[PATCH bpf-next] libbpf: Improve BPF_PROG2 macro code quality and description

[Yonghong Song <yhs@fb.com>]

Commit 34586d29f8df ("libbpf: Add new BPF_PROG2 macro") added BPF_PROG2
macro for trampoline based programs with struct arguments. Andrii
made a few suggestions to improve code quality and description.
This patch implemented these suggestions including better internal
macro name, consistent usage pattern for __builtin_choose_expr(),
simpler macro definition for always-inline func arguments and
better macro description.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
 tools/lib/bpf/bpf_tracing.h | 77 ++++++++++++++++++++++---------------
 1 file changed, 47 insertions(+), 30 deletions(-)

diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
index 8d4bdd18cb3d..a71ca48ea479 100644
--- a/tools/lib/bpf/bpf_tracing.h
+++ b/tools/lib/bpf/bpf_tracing.h
@@ -438,39 +438,45 @@ typeof(name(0)) name(unsigned long long *ctx)				    \
 static __always_inline typeof(name(0))					    \
 ____##name(unsigned long long *ctx, ##args)
 
-#ifndef ____bpf_nth
-#define ____bpf_nth(_, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, _20, _21, _22, _23, _24, N, ...) N
+#ifndef ___bpf_nth2
+#define ___bpf_nth2(_, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13,	\
+		    _14, _15, _16, _17, _18, _19, _20, _21, _22, _23, _24, N, ...) N
 #endif
-#ifndef ____bpf_narg
-#define ____bpf_narg(...) ____bpf_nth(_, ##__VA_ARGS__, 12, 12, 11, 11, 10, 10, 9, 9, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0)
+#ifndef ___bpf_narg2
+#define ___bpf_narg2(...)	\
+	___bpf_nth2(_, ##__VA_ARGS__, 12, 12, 11, 11, 10, 10, 9, 9, 8, 8, 7, 7,	\
+		    6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0)
 #endif
 
-#define BPF_REG_CNT(t) \
-	(__builtin_choose_expr(sizeof(t) == 1 || sizeof(t) == 2 || sizeof(t) == 4 || sizeof(t) == 8, 1,	\
-	 __builtin_choose_expr(sizeof(t) == 16, 2,							\
-			       (void)0)))
+#define ___bpf_reg_cnt(t) \
+	__builtin_choose_expr(sizeof(t) == 1, 1,	\
+	__builtin_choose_expr(sizeof(t) == 2, 1,	\
+	__builtin_choose_expr(sizeof(t) == 4, 1,	\
+	__builtin_choose_expr(sizeof(t) == 8, 1,	\
+	__builtin_choose_expr(sizeof(t) == 16, 2,	\
+			      (void)0)))))
 
 #define ____bpf_reg_cnt0()			(0)
-#define ____bpf_reg_cnt1(t, x)			(____bpf_reg_cnt0() + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt2(t, x, args...)		(____bpf_reg_cnt1(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt3(t, x, args...)		(____bpf_reg_cnt2(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt4(t, x, args...)		(____bpf_reg_cnt3(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt5(t, x, args...)		(____bpf_reg_cnt4(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt6(t, x, args...)		(____bpf_reg_cnt5(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt7(t, x, args...)		(____bpf_reg_cnt6(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt8(t, x, args...)		(____bpf_reg_cnt7(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt9(t, x, args...)		(____bpf_reg_cnt8(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt10(t, x, args...)	(____bpf_reg_cnt9(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt11(t, x, args...)	(____bpf_reg_cnt10(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt12(t, x, args...)	(____bpf_reg_cnt11(args) + BPF_REG_CNT(t))
-#define ____bpf_reg_cnt(args...)	 ___bpf_apply(____bpf_reg_cnt, ____bpf_narg(args))(args)
+#define ____bpf_reg_cnt1(t, x)			(____bpf_reg_cnt0() + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt2(t, x, args...)		(____bpf_reg_cnt1(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt3(t, x, args...)		(____bpf_reg_cnt2(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt4(t, x, args...)		(____bpf_reg_cnt3(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt5(t, x, args...)		(____bpf_reg_cnt4(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt6(t, x, args...)		(____bpf_reg_cnt5(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt7(t, x, args...)		(____bpf_reg_cnt6(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt8(t, x, args...)		(____bpf_reg_cnt7(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt9(t, x, args...)		(____bpf_reg_cnt8(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt10(t, x, args...)	(____bpf_reg_cnt9(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt11(t, x, args...)	(____bpf_reg_cnt10(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt12(t, x, args...)	(____bpf_reg_cnt11(args) + ___bpf_reg_cnt(t))
+#define ____bpf_reg_cnt(args...)	 ___bpf_apply(____bpf_reg_cnt, ___bpf_narg2(args))(args)
 
