Re: [PATCH] PPC: fix stack alignment for signal handlers

[Paul Mackerras <paulus@samba.org>]

Roland McGrath writes:

> For PPC32 signal handlers, while the frame itself was of properly aligned
> size, no alignment of the starting stack pointer was done at all, so that a
> signal handler can still get a misaligned stack pointer if the interrupted
> registers had one, though the kernel isn't gratuitously misaligning good
> ones like it is for PPC64.  I added explicit alignment to fix that.

This part is unnecessary, because arch/ppc/kernel/signal.c:do_signal()
already aligns the stack pointer to a 16-byte boundary:

        if ((ka.sa.sa_flags & SA_ONSTACK) && current->sas_ss_size
            && !on_sig_stack(regs->gpr[1]))
                newsp = current->sas_ss_sp + current->sas_ss_size;
        else
                newsp = regs->gpr[1];
        newsp &= ~0xfUL;

        /* Whee!  Actually deliver the signal.  */
        if (ka.sa.sa_flags & SA_SIGINFO)
                handle_rt_signal(signr, &ka, &info, oldset, regs, newsp);
        else
                handle_signal(signr, &ka, &info, oldset, regs, newsp);

The additions to arch/ppc64/kernel/signal32.c are likewise
unnecessary, because do_signal32() also does newsp &= ~0xfUL (in fact
the code there is very similar to the ppc32 code).

You are correct about the 64-bit case though.  I thought we had fixed
that but evidently not.  Your patch looks fine as far as
arch/ppc64/kernel/signal.c is concerned.

Regards,
Paul.