gcc optimization

[mcheung63]

void setGDTR(char *gdt, unsigned short numberOfGDTDescriptor) {
char gdtr[6];
memset(gdtr, 0, 6);
if (numberOfGDTDescriptor < 8192) {
if (numberOfGDTDescriptor == 0) {
*(unsigned short *)gdtr = (unsigned short) 0; //gdtr's limit is 8N-1
} else {
*(unsigned short *)gdtr = (unsigned short) (8 * numberOfGDTDescriptor)
- 1; //gdtr's limit is 8N-1
}
*(unsigned int *) (gdtr + 2) = gdt;
__asm__ __volatile__("lgdt (%%eax)"::"a"(gdtr));
}
}

GCC thinks I haven't used the gdtr variable, so all the line with gdtr will be be compiled into instruction code. May I know how to fix it?

thanks
from Peter ([email protected])

[frank]

Maybe try

Code: Select all

-O0

[01000101]

this may give GCC the hint:

Code: Select all

*(volatile unsigned short *)gdtr =

[gravaera]

Yup. 01000101 beat me to it. Whenever GCC engages in folly, I just volatile that ho (Ohhhh).

[mcheung63]

thanks gentlemen