[PATCH bpf] libbpf: silence uninitialized warning/error in btf_dump_dump_type_data

When compiling libbpf with gcc 4.8.5, we see:

  CC       staticobjs/btf_dump.o
btf_dump.c: In function ‘btf_dump_dump_type_data.isra.24’:
btf_dump.c:2296:5: error: ‘err’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  if (err < 0)
     ^
cc1: all warnings being treated as errors
make: *** [staticobjs/btf_dump.o] Error 1

While gcc 4.8.5 is too old to build the upstream kernel, it's possible it
could be used to build standalone libbpf which suffers from the same problem.
Silence the error by initializing 'err' to 0.  The warning/error seems to be
a false positive since err is set early in the function.  Regardless we
shouldn't prevent libbpf from building for this.

Fixes: 920d16af9b42 ("libbpf: BTF dumper support for typed data")

Signed-off-by: Alan Maguire <redacted>
---
 tools/lib/bpf/btf_dump.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 17db62b..5cae716 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c

@@ -2194,7 +2194,7 @@ static int btf_dump_dump_type_data(struct btf_dump *d,
 				   __u8 bits_offset,
 				   __u8 bit_sz)
 {
-	int size, err;
+	int size, err = 0;
 
 	size = btf_dump_type_data_check_overflow(d, t, id, data, bits_offset);
 	if (size < 0)

-- 
1.8.3.1

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko [off-list ref]:

On Mon, 29 Nov 2021 10:00:40 +0000 you wrote:

When compiling libbpf with gcc 4.8.5, we see:

  CC       staticobjs/btf_dump.o
btf_dump.c: In function ‘btf_dump_dump_type_data.isra.24’:
btf_dump.c:2296:5: error: ‘err’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  if (err < 0)
     ^
cc1: all warnings being treated as errors
make: *** [staticobjs/btf_dump.o] Error 1

[...]

Here is the summary with links:
  - [bpf] libbpf: silence uninitialized warning/error in btf_dump_dump_type_data
    https://git.kernel.org/bpf/bpf-next/c/43174f0d4597

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
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On Mon, Nov 29, 2021 at 2:01 AM Alan Maguire [off-list ref] wrote:

When compiling libbpf with gcc 4.8.5, we see:

  CC       staticobjs/btf_dump.o
btf_dump.c: In function ‘btf_dump_dump_type_data.isra.24’:
btf_dump.c:2296:5: error: ‘err’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  if (err < 0)
     ^
cc1: all warnings being treated as errors
make: *** [staticobjs/btf_dump.o] Error 1

While gcc 4.8.5 is too old to build the upstream kernel, it's possible it
could be used to build standalone libbpf which suffers from the same problem.
Silence the error by initializing 'err' to 0.  The warning/error seems to be
a false positive since err is set early in the function.  Regardless we
shouldn't prevent libbpf from building for this.

Fixes: 920d16af9b42 ("libbpf: BTF dumper support for typed data")

Signed-off-by: Alan Maguire <redacted>
---

Arnaldo also complained about this.

Applied to bpf-next, I don't think it needs to be in the bpf tree. Thanks.