 #define ____bpf_union_arg(t, x, n) \
-	__builtin_choose_expr(sizeof(t) == 1, ({ union { struct { __u8 x; } ___z; t x; } ___tmp = { .___z = {ctx[n]}}; ___tmp.x; }), \
-	__builtin_choose_expr(sizeof(t) == 2, ({ union { struct { __u16 x; } ___z; t x; } ___tmp = { .___z = {ctx[n]} }; ___tmp.x; }), \
-	__builtin_choose_expr(sizeof(t) == 4, ({ union { struct { __u32 x; } ___z; t x; } ___tmp = { .___z = {ctx[n]} }; ___tmp.x; }), \
-	__builtin_choose_expr(sizeof(t) == 8, ({ union { struct { __u64 x; } ___z; t x; } ___tmp = {.___z = {ctx[n]} }; ___tmp.x; }), \
-	__builtin_choose_expr(sizeof(t) == 16, ({ union { struct { __u64 x, y; } ___z; t x; } ___tmp = {.___z = {ctx[n], ctx[n + 1]} }; ___tmp.x; }), \
+	__builtin_choose_expr(sizeof(t) == 1, ({ union { __u8 ___z[1]; t x; } ___tmp = { .___z = {ctx[n]}}; ___tmp.x; }), \
+	__builtin_choose_expr(sizeof(t) == 2, ({ union { __u16 ___z[1]; t x; } ___tmp = { .___z = {ctx[n]} }; ___tmp.x; }), \
+	__builtin_choose_expr(sizeof(t) == 4, ({ union { __u32 ___z[1]; t x; } ___tmp = { .___z = {ctx[n]} }; ___tmp.x; }), \
+	__builtin_choose_expr(sizeof(t) == 8, ({ union { __u64 ___z[1]; t x; } ___tmp = {.___z = {ctx[n]} }; ___tmp.x; }), \
+	__builtin_choose_expr(sizeof(t) == 16, ({ union { __u64 ___z[2]; t x; } ___tmp = {.___z = {ctx[n], ctx[n + 1]} }; ___tmp.x; }), \
 			      (void)0)))))
 
 #define ____bpf_ctx_arg0(n, args...)
@@ -486,7 +492,7 @@ ____##name(unsigned long long *ctx, ##args)
 #define ____bpf_ctx_arg10(n, t, x, args...)	, ____bpf_union_arg(t, x, n - ____bpf_reg_cnt10(t, x, args)) ____bpf_ctx_arg9(n, args)
 #define ____bpf_ctx_arg11(n, t, x, args...)	, ____bpf_union_arg(t, x, n - ____bpf_reg_cnt11(t, x, args)) ____bpf_ctx_arg10(n, args)
 #define ____bpf_ctx_arg12(n, t, x, args...)	, ____bpf_union_arg(t, x, n - ____bpf_reg_cnt12(t, x, args)) ____bpf_ctx_arg11(n, args)
-#define ____bpf_ctx_arg(n, args...)	___bpf_apply(____bpf_ctx_arg, ____bpf_narg(args))(n, args)
+#define ____bpf_ctx_arg(args...)	___bpf_apply(____bpf_ctx_arg, ___bpf_narg2(args))(____bpf_reg_cnt(args), args)
 
 #define ____bpf_ctx_decl0()
 #define ____bpf_ctx_decl1(t, x)			, t x
@@ -501,10 +507,21 @@ ____##name(unsigned long long *ctx, ##args)
 #define ____bpf_ctx_decl10(t, x, args...)	, t x ____bpf_ctx_decl9(args)
 #define ____bpf_ctx_decl11(t, x, args...)	, t x ____bpf_ctx_decl10(args)
 #define ____bpf_ctx_decl12(t, x, args...)	, t x ____bpf_ctx_decl11(args)
-#define ____bpf_ctx_decl(args...)	___bpf_apply(____bpf_ctx_decl, ____bpf_narg(args))(args)
+#define ____bpf_ctx_decl(args...)	___bpf_apply(____bpf_ctx_decl, ___bpf_narg2(args))(args)
 
 /*
- * BPF_PROG2 can handle struct arguments.
+ * BPF_PROG2 is an enhanced version of BPF_PROG in order to handle struct
+ * arguments. Since each struct argument might take one or two u64 values
+ * in the trampoline stack, argument type size is needed to place proper number
+ * of u64 values for each argument. Therefore, BPF_PROG2 has different
+ * syntax from BPF_PROG. For example, for the following BPF_PROG syntax,
+ *   int BPF_PROG(test2, int a, int b)
+ * the corresponding BPF_PROG2 synx is,
+ *   int BPF_PROG2(test2, int, a, int, b)
+ * where type and the corresponding argument name are separated by comma.
+ * If one or more argument is of struct type, BPF_PROG2 macro should be used,
+ *   int BPF_PROG2(test_struct_arg, struct bpf_testmod_struct_arg_1, a, int, b,
+ *		   int, c, int, d, struct bpf_testmod_struct_arg_2, e, int, ret)
  */
 #define BPF_PROG2(name, args...)						\
 name(unsigned long long *ctx);							\
@@ -512,7 +529,7 @@ static __always_inline typeof(name(0))						\
 ____##name(unsigned long long *ctx ____bpf_ctx_decl(args));			\
 typeof(name(0)) name(unsigned long long *ctx)					\
 {										\
-	return ____##name(ctx ____bpf_ctx_arg(____bpf_reg_cnt(args), args));	\
+	return ____##name(ctx ____bpf_ctx_arg(args));				\
 }										\
 static __always_inline typeof(name(0))						\
 ____##name(unsigned long long *ctx ____bpf_ctx_decl(args))
-- 
2.30.2