unsigned long CTimer::GetTicks(void)
{
asm volatile //Taken from AMD SDK
(
"xor %eax, %eax;"
"xor %ebx, %ebx;"
"xor %ecx, %ecx;"
"xor %edx, %edx;"
"cpuid;"
"rdtsc;"
"mov %eax, (_g_Elapsed);"
: //no output registers
: //nothing here either
: "%eax", "%ebx", "%ecx", "%edx"
);
return g_Elapsed;
}
Trouble converting VC inline ASM to GCC inline ASM
Author
So I woke up 7 AM this morning after having spent a good part of the night trying to figure out why this returns an error when I try to compile it in DevC++ (using the GCC compiler). The code sample I took it from originally was for VC I believe, watching the syntax.
The problem is not the code part. The problem is the fourth part, that is the "clobbed" registers' entry. If I compile without the clobbed registers I don't get any erros (in fact the code works until it is run somewhere where the destruction of EAX, EBX, ECX and EDX doesn't matter). When I try to compile it like the code above I get:
"invalid `asm', C:\Dev\Rome\Code\Timer Win32.cpp:9, operand number missing after %-letter"
This same error repeats itself 9 times additionally. It makes no sense since I think the syntax which I use it quite correct. Thus I have to turn to the forums for help...
Author
Never mind, I just found out what caused the error (though I don't see why). Using the % prefix for the registers is fine until they are added to the clobbered registers' list. If they are, they must be prefixed with a double %%. Example:
unsigned long CTimer::GetTicks(void){ asm volatile //Taken from AMD SDK ( "xor %%eax, %%eax;" "xor %%ebx, %%ebx;" "xor %%ecx, %%ecx;" "xor %%edx, %%edx;" "cpuid;" "rdtsc;" "mov %%eax, (_g_Elapsed);" : //no output registers : //nothing here either : "%eax", "%ebx", "%ecx", "%edx" ); return g_Elapsed;}This topic is closed to new replies.
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