[PATCH bpf-next v2] bpf_encoder: Fix a verbose output issue

[Yonghong Song <yonghong.song@linux.dev>]

For the following test.c:
  $ cat test.c
  unsigned tar(int a);
  __attribute__((noinline)) static int foo(int a, int b)
  {
    return tar(a) + tar(a + 1);
  }
  __attribute__((noinline)) int bar(int a)
  {
    foo(a, 1);
    return 0;
  }
The llvm compilation:
  $ clang -O2 -g -c test.c
And then
  $ pahole -JV test.o
  btf_encoder__new: 'test.o' doesn't have '.data..percpu' sectio  n
  File test.o:
  [1] INT unsigned int size=4 nr_bits=32 encoding=(none)
  [2] INT int size=4 nr_bits=32 encoding=SIGNED
  search cu 'test.c' for percpu global variables.
  [3] FUNC_PROTO (anon) return=2 args=(2 a, [4] FUNC bar type_id=3
  [5] FUNC_PROTO (anon) return=2 args=(2 a, 2 b, [6] FUNC foo type_id=5

The above confused format is due to btf_encoder__add_func_proto_for_state().
The "is_last = param_idx == nr_params" is always false since param_idx
starts from 0. The below change fixed the issue:
  is_last = param_idx == (nr_params - 1)

With the fix, 'pahole -JV test.o' will produce the following:
  ...
  [3] FUNC_PROTO (anon) return=2 args=(2 a)
  [4] FUNC bar type_id=3
  [5] FUNC_PROTO (anon) return=2 args=(2 a, 2 b)
  [6] FUNC foo type_id=5
  ...

In addition, in btf_encoder__add_func_proto_for_ftype(), we have
  ++param_idx;
  if (ftype->unspec_parms) { ... }
This is correct but it is misleading since '++param_idx' is only needed
inside the above 'if' condition. So put '++param_idx' inside the
'if' condition to make code cleaner.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 btf_encoder.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index b37ee7f..ec6933e 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -865,10 +865,11 @@ static int32_t btf_encoder__add_func_proto_for_ftype(struct btf_encoder *encoder
 			return -1;
 	}
 
-	++param_idx;
-	if (ftype->unspec_parms)
+	if (ftype->unspec_parms) {
+		++param_idx;
 		if (btf_encoder__add_func_param(encoder, NULL, 0, param_idx == nr_params))
 			return -1;
+	}
 
 	return id;
 }
@@ -895,7 +896,7 @@ static int32_t btf_encoder__add_func_proto_for_state(struct btf_encoder *encoder
 	for (param_idx = 0; param_idx < nr_params; param_idx++) {
 		p = &state->parms[param_idx];
 		name = btf__name_by_offset(btf, p->name_off);
-		is_last = param_idx == nr_params;
+		is_last = param_idx == (nr_params - 1);
 
 		/* adding BTF data may result in a move of the
 		 * name string memory, so make a temporary copy.
-- 
2.47.3