Messages in this thread | | | Date | Wed, 6 May 2020 19:58:52 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 14/18] static_call: Add static_cond_call() |
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On Wed, May 06, 2020 at 12:24:55PM -0500, Josh Poimboeuf wrote: > On Fri, May 01, 2020 at 10:29:03PM +0200, Peter Zijlstra wrote: > > +++ b/arch/x86/include/asm/static_call.h > > @@ -30,4 +30,14 @@ > > ".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \ > > ".popsection \n") > > > > +#define ARCH_DEFINE_STATIC_CALL_RETTRAMP(name) \ > > + asm(".pushsection .static_call.text, \"ax\" \n" \ > > + ".align 4 \n" \ > > + ".globl " STATIC_CALL_TRAMP_STR(name) " \n" \ > > + STATIC_CALL_TRAMP_STR(name) ": \n" \ > > + " ret; nop; nop; nop; nop; \n" \ > > + ".type " STATIC_CALL_TRAMP_STR(name) ", @function \n" \ > > + ".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \ > > + ".popsection \n") > > + > > The boilerplate in these two trampoline macros is identical except for > the actual instructions, maybe there could be a shared > __ARCH_DEFINE_STATIC_CALL_TRAMP(name, insns) macro which does most of > the dirty work.
I'm afraid that'll just make it less readable :/
> > #endif /* _ASM_STATIC_CALL_H */ > > --- a/arch/x86/kernel/static_call.c > > +++ b/arch/x86/kernel/static_call.c > > @@ -4,19 +4,41 @@ > > #include <linux/bug.h> > > #include <asm/text-patching.h> > > > > -static void __static_call_transform(void *insn, u8 opcode, void *func) > > +enum insn_type { > > + call = 0, /* site call */ > > + nop = 1, /* site cond-call */ > > + jmp = 2, /* tramp / site tail-call */ > > + ret = 3, /* tramp / site cond-tail-call */ > > +}; > > The lowercase enums threw me for a loop, I thought they were variables a > few times. Starting a new enum trend? :-)
I can UPPERCASE them I suppose, not sure where this came from.
> > void arch_static_call_transform(void *site, void *tramp, void *func) > > @@ -24,10 +46,10 @@ void arch_static_call_transform(void *si > > mutex_lock(&text_mutex); > > > > if (tramp) > > - __static_call_transform(tramp, JMP32_INSN_OPCODE, func); > > + __static_call_transform(tramp, jmp + !func, func); > > > > if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) > > - __static_call_transform(site, CALL_INSN_OPCODE, func); > > + __static_call_transform(site, !func, func); > > Clever enum math, but probably more robust to be ignorant of the values: > > if (tramp) > __static_call_transform(tramp, func ? jmp : ret, func); > > if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) > __static_call_transform(site, func ? call : nop, func); >
That is more readable, and I checked, GCC is clever enough to not actually emit branches for that, so w00t.
> > +++ b/include/linux/static_call.h > > @@ -16,7 +16,9 @@ > > * > > * DECLARE_STATIC_CALL(name, func); > > * DEFINE_STATIC_CALL(name, func); > > + * DEFINE_STATIC_COND_CALL(name, typename); > > * static_call(name)(args...); > > + * static_cond_call(name)(args...) > > * static_call_update(name, func); > > Missing semicolon, also an updated description/example would be useful.
Yes, I already promised Rasmus more documentation.
> On that note, what do you think about tweaking the naming from > > DEFINE_STATIC_COND_CALL(name, typename); > static_cond_call(name)(args...); > > to > > DEFINE_STATIC_CALL_NO_FUNC(name, typename); > static_call_if_func(name)(args...); > > ? > > Seems clearer to me. They're still STATIC_CALLs, so it seems logical to > keep those two words together. And NO_FUNC clarifies the initialized > value. > > Similarly RETTRAMP could be ARCH_DEFINE_STATIC_CALL_NO_FUNC.
What can I say, I'm sorta used to the old naming by now, but sure, any other opinions before I edit things?
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