Bernhard Rosenkraenzer wrote:
On Sunday, 12. November 2006 10:24, Avi Kivity wrote:
Or better yet, preprocessed source and full gcc command line (as seen on
'make V=1').
gcc -m32 -Wp,-MD,drivers/kvm/.kvm_main.o.d -nostdinc -isystem /usr/lib/gcc/i586-ark-linux/4.2.0/include -D__KERNEL__ -Iinclude -include
include/linux/autoconf.h -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -O2 -pipe -msoft-float -mpreferred-stack-boundary=2 -march=i686 -mtune=pentium3 -maccumulate-outgoing-args -DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1 -Iinclude/asm-i386/mach-default -fomit-frame-pointer -fno-stack-protector -Wdeclaration-after-statement -Wno-pointer-sign -DMODULE -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(kvm_main)" -D"KBUILD_MODNAME=KBUILD_STR(kvm)" -c -o
drivers/kvm/.tmp_kvm_main.o drivers/kvm/kvm_main.c
drivers/kvm/kvm_main.c: In function 'kvm_dev_ioctl_run':
drivers/kvm/kvm_main.c:153: error: 'asm' operand has impossible constraints
drivers/kvm/kvm_main.c:158: error: 'asm' operand has impossible constraints
It does look like a gcc bug -- -O0 makes it go away.
Details at http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29808
That's a different bug, gcc generates code that the assembler can't
handle. Might be an assembler bug.
It's the same thing, the code is taken from kvm_main.c:
static void load_fs(u16 sel)
{
asm ("mov %0, %%fs" : : "g"(sel)); <--- line 153
}
static void load_gs(u16 sel)
{
asm ("mov %0, %%gs" : : "g"(sel)); <--- line 158
}
'sel' is a variable, so gcc can't provide it as an immediate operand.
Specifying it as "rm" instead of "g" would have been better, but can't
have any real influence.
Can you compile it with -S and post the generated assembly?
It can't generate assembly with asm() constructs it perceives as invalid -- -S
produces the same error.
Well, for the code you posted in in the gcc bug, it probaby generated
something like
mov $0, %fs
which is indeed invalid assembly. But the kvm miscompile is something
else (running out of registers or something like that).
--
error compiling committee.c: too many arguments to function
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