GNAT Inline machine code

GNAT Inline machine code

[Magnus Andersson]

How do I read the system clock using GNAT inline assembler?

This results in compiler error "No code generated for file rdtsc.ads
(package spec)":

asm("rdtsc                            ");
asm("movl   %%eax, %0", Outputs => Interfaces.Unsigned_32'Asm_Output ("=g",
high123)  );

Thanks
/ Magnus

Re: GNAT Inline machine code

[Mark Johnson]

Magnus Andersson wrote:
> 
> How do I read the system clock using GNAT inline assembler?
> 
> This results in compiler error "No code generated for file rdtsc.ads
> (package spec)":
> 
> asm("rdtsc                            ");
> asm("movl   %%eax, %0", Outputs => Interfaces.Unsigned_32'Asm_Output ("=g",
> high123)  );
> 
Hmm. Not sure. We implement this as a function similar to...

  function Rdtsc return Interfaces.Unsigned_64 is
    Result : Interfaces.Unsigned_64;
  begin
  asm(" byte 0x0f, 0x31",
Interfaces.Unsigned_64'Asm_Output("=A",Result), Volatile=>True);
  return Result;
  end Rdtsc;

[I removed a bunch of our specific data types and code checks for this
example...]

to fetch the 64 bit value. Don't forget the Volatile flag for code like
this (for when you optimize). If you only want half the value, you could
modify this or use some more code to extract just what you want....
  --Mark