[PATCH bpf-next v2] libbpf: Add gating for arena globals relocation feature

[PATCH bpf-next v2] libbpf: Add gating for arena globals relocation feature

[Emil Tsalapatis]

Add feature gating for the arena globals relocation introduced in
commit c1f61171d44b. The commit depends on a previous commit in the
same patchset that is absent from older kernels (12a1fe6e12db,
"bpf/verifier: Do not limit maximum direct offset into arena map").
Without this commit, arena globals relocation with arenas >= 512MiB
fails to load and breaks libbpf's backwards compatibility.

Introduce a libbpf feature to check whether the running kernel includes
patch 12a1fe6e12db, and only relocate arena globals if it does.

CHANGELOG
---------

v1 -> v2 (https://lore.kernel.org/bpf/20260209210240.2051209-1-emil@etsalapatis.com/)

- Reworked test to use simpler array-based program (Andrii)

Fixes: c1f61171d44b ("libbpf: Move arena globals to the end of the arena")
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
---
 tools/lib/bpf/features.c        | 92 +++++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf.c          |  7 ++-
 tools/lib/bpf/libbpf_internal.h |  2 +
 3 files changed, 99 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
index b842b83e2480..b1a088dd83ac 100644
--- a/tools/lib/bpf/features.c
+++ b/tools/lib/bpf/features.c
@@ -506,6 +506,95 @@ static int probe_kern_arg_ctx_tag(int token_fd)
 	return probe_fd(prog_fd);
 }
 
+static int probe_kern_arena_global_reloc(int token_fd)
+{
+	const size_t bufsz = 1024;
+	int btf_fd, prog_fd, map;
+	char log_buf[bufsz];
+	int ret;
+	static const char strs[] = "\0f\0";
+	const __u32 types[] = {
+		/* [1] FUNC_PROTO `void(void)` */
+		BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 0), 0),
+		/* [2] FUNC 'f' -> FUNC_PROTO (main prog) */
+		BTF_TYPE_ENC(1 /* "f" */, BTF_INFO_ENC(BTF_KIND_FUNC, 0, BTF_FUNC_GLOBAL), 1),
+	};
+	LIBBPF_OPTS(bpf_map_create_opts, map_opts,
+		.token_fd = token_fd,
+		.map_flags = token_fd ? BPF_F_TOKEN_FD : 0,
+	);
+	LIBBPF_OPTS(bpf_prog_load_opts, prog_opts,
+		.token_fd = token_fd,
+		.prog_flags = BPF_F_SLEEPABLE | (token_fd ? BPF_F_TOKEN_FD : 0),
+		.log_buf = log_buf,
+		.log_size = bufsz,
+	);
+	struct bpf_insn insns[] = {
+		BPF_LD_MAP_VALUE(BPF_REG_1, 0, 1UL << 30),
+		BPF_EXIT_INSN(),
+	};
+	const struct bpf_func_info_min func_infos[] = {
+		{ 0, 2 }, /* main prog -> FUNC 'f' */
+	};
+	int insn_cnt = ARRAY_SIZE(insns);
+
+	btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types), strs, sizeof(strs), token_fd);
+	if (btf_fd < 0)
+		return 0; /* BTF not supported at all */
+
+	map = bpf_map_create(BPF_MAP_TYPE_ARRAY, "arr", sizeof(int), 1, 1, &map_opts);
+	if (map < 0) {
+		ret = -errno;
+		pr_warn("Error in %s(): %s. Couldn't create simple array map.\n",
+			__func__, errstr(ret));
+		close(btf_fd);
+		return ret;
+	}
+	insns[0].imm = map;
+
+	prog_opts.prog_btf_fd = btf_fd;
+	prog_opts.func_info = &func_infos;
+	prog_opts.func_info_cnt = ARRAY_SIZE(func_infos);
+	prog_opts.func_info_rec_size = sizeof(func_infos[0]);
+
+	prog_fd = bpf_prog_load(BPF_PROG_TYPE_SYSCALL, "global_reloc", "GPL", insns, insn_cnt, &prog_opts);
+
+	ret = -errno;
+	close(map);
+	close(btf_fd);
+
+	if (prog_fd >= 0) {
+		pr_warn("Error in %s(): Program loading unexpectedly succeeded.\n",
+			__func__);
+		close(prog_fd);
+		return -EINVAL;
+	}
+
+	/* Be conservative and NULL terminate the buffer to ensure strstr terminates. */
+	log_buf[bufsz - 1] = '\0';
+
+	/*
+	 * Feature is allowed if we're not failing with the error message "direct value
+	 * offset of %u is not allowed that was removed in 12a1fe6e12db
+	 * ("bpf/verifier: Do not limit maximum direct offset into arena map").
+	 * Instead, we should be failing with the message "invalid access to map value
+	 * pointer". Ensure we match with one of the two and we're not failing with a
+	 * different, unexpected message.
+	 */
+	if (strstr(log_buf, "direct value offset of"))
+		return 0;
+
+	if (strstr(log_buf, "invalid access to map value pointer") == NULL) {
+		pr_warn("Error in %s(): Program unexpectedly failed with message: %s.\n",
+			__func__, log_buf);
+		return ret;
+	}
+
+	/* Feature is on. */
+
+	return 1;
+}
+
 typedef int (*feature_probe_fn)(int /* token_fd */);
 
 static struct kern_feature_cache feature_cache;
@@ -581,6 +670,9 @@ static struct kern_feature_desc {
 	[FEAT_BTF_QMARK_DATASEC] = {
 		"BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec,
 	},
+	[FEAT_ARENA_GLOBAL_RELOC] = {
+		"Relocatable arena globals support", probe_kern_arena_global_reloc,
+	},
 };
 
 bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0c8bf0b5cce4..0aeb740a5f47 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3009,8 +3009,11 @@ static int init_arena_map_data(struct bpf_object *obj, struct bpf_map *map,
 	memcpy(obj->arena_data, data, data_sz);
 	obj->arena_data_sz = data_sz;
 
