[2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[Tetsuo Handa]

(Continued from http://lkml.org/lkml/2009/6/4/14 )
I tried to identify the location of gcc 3.3's internal error using
"make CONFIG_DEBUG_INFO=1 arch/x86/kvm/x86_emulate.s", and it turned out that
the location is emulate_2op_cl().

Commenting out like below solves the gcc's internal error.

diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
index ca91749..561b9b6 100644
--- a/arch/x86/kvm/x86_emulate.c
+++ b/arch/x86/kvm/x86_emulate.c
@@ -2070,7 +2070,7 @@ twobyte_insn:
                break;
        case 0xa4: /* shld imm8, r, r/m */
        case 0xa5: /* shld cl, r, r/m */
-               emulate_2op_cl("shld", c->src2, c->src, c->dst, ctxt->eflags);
+               //emulate_2op_cl("shld", c->src2, c->src, c->dst, ctxt->eflags);
                break;
        case 0xab:
              bts:              /* bts */
@@ -2080,7 +2080,7 @@ twobyte_insn:
                break;
        case 0xac: /* shrd imm8, r, r/m */
        case 0xad: /* shrd cl, r, r/m */
-               emulate_2op_cl("shrd", c->src2, c->src, c->dst, ctxt->eflags);
+               //emulate_2op_cl("shrd", c->src2, c->src, c->dst, ctxt->eflags);
                break;
        case 0xae:              /* clflush */
                break;

I think something is wrong with emulate_2op_cl() when compiled with gcc 3.3.5 .

Regards.

Re: [2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[Avi Kivity]

Tetsuo Handa wrote:
> (Continued from http://lkml.org/lkml/2009/6/4/14 )
> I tried to identify the location of gcc 3.3's internal error using
> "make CONFIG_DEBUG_INFO=1 arch/x86/kvm/x86_emulate.s", and it turned out that
> the location is emulate_2op_cl().
>
> Commenting out like below solves the gcc's internal error.
>
> diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
> index ca91749..561b9b6 100644
> --- a/arch/x86/kvm/x86_emulate.c
> +++ b/arch/x86/kvm/x86_emulate.c
> @@ -2070,7 +2070,7 @@ twobyte_insn:
>                 break;
>         case 0xa4: /* shld imm8, r, r/m */
>         case 0xa5: /* shld cl, r, r/m */
> -               emulate_2op_cl("shld", c->src2, c->src, c->dst, ctxt->eflags);
> +               //emulate_2op_cl("shld", c->src2, c->src, c->dst, ctxt->eflags);
>                 break;
>         case 0xab:
>               bts:              /* bts */
> @@ -2080,7 +2080,7 @@ twobyte_insn:
>                 break;
>         case 0xac: /* shrd imm8, r, r/m */
>         case 0xad: /* shrd cl, r, r/m */
> -               emulate_2op_cl("shrd", c->src2, c->src, c->dst, ctxt->eflags);
> +               //emulate_2op_cl("shrd", c->src2, c->src, c->dst, ctxt->eflags);
>                 break;
>         case 0xae:              /* clflush */
>                 break;
>
> I think something is wrong with emulate_2op_cl() when compiled with gcc 3.3.5 .
>
>   

This is on i386, not x86_64, yes?

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

Re: [2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[Tetsuo Handa]

Avi Kivity wrote:
> > I think something is wrong with emulate_2op_cl() when compiled with gcc 3.3.5 .
> 
> This is on i386, not x86_64, yes?
> 
Yes. Building "make allmodconfig" using Debian Sarge on i686 machine.

Re: [2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[Avi Kivity]

[-- Attachment #1: Type: text/plain, Size: 385 bytes --]

Tetsuo Handa wrote:
> Avi Kivity wrote:
>   
>>> I think something is wrong with emulate_2op_cl() when compiled with gcc 3.3.5 .
>>>       
>> This is on i386, not x86_64, yes?
>>
>>     
> Yes. Building "make allmodconfig" using Debian Sarge on i686 machine.
>   

Does the attached patch help?

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


[-- Attachment #2: fix-gcc3.3-register-pressure.patch --]
[-- Type: text/plain, Size: 509 bytes --]

diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
index 22c765d..01717a5 100644
--- a/arch/x86/kvm/x86_emulate.c
+++ b/arch/x86/kvm/x86_emulate.c
@@ -451,7 +451,7 @@ static u32 group2_table[] = {
 			_PRE_EFLAGS("0", "5", "2")				\
 			_op _suffix " %4,%1 \n"					\
 			_POST_EFLAGS("0", "5", "2")				\
-			: "=m" (_eflags), "+r" (_dstv), "=&r" (_tmp)		\
+			: "=m" (_eflags), "+rm" (_dstv), "=&r" (_tmp)		\
 			: "c" (_clv) , "r" (_srcv), "i" (EFLAGS_MASK)		\
 			); 							\
 										\

Re: [2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[Tetsuo Handa]

Avi Kivity wrote:
> Does the attached patch help?
Unfortunately, no.

