On Fri, 2009-12-04 at 17:01 +0100, Louis Rilling wrote:
> On 04/12/09 7:29 -0800, Dave Hansen wrote:
> > This more closely resembles what glibc does.
> >
> > The last version had a push/popq %ebp. But, after looking at the glibc
> > code, I believe this to be unnecessary on 64-bit. Suka also pointed out
> > that we were neglecting to pull the subthread's function argument off
> > the stack.
> >
> > I also changed the register being used for the subthread variable to be
> > rax. This is just to more closely resemble the glibc code. It doesn't
> > hurt to use it this way mostly because we overwrite it for the exit
> > syscall anyway.
> >
> > int eclone(long flags_low, struct clone_args *clone_args, long args_size,
> > int *pids)
> > {
> > long retval;
> >
> > __asm__ __volatile__(
> > "movq %5, %%r10\n\t" /* pids in r10*/
> > "syscall\n\t" /* Linux/x86_64 system call */
> > "testq %0,%0\n\t" /* check return value */
> > "jne 1f\n\t" /* jump if parent */
> > "popq %%rax\n\t" /* get subthread function */
> > "popq %%rdi\n\t" /* get the subthread function arg */
> > "call *%%rax\n\t" /* start subthread function */
> > "movq %6,%0\n\t"
> > "syscall\n" /* exit system call: exit subthread */
> > "1:\n\t"
> > :"=a" (retval)
> > :"0" (__NR_clone3),/* eax */
> > "D" (flags_low), /* rdi */
> > "S" (clone_args), /* rsi */
> > "d" (args_size), /* rdx */
> > "m" (pids), /* gets moved to r10 */
> > "i" (__NR_exit)
> > :"rbx", "rcx", "r8", "r9", "r10"
>
> Why is rbx in the clobber list? It's not used at all.
Because I forgot to take it out when I removed the popq into rbx. :)
> r8 and r9 can be removed from the clobber list, since they can only be clobbered
> when calling the subthread, and then exit() is called without returning to C.
OK, that makes sense.
> syscall also destroys r11, so it should be added to the clobber list.
Even though it is a ptregscall?
> Libc also adds "cc" to the clobber list. I'm not sure that this matters though.
I guess it can't hurt. I'll add a comment about it.
-- Dave
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