[PATCH bpf-next] bpftool: fix a bug in subskeleton code generation

[Yonghong Song <yhs@fb.com>]

Compiled with clang by adding LLVM=1 both kernel and selftests/bpf
build, I hit the following compilation error:

In file included from /.../tools/testing/selftests/bpf/prog_tests/subskeleton.c:6:
  ./test_subskeleton_lib.subskel.h:168:6: error: variable 'err' is used uninitialized whenever
      'if' condition is true [-Werror,-Wsometimes-uninitialized]
          if (!s->progs)
              ^~~~~~~~~
  ./test_subskeleton_lib.subskel.h:181:11: note: uninitialized use occurs here
          errno = -err;
                   ^~~
  ./test_subskeleton_lib.subskel.h:168:2: note: remove the 'if' if its condition is always false
          if (!s->progs)
          ^~~~~~~~~~~~~~

The compilation error is triggered by the following code
        ...
        int err;

        obj = (struct test_subskeleton_lib *)calloc(1, sizeof(*obj));
        if (!obj) {
                errno = ENOMEM;
                goto err;
        }
        ...

  err:
        test_subskeleton_lib__destroy(obj);
        errno = -err;
        ...
in test_subskeleton_lib__open(). The 'err' is not initialized, yet it
is used in 'errno = -err' later.

The fix is to remove 'errno = -err' since errno has been set properly
in all incoming branches.

Cc: Delyan Kratunov <delyank@fb.com>
Fixes: 00389c58ffe9 ("00389c58ffe993782a8ba4bb5a34a102b1f6fe24")
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 tools/bpf/bpftool/gen.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 96bd2b33ccf6..7ba7ff55d2ea 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -1538,7 +1538,6 @@ static int do_subskeleton(int argc, char **argv)
 			return obj;					    \n\
 		err:							    \n\
 			%1$s__destroy(obj);				    \n\
-			errno = -err;					    \n\
 			return NULL;					    \n\
 		}							    \n\
 									    \n\
-- 
2.30.2