On Mon, Aug 19, 2019 at 01:06:28PM +0000, Christophe Leroy wrote:
> __WARN() used to just call __WARN_TAINT(TAINT_WARN)
>
> But a call to printk() has been added in the commit identified below
> to print a "---- cut here ----" line.
>
> This change only applies to warnings using __WARN(), which means
> WARN_ON() where the condition is constant at compile time.
> For WARN_ON() with a non constant condition, the additional line is
> not printed.
>
> In addition, adding a call to printk() forces GCC to add a stack frame
> and save volatile registers. Powerpc has been using traps to implement
> warnings in order to avoid that.
>
> So, call __WARN_TAINT(TAINT_WARN) directly instead of using __WARN()
> in order to restore the previous behaviour.
>
> If one day powerpc wants the decorative "---- cut here ----" line, it
> has to be done in the trap handler, not in the WARN_ON() macro.
>
> Fixes: 6b15f678fb7d ("include/asm-generic/bug.h: fix "cut here" for WARN_ON
> for __WARN_TAINT architectures")
> Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
Ah! Hmpf. Yeah, that wasn't an intended side-effect of this fix.
It seems PPC is not alone in this situation of making this code much
noisier. It looks like there needs to be a way to indicate to the trap
handler that a message was delivered or not. Perhaps we can add another
taint flag?
-kees
> ---
> arch/powerpc/include/asm/bug.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index fed7e6241349..3928fdaebb71 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/arch/powerpc/include/asm/bug.h
> @@ -99,7 +99,7 @@
> int __ret_warn_on = !!(x); \
> if (__builtin_constant_p(__ret_warn_on)) { \
> if (__ret_warn_on) \
> - __WARN(); \
> + __WARN_TAINT(TAINT_WARN); \
> } else { \
> __asm__ __volatile__( \
> "1: "PPC_TLNEI" %4,0\n" \
> --
> 2.13.3
>
--
Kees Cook
