Messages in this thread | | | Subject | Re: [PATCH v4 1/2] powerpc/uaccess: Implement unsafe_put_user() using 'asm goto' | From | Christophe Leroy <> | Date | Wed, 6 May 2020 20:10:57 +0200 |
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Le 06/05/2020 à 19:58, Segher Boessenkool a écrit : > On Wed, May 06, 2020 at 10:58:55AM +1000, Michael Ellerman wrote: >>>> 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. ] >> >> Moving up to 4.6.4 wouldn't actually help with this though would it? > > Nope. But 4.6.4 is a bug-fix release, 91 bugs fixed since 4.6.3, so you > should switch to it if you can :-) > >> Also I have 4.6.3 compilers already built, I don't really have time to >> rebuild them for 4.6.4. >> >> The kernel has a top-level minimum version, which I'm not in charge of, see: >> >> https://www.kernel.org/doc/html/latest/process/changes.html?highlight=gcc > > Yes, I know. And it is much preferred not to have stricter requirements > for Power, I know that too. Something has to give though :-/ > >> There were discussions about making 4.8 the minimum, but I'm not sure >> where they got to. > > Yeah, just petered out I think? > > All significant distros come with a 4.8 as system compiler. > >>>> 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? >> >> So like this? >> >> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h >> index 62cc8d7640ec..ca847aed8e45 100644 >> --- a/arch/powerpc/include/asm/uaccess.h >> +++ b/arch/powerpc/include/asm/uaccess.h >> @@ -207,10 +207,10 @@ do { \ >> >> #define __put_user_asm_goto(x, addr, label, op) \ >> asm volatile goto( \ >> - "1: " op "%U1%X1 %0,%1 # put_user\n" \ >> + "1: " op "%X1 %0,%1 # put_user\n" \ >> EX_TABLE(1b, %l2) \ >> : \ >> - : "r" (x), "m<>" (*addr) \ >> + : "r" (x), "m" (*addr) \ >> : \ >> : label) > > Like that. But you will have to do that to *all* places we use the "<>" > constraints, or wait for more stuff to fail? And, there probably are > places we *do* want update form insns used (they do help in some loops, > for example)? >
AFAICT, git grep "m<>" provides no result.
However many places have %Ux:
arch/powerpc/boot/io.h: __asm__ __volatile__("lbz%U1%X1 %0,%1; twi 0,%0,0; isync" arch/powerpc/boot/io.h: __asm__ __volatile__("stb%U0%X0 %1,%0; sync" arch/powerpc/boot/io.h: __asm__ __volatile__("lhz%U1%X1 %0,%1; twi 0,%0,0; isync" arch/powerpc/boot/io.h: __asm__ __volatile__("sth%U0%X0 %1,%0; sync" arch/powerpc/boot/io.h: __asm__ __volatile__("lwz%U1%X1 %0,%1; twi 0,%0,0; isync" arch/powerpc/boot/io.h: __asm__ __volatile__("stw%U0%X0 %1,%0; sync" arch/powerpc/include/asm/atomic.h: __asm__ __volatile__("lwz%U1%X1 %0,%1" : "=r"(t) : "m"(v->counter)); arch/powerpc/include/asm/atomic.h: __asm__ __volatile__("stw%U0%X0 %1,%0" : "=m"(v->counter) : "r"(i)); arch/powerpc/include/asm/atomic.h: __asm__ __volatile__("ld%U1%X1 %0,%1" : "=r"(t) : "m"(v->counter)); arch/powerpc/include/asm/atomic.h: __asm__ __volatile__("std%U0%X0 %1,%0" : "=m"(v->counter) : "r"(i)); arch/powerpc/include/asm/book3s/32/pgtable.h: stw%U0%X0 %2,%0\n\ arch/powerpc/include/asm/book3s/32/pgtable.h: stw%U0%X0 %L2,%1" arch/powerpc/include/asm/io.h: __asm__ __volatile__("sync;"#insn"%U1%X1 %0,%1;twi 0,%0,0;isync"\ arch/powerpc/include/asm/io.h: __asm__ __volatile__("sync;"#insn"%U0%X0 %1,%0" \ arch/powerpc/include/asm/nohash/pgtable.h: stw%U0%X0 %2,%0\n\ arch/powerpc/include/asm/nohash/pgtable.h: stw%U0%X0 %L2,%1" arch/powerpc/kvm/powerpc.c: asm ("lfs%U1%X1 0,%1; stfd%U0%X0 0,%0" : "=m" (fprd) : "m" (fprs) arch/powerpc/kvm/powerpc.c: asm ("lfd%U1%X1 0,%1; stfs%U0%X0 0,%0" : "=m" (fprs) : "m" (fprd)
Christophe
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