Kaz wrote:
> Hi All,
>
> Not really a kernel-related question. I've discovered that GCC 4.1.1
> (which I'm not using for kernel compiling, but user space) generates
> branch likely instructions by default, even though the documentation
> says that their use is off by default for MIPS32 and MIPS64, because
That's because the compiler is not configured correctly. The default CPU
string "from-abi" ends up being used, and so the target ISA is MIPS III.
> In parallel with writing some tests, I thought I would ask whether
> anyone happens know whether or not these instructions are known to
> actually work correctly on the SB1480 silicon (and perhaps any
> additional details, like what revisions, etc)?
A basic sanity test does find bnezl working.
#include <stdio.h>
#include <stdlib.h>
static int branch_likely_works(void)
{
int one = 1;
int result;
__asm__ __volatile__
(" .set push\n"
" .set noreorder\n"
"1: move %0, $0\n"
" bnezl %0, 1b\n"
" lw %0, %1\n"
" .set pop\n"
: "=r" (result)
: "m" (one));
return result == 0;
}
int main(void)
{
if (branch_likely_works()) {
puts("branch-likely instruction bnezl correctly annuls delay
slot");
return 0;
}
puts("branch-likely instruction bnezl fails to annul delay slot");
return EXIT_FAILURE;
}
