Marco Gerards wrote:
...
+static int
+addr_is_valid (grub_addr_t addr)
+{
+ volatile unsigned char * p = (volatile unsigned char *)addr;
Why volatile? I have the feeling it is not needed.
+ unsigned char x, y;
+ x = *p;
+ *p = x ^ 0xcf;
+ y = *p;
+ *p = x;
+ return y == (x ^ 0xcf);
+}
volatile is necessary here to tell the complier that the memory address
might not behave like regular memory. Otherwise, the optimizer might
legitimately remove memory accesses and then constant propagation
detects an unchanged value.
gcc actually does a very good job here. Result with volatile removed:
$ gcc -S -O -fomit-frame-pointer init.c && cat init.s
...
addr_is_valid:
movl $1, %eax
ret
...
aka:
static int
addr_is_valid (grub_addr_t addr)
{
return 1;
}
This is at least a proof that the original function returns the correct
result when real memory is present :-)
Christian
_______________________________________________
Grub-devel mailing list
Grub-devel@gnu.org
http://lists.gnu.org/mailman/listinfo/grub-devel
