On Sun, Jun 29, 2008 at 10:32:43AM +0300, Benny Halevy wrote:
> Note that the crash happened with gcc 4.1.2 and it will get the
> -fno-unit-at-a-time flag with the proposed patch.
>
> That said, this option or the lack of it ought not to cause any
> runtime crashes. If it does, I'd feel much more comfortable to know
> exactly what the root cause is before deciding to use the flag to
> workaround^hide it.
I agree.
The constraints on [no-]unit-at-a-time that I see are:
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
Ingo reported a gcc internal error with gcc 4.3 with
no-unit-at-a-time
You are seeing extern inlines not resolved with gcc 4.3 with
no-unit-at-a-time
I'm tempted to follow x86 on this, with the results that
extern inlines should be fine
Ingo's gcc crash should not reappear
Uli's crash may reappear
If that crash does come back, I'd say we should just debug it. It's
likely UML implicitly relying on some gcc behavior anyway.
This is the patch that I'm dropping into my tree:
Index: linux-2.6.22/arch/um/Makefile-i386
===================================================================
--- linux-2.6.22.orig/arch/um/Makefile-i386 2008-05-29 11:21:25.000000000
-0400
+++ linux-2.6.22/arch/um/Makefile-i386 2008-06-30 12:20:01.000000000 -0400
@@ -32,4 +32,10 @@ cflags-y += $(call cc-option,-mpreferred
# 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 0403 ] ; then \
+ echo $(call cc-option,-fno-unit-at-a-time); fi ;)
+
KBUILD_CFLAGS += $(cflags-y)
Index: linux-2.6.22/arch/um/Makefile-x86_64
===================================================================
--- linux-2.6.22.orig/arch/um/Makefile-x86_64 2008-05-29 11:21:25.000000000
-0400
+++ linux-2.6.22/arch/um/Makefile-x86_64 2008-06-30 12:21:01.000000000
-0400
@@ -21,3 +21,6 @@ HEADER_ARCH := x86
LINK-$(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)
Jeff
--
Work email - jdike at linux dot intel dot com
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