[uml-devel] Problem in compiling without optimisations

[uml-devel] Problem in compiling without optimisations

[Nikola Knezevic]

Hi all,
When I change Makefile to have -O0 instead of -O2, this is what I get
after make ARCH=um:

  CC      arch/um/kernel/skas/clone.o
arch/um/include/sysdep/stub.h: In function 'remap_stack':
arch/um/include/sysdep/stub.h:90: warning: asm operand 7 probably
doesn't match constraints
arch/um/include/sysdep/stub.h:90: error: impossible constraint in 'asm'
make[2]: *** [arch/um/kernel/skas/clone.o] Error 1
make[1]: *** [arch/um/kernel/skas] Error 2
make: *** [arch/um/kernel] Error 2

This is the culprit:
static inline void remap_stack(int fd, unsigned long offset)
{
        __asm__ volatile ("movl %%eax,%%ebp ; movl %0,%%eax ; int $0x80 ;"
                          "movl %7, %%ebx ; movl %%eax, (%%ebx)"
                          : : "g" (STUB_MMAP_NR), "b" (UML_CONFIG_STUB_DATA),
                            "c" (UM_KERN_PAGE_SIZE),
                            "d" (PROT_READ | PROT_WRITE),
                            "S" (MAP_FIXED | MAP_SHARED), "D" (fd),
                            "a" (offset),
                            "i" (&((struct stub_data *)
UML_CONFIG_STUB_DATA)->err)
                          : "memory");
}


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[uml-devel] Re: Problem in compiling without optimisations

[Nikola Knezevic]

On 5/22/06, Nikola Knezevic <laladelausanne@gmail.com> wrote:
> This is the culprit:
> static inline void remap_stack(int fd, unsigned long offset)
> {
>         __asm__ volatile ("movl %%eax,%%ebp ; movl %0,%%eax ; int $0x80 ;"
>                           "movl %7, %%ebx ; movl %%eax, (%%ebx)"
>                           : : "g" (STUB_MMAP_NR), "b" (UML_CONFIG_STUB_DATA),
>                             "c" (UM_KERN_PAGE_SIZE),
>                             "d" (PROT_READ | PROT_WRITE),
>                             "S" (MAP_FIXED | MAP_SHARED), "D" (fd),
>                             "a" (offset),
>                             "i" (&((struct stub_data *)
> UML_CONFIG_STUB_DATA)->err)
>                           : "memory");
> }

Well, after reading about asm constrains, solution was to change that
"i" to "g". Now, there are other problem, regarding inline functions
and their ordering. Related to kernel in whole: has anyone ever tried
to compile it without optimisations?

Cheers,
Nikola


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Re: [uml-devel] Problem in compiling without optimisations

[Jeff Dike]

On Mon, May 22, 2006 at 04:11:11PM +0200, Nikola Knezevic wrote:
> Hi all,
> When I change Makefile to have -O0 instead of -O2, this is what I get
> after make ARCH=um:

I don't think the kernel will build at all with -O0.

				Jeff


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Re: [uml-devel] Re: Problem in compiling without optimisations

[Jeff Dike]

On Mon, May 22, 2006 at 04:50:57PM +0200, Nikola Knezevic wrote:
> On 5/22/06, Nikola Knezevic <laladelausanne@gmail.com> wrote:
> >This is the culprit:
> >static inline void remap_stack(int fd, unsigned long offset)
> >{
> >        __asm__ volatile ("movl %%eax,%%ebp ; movl %0,%%eax ; int $0x80 ;"
> >                          "movl %7, %%ebx ; movl %%eax, (%%ebx)"
> >                          : : "g" (STUB_MMAP_NR), "b" 
> >                          (UML_CONFIG_STUB_DATA),
> >                            "c" (UM_KERN_PAGE_SIZE),
> >                            "d" (PROT_READ | PROT_WRITE),
> >                            "S" (MAP_FIXED | MAP_SHARED), "D" (fd),
> >                            "a" (offset),
> >                            "i" (&((struct stub_data *)
> >UML_CONFIG_STUB_DATA)->err)
> >                          : "memory");
> >}
> 
> Well, after reading about asm constrains, solution was to change that
> "i" to "g". 

Checking my fuzzy recollection of asm constraints -
	"i" means immediate, i.e. a compile-time constant and "g" means
anything?  So, "i" breaks when gcc isn't trying hard enough to turn that
expression into a constant.

If so, it doesn't look worth changing.

				Jeff


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Re: [uml-devel] Problem in compiling without optimisations

[Blaisorblade]

On Monday 22 May 2006 16:11, Nikola Knezevic wrote:
> Hi all,
> When I change Makefile to have -O0 instead of -O2, this is what I get
> after make ARCH=um:

There are other spots where -O0 would lead to failure; search for -O0 on the 
ML, I remember that adding -finline and something else made it work (IIRC 
2.6.15 time), and this code was present.

>   CC      arch/um/kernel/skas/clone.o
> arch/um/include/sysdep/stub.h: In function 'remap_stack':
> arch/um/include/sysdep/stub.h:90: warning: asm operand 7 probably
> doesn't match constraints
> arch/um/include/sysdep/stub.h:90: error: impossible constraint in 'asm'
> make[2]: *** [arch/um/kernel/skas/clone.o] Error 1
> make[1]: *** [arch/um/kernel/skas] Error 2
> make: *** [arch/um/kernel] Error 2
>
> This is the culprit:
> static inline void remap_stack(int fd, unsigned long offset)
> {
>         __asm__ volatile ("movl %%eax,%%ebp ; movl %0,%%eax ; int $0x80 ;"
>                           "movl %7, %%ebx ; movl %%eax, (%%ebx)"
>
>                           : : "g" (STUB_MMAP_NR), "b"
>                           : : (UML_CONFIG_STUB_DATA),
>
>                             "c" (UM_KERN_PAGE_SIZE),
>                             "d" (PROT_READ | PROT_WRITE),
>                             "S" (MAP_FIXED | MAP_SHARED), "D" (fd),
>                             "a" (offset),
>                             "i" (&((struct stub_data *)
> UML_CONFIG_STUB_DATA)->err)
>
>                           : "memory");
>
> }

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

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