lkml.org 
[lkml]   [2017]   [Sep]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more clear and consistent
On Thu, Sep 14, 2017 at 01:45:29PM -0500, Josh Poimboeuf wrote:
> On Thu, Sep 14, 2017 at 11:28:30AM -0700, Linus Torvalds wrote:
> > On Thu, Sep 14, 2017 at 10:33 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > >>
> > >> a) uglifying the 15 or so relevant inline asm locations with ifdefs; or
> > >
> > > Actually I guess we could put the "sp" in a macro... I'll try it.
> >
> > Exactly. Do something like
> >
> > #ifdef CONFIG_FRAME_POINTER
> > # define EXTRA_ASM_CLOBBERS "rsp"
> > #else
> > # define EXTRA_ASM_CLOBBERS
> > #endif
> >
> > and then replace the nasty
> >
> > register void *__sp asm(_ASM_SP);
> > ..
> > "+r" (__sp)
> >
> > games with just that EXTRA_ASM_CLOBBERS thing at the end of the clobbers.
> >
> > Yes, you'd probably have to document that the alternative_call_2()
> > thing doesn't take a "input" argument, but a input_and_clobbers, but
> > all users do that anyway.
> >
> > I dunno.
>
> There's also alternative_call(), which doesn't yet have the '__rsp'
> annotation, but it probably should. It has some callers which pass
> clobbers and some which don't, so its conversion would be trickier.
>
> So my plan is to keep patch 3 of this series, which clarifies those
> alternative macro interfaces, and also separates the inputs from the
> clobbers. That'll make it really easy to add something like
> EXTRA_ASM_CLOBBERS above.
>
> In fact I'll probably keep patches 1-3, because they're all
> improvements. Then I'll replace the original patch 4 (ASM_CALL) with
> the "sp" clobbers thing.

So I couldn't figure out how to make it any simpler than this:

#ifdef CONFIG_FRAME_POINTER
# define ASM_CALL_CLOBBERS "sp"
# define ASM_CALL_CLOBBERS_APPEND , ASM_CALL_CLOBBERS
# define ASM_CALL_CLOBBERS_ARGS(args...) ASM_CALL_CLOBBERS, ## args
#else
# define ASM_CALL_CLOBBERS
# define ASM_CALL_CLOBBERS_APPEND
# define ASM_CALL_CLOBBERS_ARGS(args...) args
#endif


ASM_CALL_CLOBBERS is the normal one:

asm volatile("call foo" : : : ASM_CALL_CLOBBERS);


ASM_CALL_CLOBBERS_APPEND is needed when combining the option with other
clobbers options, like:

asm volatile("call foo" : : : "memory" ASM_CALL_CLOBBERS_APPEND);


ASM_CALL_CLOBBERS_ARGS is needed for the pesky alternative_call() macro
so it can work with the variadic argument:

#define alternative_call(oldfunc, newfunc, feature, outputs, inputs, \
clobbers...) \
asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", \
feature), \
: outputs \
: [old] "i" (oldfunc), [new] "i" (newfunc) \
ARGS_APPEND(inputs) \
: ASM_CALL_CLOBBERS_ARGS(clobbers))


So I *was* about ready to post something like the above. But, of
course, the kbuild robot found that the new version of my patches
manages to crash GCC with a certain randconfig.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82221

So the saga continues. Now I've managed to break clang, sparse, and GCC
with each consecutive iteration of these patches... I'm starting to
lose my faith in compilers.

--
Josh

\
 
 \ /
  Last update: 2017-09-15 18:11    [W:0.087 / U:0.676 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site