Messages in this thread | | | Date | Thu, 29 Nov 2018 14:27:39 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64 |
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On Thu, 29 Nov 2018 13:22:11 -0600 Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Thu, Nov 29, 2018 at 02:16:48PM -0500, Steven Rostedt wrote: > > > and honestly, the way "static_call()" works now, can you guarantee > > > that the call-site doesn't end up doing that, and calling the > > > trampoline function for two different static calls from one indirect > > > call? > > > > > > See what I'm talking about? Saying "callers are wrapped in macros" > > > doesn't actually protect you from the compiler doing things like that. > > > > > > In contrast, if the call was wrapped in an inline asm, we'd *know* the > > > compiler couldn't turn a "call wrapper(%rip)" into anything else. > > > > But then we need to implement all numbers of parameters. > > I actually have an old unfinished patch which (ab)used C macros to > detect the number of parameters and then setup the asm constraints > accordingly. At the time, the goal was to optimize the BUG code. > > I had wanted to avoid this kind of approach for static calls, because > "ugh", but now it's starting to look much more appealing. > > Behold: > > diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h > index aa6b2023d8f8..d63e9240da77 100644 > --- a/arch/x86/include/asm/bug.h > +++ b/arch/x86/include/asm/bug.h > @@ -32,10 +32,59 @@ > > #ifdef CONFIG_DEBUG_BUGVERBOSE > > -#define _BUG_FLAGS(ins, flags) \ > +#define __BUG_ARGS_0(ins, ...) \ > +({\ > + asm volatile("1:\t" ins "\n"); \ > +}) > +#define __BUG_ARGS_1(ins, ...) \ > +({\ > + asm volatile("1:\t" ins "\n" \ > + : : "D" (ARG1(__VA_ARGS__))); \ > +}) > +#define __BUG_ARGS_2(ins, ...) \ > +({\ > + asm volatile("1:\t" ins "\n" \ > + : : "D" (ARG1(__VA_ARGS__)), \ > + "S" (ARG2(__VA_ARGS__))); \ > +}) > +#define __BUG_ARGS_3(ins, ...) \ > +({\ > + asm volatile("1:\t" ins "\n" \ > + : : "D" (ARG1(__VA_ARGS__)), \ > + "S" (ARG2(__VA_ARGS__)), \ > + "d" (ARG3(__VA_ARGS__))); \ > +}) > +#define __BUG_ARGS_4(ins, ...) \ > +({\ > + asm volatile("1:\t" ins "\n" \ > + : : "D" (ARG1(__VA_ARGS__)), \ > + "S" (ARG2(__VA_ARGS__)), \ > + "d" (ARG3(__VA_ARGS__)), \ > + "c" (ARG4(__VA_ARGS__))); \ > +}) > +#define __BUG_ARGS_5(ins, ...) \ > +({\ > + register u64 __r8 asm("r8") = (u64)ARG5(__VA_ARGS__); \ > + asm volatile("1:\t" ins "\n" \ > + : : "D" (ARG1(__VA_ARGS__)), \ > + "S" (ARG2(__VA_ARGS__)), \ > + "d" (ARG3(__VA_ARGS__)), \ > + "c" (ARG4(__VA_ARGS__)), \ > + "r" (__r8)); \ > +}) > +#define __BUG_ARGS_6 foo > +#define __BUG_ARGS_7 foo > +#define __BUG_ARGS_8 foo > +#define __BUG_ARGS_9 foo > +
There exist tracepoints with 13 arguments.
-- Steve
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