[PATCH bpf-next] bpftool: Preserve unsigned enum64 values in data dumps

[PATCH bpf-next] bpftool: Preserve unsigned enum64 values in data dumps

[Hungyu Lin]

When an enum64 data value does not match a named enumerator,
btf_dumper_enum64() always prints it as signed. Unsigned values with
bit 63 set therefore appear negative in BTF-formatted map dump and
lookup output, in both plain and JSON modes. For example,
0x8000000000000001 is printed as -9223372036854775807 instead of
9223372036854775809.

Choose the numeric writer according to the enum's signedness. Keep
signed values and named enumerators unchanged.

Fixes: 58a53978fdf6 ("bpftool: Add btf enum64 support")
Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
---
 tools/bpf/bpftool/btf_dumper.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
index 3267163119dc..88c0da29f246 100644
--- a/tools/bpf/bpftool/btf_dumper.c
+++ b/tools/bpf/bpftool/btf_dumper.c
@@ -204,7 +204,10 @@ static int btf_dumper_enum64(const struct btf_dumper *d,
 		}
 	}
 
-	jsonw_int(d->jw, value);
+	if (btf_kflag(t))
+		jsonw_int(d->jw, value);
+	else
+		jsonw_uint(d->jw, value);
 	return 0;
 }
 

base-commit: eaae576c34d7e001767b6845a5950b0b8db3e68a
-- 
2.43.0

Re: [PATCH bpf-next] bpftool: Preserve unsigned enum64 values in data dumps

[Alexei Starovoitov]

On Sat, Oct 31, 2026 at 03:36 PM Hungyu Lin <dennylin0707@gmail.com> wrote:
> @@ -204,7 +204,10 @@ static int btf_dumper_enum64(const struct btf_dumper *d,
> -	jsonw_int(d->jw, value);
> +	if (btf_kflag(t))
> +		jsonw_int(d->jw, value);
> +	else
> +		jsonw_uint(d->jw, value);

btf_dumper_enum() has the same problem.

Fix all in one patch:

diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
index 3267163..09dd428 100644
--- a/tools/bpf/bpftool/btf_dumper.c
+++ b/tools/bpf/bpftool/btf_dumper.c
@@ -149,7 +149,8 @@ static int btf_dumper_enum(const struct btf_dumper *d,
 			    const void *data)
 {
 	const struct btf_enum *enums = btf_enum(t);
-	__s64 value;
+	bool is_signed = btf_kflag(t);
+	__s64 value, val;
 	__u32 i;

 	switch (t->size) {
@@ -157,20 +158,21 @@ static int btf_dumper_enum(const struct btf_dumper *d,
 		value = *(__s64 *)data;
 		break;
 	case 4:
-		value = *(__s32 *)data;
+		value = is_signed ? (__s64)*(__s32 *)data : *(__u32 *)data;
 		break;
 	case 2:
-		value = *(__s16 *)data;
+		value = is_signed ? *(__s16 *)data : *(__u16 *)data;
 		break;
 	case 1:
-		value = *(__s8 *)data;
+		value = is_signed ? *(__s8 *)data : *(__u8 *)data;
 		break;
 	default:
 		return -EINVAL;
 	}

 	for (i = 0; i < btf_vlen(t); i++) {
-		if (value == enums[i].val) {
+		val = is_signed ? (__s64)enums[i].val : (__u32)enums[i].val;
+		if (value == val) {
 			jsonw_string(d->jw,
 				     btf__name_by_offset(d->btf,
 							 enums[i].name_off));
@@ -178,7 +180,10 @@ static int btf_dumper_enum(const struct btf_dumper *d,
 		}
 	}

-	jsonw_int(d->jw, value);
+	if (is_signed)
+		jsonw_int(d->jw, value);
+	else
+		jsonw_uint(d->jw, value);
 	return 0;
 }

@@ -204,7 +209,10 @@ static int btf_dumper_enum64(const struct btf_dumper *d,
 		}
 	}

-	jsonw_int(d->jw, value);
+	if (btf_kflag(t))
+		jsonw_int(d->jw, value);
+	else
+		jsonw_uint(d->jw, value);
 	return 0;
 }


pw-bot: cr

Re: [PATCH bpf-next] bpftool: Preserve unsigned enum64 values in data dumps

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 1943 bytes --]

> bpftool: Preserve unsigned enum64 values in data dumps

TL;DR: Possible incomplete fix: as requested in the v1 review,
btf_dumper_enum() was left unchanged, so an unmatched unsigned 4-byte enum
value like 0xffffffff may still print as -1 in bpftool dumps.

> diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
> index 3267163119dc..88c0da29f246 100644
> --- a/tools/bpf/bpftool/btf_dumper.c
> +++ b/tools/bpf/bpftool/btf_dumper.c

[ ... ]

> @@ -204,7 +204,10 @@ static int btf_dumper_enum64(const struct btf_dumper *d,
>  		}
>  	}
>
> -	jsonw_int(d->jw, value);
> +	if (btf_kflag(t))
> +		jsonw_int(d->jw, value);
> +	else
> +		jsonw_uint(d->jw, value);
>  	return 0;
>  }
>

Alexei Starovoitov replied to v1 that btf_dumper_enum() has the same
problem and asked for both functions to be fixed in one patch, and he
supplied a diff for it.  I could not find a v2 on lore, and this patch still
only touches btf_dumper_enum64().

Was the request to cover btf_dumper_enum() intentionally left out?

btf_dumper_enum() still sign-extends the 1, 2 and 4 byte loads and always
prints an unmatched value with jsonw_int():

static int btf_dumper_enum(const struct btf_dumper *d,
			   const struct btf_type *t,
			   const void *data)
{
	...
	switch (t->size) {
	case 4:
		value = *(__s32 *)data;
		break;
	...
	}
	...
	jsonw_int(d->jw, value);
	return 0;
}

For example, an unsigned 4-byte enum holding 0xffffffff that matches no
enumerator would still be printed as -1.  Should btf_dumper_enum() pick the
zero- or sign-extending load based on btf_kflag(t), compare enumerators with
matching signedness, and call jsonw_uint() for unsigned enums, as in the
diff from the v1 review?


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/41249994972