On Thu, 8 Feb 2007 09:53:18 +0100, "Franck Bui-Huu" <vagabon.xyz@gmail.com>
wrote:
> I tried the following patch:
>
> diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
> index 229276a..046fb1b 100644
> --- a/arch/mips/kernel/signal.c
> +++ b/arch/mips/kernel/signal.c
> @@ -68,7 +68,9 @@ int setup_sigcontext(struct pt_regs *regs, struct
> sigcontext __user *sc)
> err |= __put_user(regs->cp0_epc, &sc->sc_pc);
>
> err |= __put_user(0, &sc->sc_regs[0]);
> - for (i = 1; i < 32; i++)
> + for (i = 1; i < 16; i++)
> + err |= __put_user(regs->regs[i], &sc->sc_regs[i]);
> + for (i = 24; i < 32; i++)
> err |= __put_user(regs->regs[i], &sc->sc_regs[i]);
>
> err |= __put_user(regs->hi, &sc->sc_mdhi);
> @@ -126,7 +128,9 @@ int restore_sigcontext(struct pt_regs *regs,
> struct sigcontext __user *sc)
> err |= __get_user(treg, &sc->sc_dsp); wrdsp(treg, DSP_MASK);
> }
>
> - for (i = 1; i < 32; i++)
> + for (i = 1; i < 16; i++)
> + err |= __get_user(regs->regs[i], &sc->sc_regs[i]);
> + for (i = 24; i < 32; i++)
> err |= __get_user(regs->regs[i], &sc->sc_regs[i]);
>
> err |= __get_user(used_math, &sc->sc_used_math);
>
> ...and it still passes LTP tests.
>
> Someone reported that not saving/restoring static registers may break
> user tools but the gain is important I think.
NO! This change might silently corrupt static registers!
If you did not restore static registers in kernel stack on
restore_sigcontext(), succeeding RESTORE_STATIC in restore_all will
load garbages to static registers.
Note that any hardware interrupts in middle of signal handler
overwrite pt_regs area in kernel stack.
I can still remember random static register corruption bug and how
hard to debug ...
---
Atsushi Nemoto
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