Messages in this thread |  | | From | Michael Ellerman <> | Subject | Re: [PATCH v4 1/2] powerpc/uaccess: Implement unsafe_put_user() using 'asm goto' | Date | Wed, 06 May 2020 00:27:58 +1000 |
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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.
Plain "m" works, how much does the "<>" affect code gen in practice?
A quick diff here shows no difference from removing "<>".
cheers
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