Messages in this thread |  | | Date | Tue, 5 May 2020 10:32:45 -0500 | From | Segher Boessenkool <> | Subject | Re: [PATCH v4 1/2] powerpc/uaccess: Implement unsafe_put_user() using 'asm goto' |
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Hi!
On Wed, May 06, 2020 at 12:27:58AM +1000, Michael Ellerman wrote: > Christophe Leroy <christophe.leroy@c-s.fr> writes: > > unsafe_put_user() is designed to take benefit of 'asm goto'. > > > > Instead of using the standard __put_user() approach and branch > > based on the returned error, use 'asm goto' and make the > > exception code branch directly to the error label. There is > > no code anymore in the fixup section. > > > > This change significantly simplifies functions using > > unsafe_put_user() > > > ... > > > > Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> > > --- > > arch/powerpc/include/asm/uaccess.h | 61 +++++++++++++++++++++++++----- > > 1 file changed, 52 insertions(+), 9 deletions(-) > > > > diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h > > index 9cc9c106ae2a..9365b59495a2 100644 > > --- a/arch/powerpc/include/asm/uaccess.h > > +++ b/arch/powerpc/include/asm/uaccess.h > > @@ -196,6 +193,52 @@ do { \ > > }) > > > > > > +#define __put_user_asm_goto(x, addr, label, op) \ > > + asm volatile goto( \ > > + "1: " op "%U1%X1 %0,%1 # put_user\n" \ > > + EX_TABLE(1b, %l2) \ > > + : \ > > + : "r" (x), "m<>" (*addr) \ > > The "m<>" here is breaking GCC 4.6.3, which we allegedly still support.
[ You shouldn't use 4.6.3, there has been 4.6.4 since a while. And 4.6 is nine years old now. Most projects do not support < 4.8 anymore, on any architecture. ]
> Plain "m" works, how much does the "<>" affect code gen in practice? > > A quick diff here shows no difference from removing "<>".
It will make it impossible to use update-form instructions here. That probably does not matter much at all, in this case.
If you remove the "<>" constraints, also remove the "%Un" output modifier?
Segher
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