 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -77,7 +77,6 @@ include $(srctree)/$(ARCH_DIR)/Makefile-os-$(OS)
KERNEL_DEFINES = $(strip -Derrno=kernel_errno -Dsigprocmask=kernel_sigprocmask \
-Dmktime=kernel_mktime $(ARCH_KERNEL_DEFINES))
-KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time,)

PHONY += linux

diff --git a/arch/um/Makefile-i386 b/arch/um/Makefile-i386
index 561e373..302cbe5 100644
--- a/arch/um/Makefile-i386
+++ b/arch/um/Makefile-i386
@@ -32,4 +32,11 @@ cflags-y += $(call cc-option,-mpreferred-stack-boundary=2)
# an unresolved reference.
cflags-y += -ffreestanding

+# Disable unit-at-a-time mode on pre-gcc-4.0 compilers, it makes gcc use
+# a lot more stack due to the lack of sharing of stacklots. Also, gcc
+# 4.3.0 needs -funit-at-a-time for extern inline functions.
+KBUILD_CFLAGS += $(shell if [ $(call cc-version) -lt 0400 ] ; then \
+ echo $(call cc-option,-fno-unit-at-a-time); \
+ else echo $(call cc-option,-funit-at-a-time); fi
KBUILD_CFLAGS += $(cflags-y)
diff --git a/arch/um/Makefile-x86_64 b/arch/um/Makefile-x86_64
index 8ed362f..a9cd7e7 100644
--- a/arch/um/Makefile-x86_64
+++ b/arch/um/Makefile-x86_64
@@ -21,3 +21,6 @@ HEADER_ARCH := x86

LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib64
LINK-y += -m64
+# Do unit-at-a-time unconditionally on x86_64, following the host
+KBUILD_CFLAGS += $(call cc-option,-funit-at-a-time)
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