Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

Josh Poimboeuf
2018-11-29T19:22:18Z

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