[PATCH bpf-next v2] bpftool: avoid sign extension in unsigned enum JSON dumps

[PATCH bpf-next v2] bpftool: avoid sign extension in unsigned enum JSON dumps

[Hungyu Lin]

The BTF enum value is stored in a signed 32-bit field even when the
enum is unsigned. Passing it directly to jsonw_uint_field(), which
takes a uint64_t, sign-extends values with bit 31 set. For example,
0xffffffffU is printed as 18446744073709551615 instead of 4294967295
by bpftool -j btf dump.

Cast the value to __u32 before widening it, matching the conversion
already used for plain-text output.

Fixes: c93cc69004df ("bpftool: add ability to dump BTF types")
Acked-by: Quentin Monnet <qmo@kernel.org>
Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
---
Changes in v2:
- Drop RFC as requested by Andrii.
- Add Quentin Monnet's Acked-by.
- No code changes.

v1 (RFC): https://patchwork.kernel.org/series/1196994/

 tools/bpf/bpftool/btf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index abd661db91e6..385521e6b028 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -482,7 +482,7 @@ static int dump_btf_type(const struct btf *btf, __u32 id,
 				if (btf_kflag(t))
 					jsonw_int_field(w, "val", v->val);
 				else
-					jsonw_uint_field(w, "val", v->val);
+					jsonw_uint_field(w, "val", (__u32)v->val);
 				jsonw_end_object(w);
 			} else {
 				if (btf_kflag(t))

base-commit: 7101b10cf281f629ac58c99697ca6f6d082b99a7
-- 
2.43.0

Re: [PATCH bpf-next v2] bpftool: avoid sign extension in unsigned enum JSON dumps

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Fri, 30 Oct 2026 19:53:43 +0000 you wrote:
> The BTF enum value is stored in a signed 32-bit field even when the
> enum is unsigned. Passing it directly to jsonw_uint_field(), which
> takes a uint64_t, sign-extends values with bit 31 set. For example,
> 0xffffffffU is printed as 18446744073709551615 instead of 4294967295
> by bpftool -j btf dump.
> 
> Cast the value to __u32 before widening it, matching the conversion
> already used for plain-text output.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v2] bpftool: avoid sign extension in unsigned enum JSON dumps
    https://git.kernel.org/bpf/bpf-next/c/eaae576c34d7

You are awesome, thank you!
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