Re: [Qemu-devel] [PATCH] kvm-unittest: fix build with gcc 4.3.X and older

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Oct 17, 2013 at 12:53:30PM +0200, Paolo Bonzini wrote:
> Il 16/10/2013 21:46, Michael S. Tsirkin ha scritto:
> > Old GCC didn't let you reference variable by
> > number if it is listed with a specific register
> > constraint, on the assumption you can just
> > use the register name explicitly.
> 
> Tell us the truth, you made this up. :)  Who doesn't do that for invalid
> asm error messages...

I guessed at the reason, yes.

> > Build fails with errors like this:
> > a.c:6: error: invalid 'asm': invalid operand code 'd'
> > 
> > To fix, let's just use %eax %al etc.
> 
> The problem is that %d0 is wrong.  The "d" modifier is for "print
> duplicated register operand for AVX instruction" (whatever that means)
> according to GCC source code (gcc/config/i386/i386.md).
> 
> You need to use %k0 according to the same file.

Aha!

> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  lib/x86/pci.c | 4 ++--
> >  x86/s3.c      | 4 ++--
> >  x86/vmexit.c  | 2 +-
> >  3 files changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/lib/x86/pci.c b/lib/x86/pci.c
> > index f95cd88..08f7ebf 100644
> > --- a/lib/x86/pci.c
> > +++ b/lib/x86/pci.c
> > @@ -3,13 +3,13 @@
> >  
> >  static void outl(unsigned short port, unsigned val)
> >  {
> > -    asm volatile("outl %d0, %w1" : : "a"(val), "Nd"(port));
> > +    asm volatile("outl %%eax, %w1" : : "a"(val), "Nd"(port));
> >  }
> >  
> >  static unsigned inl(unsigned short port)
> >  {
> >      unsigned data;
> > -    asm volatile("inl %w1, %d0" : "=a"(data) : "Nd"(port));
> > +    asm volatile("inl %w1, %%eax" : "=a"(data) : "Nd"(port));
> >      return data;
> >  }
> >  static uint32_t pci_config_read(pcidevaddr_t dev, uint8_t reg)
> > diff --git a/x86/s3.c b/x86/s3.c
> > index 1feb452..eeffa17 100644
> > --- a/x86/s3.c
> > +++ b/x86/s3.c
> > @@ -149,8 +149,8 @@ static inline int rtc_in(u8 reg)
> >  
> >  static inline void rtc_out(u8 reg, u8 val)
> >  {
> > -    asm volatile("outb %b1, $0x70; mov %b2, %b1; outb %b1, $0x71"
> > -		 : "+a"(reg) : "0"(reg), "ri"(val));
> > +    asm volatile("outb %%al, $0x70; mov %b1, %%al; outb %%al, $0x71"
> > +		 : "+a"(reg) : "ri"(val));
> 
> Are you sure about this?  The error message here is definitely not
> "invalid operand code 'b'".

This produced a different error about conflict in constrains I think,
Gleb saw it too.

> That said, the patch is correct.  It's only the commit message that is
> wrong.
> 
> I'm not sure about Gleb's patch.  I'll reply to his message.
> 
> Paolo
> 
> >  }
> >  
> >  extern char resume_start, resume_end;
> > diff --git a/x86/vmexit.c b/x86/vmexit.c
> > index 3b945de..29bc582 100644
> > --- a/x86/vmexit.c
> > +++ b/x86/vmexit.c
> > @@ -26,7 +26,7 @@ static void outw(unsigned short port, unsigned val)
> >  
> >  static void outl(unsigned short port, unsigned val)
> >  {
> > -    asm volatile("outl %d0, %w1" : : "a"(val), "Nd"(port));
> > +    asm volatile("outl %%eax, %w1" : : "a"(val), "Nd"(port));
> >  }
> >  
> >  static unsigned int inb(unsigned short port)
> >