Messages in this thread Patch in this message | | | Date | Thu, 29 Nov 2018 13:22:11 -0600 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64 |
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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 + +#define __BUG_ARGS(ins, num, ...) __BUG_ARGS_ ## num(ins, __VA_ARGS__) + +#define _BUG_ARGS(ins, num, ...) __BUG_ARGS(ins, num, __VA_ARGS__) + +#define _BUG_FLAGS(ins, flags, ...) \ do { \ - asm volatile("1:\t" ins "\n" \ - ".pushsection __bug_table,\"aw\"\n" \ + _BUG_ARGS(ins, NUM_ARGS(__VA_ARGS__), __VA_ARGS__); \ + asm volatile(".pushsection __bug_table,\"aw\"\n" \ "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \ "\t" __BUG_REL(%c0) "\t# bug_entry::file\n" \ "\t.word %c1" "\t# bug_entry::line\n" \ @@ -76,7 +125,7 @@ do { \ unreachable(); \ } while (0) -#define __WARN_FLAGS(flags) _BUG_FLAGS(ASM_UD0, BUGFLAG_WARNING|(flags)) +#define __WARN_FLAGS(flags, ...) _BUG_FLAGS(ASM_UD0, BUGFLAG_WARNING|(flags), __VA_ARGS__) #include <asm-generic/bug.h> diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h index 70c7732c9594..0cb16e912c02 100644 --- a/include/asm-generic/bug.h +++ b/include/asm-generic/bug.h @@ -58,8 +58,8 @@ struct bug_entry { #endif #ifdef __WARN_FLAGS -#define __WARN_TAINT(taint) __WARN_FLAGS(BUGFLAG_TAINT(taint)) -#define __WARN_ONCE_TAINT(taint) __WARN_FLAGS(BUGFLAG_ONCE|BUGFLAG_TAINT(taint)) +#define __WARN_TAINT(taint, args...) __WARN_FLAGS(BUGFLAG_TAINT(taint), args) +#define __WARN_ONCE_TAINT(taint, args...) __WARN_FLAGS(BUGFLAG_ONCE|BUGFLAG_TAINT(taint), args) #define WARN_ON_ONCE(condition) ({ \ int __ret_warn_on = !!(condition); \ @@ -84,11 +84,12 @@ void warn_slowpath_fmt_taint(const char *file, const int line, unsigned taint, extern void warn_slowpath_null(const char *file, const int line); #ifdef __WARN_TAINT #define __WARN() __WARN_TAINT(TAINT_WARN) +#define __WARN_printf(args...) __WARN_TAINT(TAINT_WARN, args) #else #define __WARN() warn_slowpath_null(__FILE__, __LINE__) +#define __WARN_printf(arg...) warn_slowpath_fmt(__FILE__, __LINE__, arg) #endif -#define __WARN_printf(arg...) warn_slowpath_fmt(__FILE__, __LINE__, arg) #define __WARN_printf_taint(taint, arg...) \ warn_slowpath_fmt_taint(__FILE__, __LINE__, taint, arg) /* used internally by panic.c */ diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 2d2721756abf..e641552e17cf 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -192,6 +192,14 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, # define unreachable() do { } while (1) #endif +#define __NUM_ARGS(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, N, ...) N +#define NUM_ARGS(...) __NUM_ARGS(0, ## __VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0) +#define ARG1(_1, ...) _1 +#define ARG2(_1, _2, ...) _2 +#define ARG3(_1, _2, _3, ...) _3 +#define ARG4(_1, _2, _3, _4, ...) _4 +#define ARG5(_1, _2, _3, _4, _5, ...) _5 + /* * KENTRY - kernel entry point * This can be used to annotate symbols (functions or data) that are used -- Josh
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