# gcc -v
Reading specs from /usr/lib/gcc-lib/i486-linux/3.3.5/specs
Configured with: ../src/configure -v --enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-gxx-include-dir=/usr/include/c++/3.3 --enable-shared --enable-__cxa_atexit --with-system-zlib --enable-nls --without-included-gettext --enable-clocale=gnu --enable-debug --enable-java-gc=boehm --enable-java-awt=xlib --enable-objc-gc i486-linux
Thread model: posix
gcc version 3.3.5 (Debian 1:3.3.5-13)
# make arch/x86/kvm/x86_emulate.o
/usr/src/linux-2.6.30-rc8/arch/x86/Makefile:82: stack protector enabled but no compiler support
  CHK     include/linux/version.h
  CHK     include/linux/utsrelease.h
  SYMLINK include/asm -> include/asm-x86
  CALL    scripts/checksyscalls.sh
  CC [M]  arch/x86/kvm/x86_emulate.o
gcc: Internal error: Segmentation fault (program cc1)
Please submit a full bug report.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.
For Debian GNU/Linux specific bug reporting instructions,
see <URL:file:///usr/share/doc/gcc-3.3/README.Bugs>.

{standard input}: Assembler messages:
{standard input}:4331: Warning: end of file not at end of a line; newline inserted
make[1]: *** [arch/x86/kvm/x86_emulate.o] Error 1
make: *** [arch/x86/kvm/x86_emulate.o] Error 2

Re: [2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[Avi Kivity]

Tetsuo Handa wrote:
> Avi Kivity wrote:
>   
>> Does the attached patch help?
>>     
> Unfortunately, no.
>
>   

What if you change "rm" in the patch to "m"?

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

Re: [2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[Tetsuo Handa]

Avi Kivity wrote:
> What if you change "rm" in the patch to "m"?
It still fails.

        __asm__ __volatile__ (                      \
            _PRE_EFLAGS("0", "5", "2")              \
            _op _suffix " %4,%1 \n"                 \
            _POST_EFLAGS("0", "5", "2")             \
            : "=m" (_eflags), "+m" (_dstv), "=&r" (_tmp)        \
            : "c" (_clv) , "r" (_srcv), "i" (EFLAGS_MASK)       \
            );

Re: [2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[Avi Kivity]

Tetsuo Handa wrote:
> Avi Kivity wrote:
>   
>> What if you change "rm" in the patch to "m"?
>>     
> It still fails.
>
>         __asm__ __volatile__ (                      \
>             _PRE_EFLAGS("0", "5", "2")              \
>             _op _suffix " %4,%1 \n"                 \
>             _POST_EFLAGS("0", "5", "2")             \
>             : "=m" (_eflags), "+m" (_dstv), "=&r" (_tmp)        \
>             : "c" (_clv) , "r" (_srcv), "i" (EFLAGS_MASK)       \
>             );
>   

I can eliminate _tmp by using lahf/sahf, but it's not going to be a 
trivial patch.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

Re: [2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[Tetsuo Handa]

Avi Kivity wrote:
> I can eliminate _tmp by using lahf/sahf, but it's not going to be a 
> trivial patch.

I don't know what's happening here.

If I comment out (_dst).bytes == 2 , it compiles.
The problem happens only "w" + "unsigned short" case.

# diff -urp arch/x86/kvm/x86_emulate.c~ arch/x86/kvm/x86_emulate.c
--- arch/x86/kvm/x86_emulate.c~ 2009-06-03 12:07:25.000000000 +0900
+++ arch/x86/kvm/x86_emulate.c  2009-06-07 17:52:05.591542272 +0900
@@ -461,8 +461,8 @@ static u32 group2_table[] = {
        do {                                                                    \
                switch ((_dst).bytes) {                                         \
                case 2:                                                         \
-                       __emulate_2op_cl(_op, _cl, _src, _dst, _eflags,         \
-                                               "w", unsigned short);           \
+                       /* __emulate_2op_cl(_op, _cl, _src, _dst, _eflags,      \
+                          "w", unsigned short); */             \
                        break;                                                  \
                case 4:                                                         \
                        __emulate_2op_cl(_op, _cl, _src, _dst, _eflags,         \

Re: [2.6.30-rc8 KVM] gcc 3.3 dies at emulate_2op_cl().

[Avi Kivity]

Tetsuo Handa wrote:
> Avi Kivity wrote:
>   
>> I can eliminate _tmp by using lahf/sahf, but it's not going to be a 
>> trivial patch.
>>     
>
> I don't know what's happening here.
>
> If I comment out (_dst).bytes == 2 , it compiles.
> The problem happens only "w" + "unsigned short" case.
>
> # diff -urp arch/x86/kvm/x86_emulate.c~ arch/x86/kvm/x86_emulate.c
> --- arch/x86/kvm/x86_emulate.c~ 2009-06-03 12:07:25.000000000 +0900
> +++ arch/x86/kvm/x86_emulate.c  2009-06-07 17:52:05.591542272 +0900
> @@ -461,8 +461,8 @@ static u32 group2_table[] = {
>         do {                                                                    \
>                 switch ((_dst).bytes) {                                         \
>                 case 2:                                                         \
> -                       __emulate_2op_cl(_op, _cl, _src, _dst, _eflags,         \
> -                                               "w", unsigned short);           \
> +                       /* __emulate_2op_cl(_op, _cl, _src, _dst, _eflags,      \
> +                          "w", unsigned short); */             \
>                         break;                                                  \
>                 case 4:                                                         \
>                         __emulate_2op_cl(_op, _cl, _src, _dst, _eflags,         \
>   

It's a gcc register allocator bug.  Bugs don't have to be reasonable.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.