-	/* place globals at the end of the arena */
-	obj->arena_data_off = mmap_sz - data_alloc_sz;
+	/* place globals at the end of the arena (if supported) */
+	if (kernel_supports(obj, FEAT_ARENA_GLOBAL_RELOC))
+		obj->arena_data_off = mmap_sz - data_alloc_sz;
+	else
+		obj->arena_data_off = 0;
 
 	/* make bpf_map__init_value() work for ARENA maps */
 	map->mmaped = obj->arena_data;
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index fc59b21b51b5..e0223a6e4c95 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -392,6 +392,8 @@ enum kern_feature_id {
 	FEAT_ARG_CTX_TAG,
 	/* Kernel supports '?' at the front of datasec names */
 	FEAT_BTF_QMARK_DATASEC,
+	/* Kernel supports relocating arena globals to end of the arena */
+	FEAT_ARENA_GLOBAL_RELOC,
 	__FEAT_CNT,
 };
 
-- 
2.49.0

Re: [PATCH bpf-next v2] libbpf: Add gating for arena globals relocation feature

[Emil Tsalapatis]

On Mon Feb 9, 2026 at 6:48 PM EST, Emil Tsalapatis wrote:
> Add feature gating for the arena globals relocation introduced in
> commit c1f61171d44b. The commit depends on a previous commit in the
> same patchset that is absent from older kernels (12a1fe6e12db,
> "bpf/verifier: Do not limit maximum direct offset into arena map").
> Without this commit, arena globals relocation with arenas >= 512MiB
> fails to load and breaks libbpf's backwards compatibility.
>
> Introduce a libbpf feature to check whether the running kernel includes
> patch 12a1fe6e12db, and only relocate arena globals if it does.
>
> CHANGELOG
> ---------
>
> v1 -> v2 (https://lore.kernel.org/bpf/20260209210240.2051209-1-emil@etsalapatis.com/)
>
> - Reworked test to use simpler array-based program (Andrii)
>
> Fixes: c1f61171d44b ("libbpf: Move arena globals to the end of the arena")
> Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
> ---

This patch does not properly parse the verifier log for kernels without
12a1fe6e12db. Will fix and respin.

>  tools/lib/bpf/features.c        | 92 +++++++++++++++++++++++++++++++++
>  tools/lib/bpf/libbpf.c          |  7 ++-
>  tools/lib/bpf/libbpf_internal.h |  2 +
>  3 files changed, 99 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
> index b842b83e2480..b1a088dd83ac 100644
> --- a/tools/lib/bpf/features.c
> +++ b/tools/lib/bpf/features.c
> @@ -506,6 +506,95 @@ static int probe_kern_arg_ctx_tag(int token_fd)
>  	return probe_fd(prog_fd);
>  }
>  
> +static int probe_kern_arena_global_reloc(int token_fd)
> +{
> +	const size_t bufsz = 1024;
> +	int btf_fd, prog_fd, map;
> +	char log_buf[bufsz];
> +	int ret;
> +	static const char strs[] = "\0f\0";
> +	const __u32 types[] = {
> +		/* [1] FUNC_PROTO `void(void)` */
> +		BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 0), 0),
> +		/* [2] FUNC 'f' -> FUNC_PROTO (main prog) */
> +		BTF_TYPE_ENC(1 /* "f" */, BTF_INFO_ENC(BTF_KIND_FUNC, 0, BTF_FUNC_GLOBAL), 1),
> +	};
> +	LIBBPF_OPTS(bpf_map_create_opts, map_opts,
> +		.token_fd = token_fd,
> +		.map_flags = token_fd ? BPF_F_TOKEN_FD : 0,
> +	);
> +	LIBBPF_OPTS(bpf_prog_load_opts, prog_opts,
> +		.token_fd = token_fd,
> +		.prog_flags = BPF_F_SLEEPABLE | (token_fd ? BPF_F_TOKEN_FD : 0),
> +		.log_buf = log_buf,
> +		.log_size = bufsz,
> +	);
> +	struct bpf_insn insns[] = {
> +		BPF_LD_MAP_VALUE(BPF_REG_1, 0, 1UL << 30),
> +		BPF_EXIT_INSN(),
> +	};
> +	const struct bpf_func_info_min func_infos[] = {
> +		{ 0, 2 }, /* main prog -> FUNC 'f' */
> +	};
> +	int insn_cnt = ARRAY_SIZE(insns);
> +
> +	btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types), strs, sizeof(strs), token_fd);
> +	if (btf_fd < 0)
> +		return 0; /* BTF not supported at all */
> +
> +	map = bpf_map_create(BPF_MAP_TYPE_ARRAY, "arr", sizeof(int), 1, 1, &map_opts);
> +	if (map < 0) {
> +		ret = -errno;
> +		pr_warn("Error in %s(): %s. Couldn't create simple array map.\n",
> +			__func__, errstr(ret));
> +		close(btf_fd);
> +		return ret;
> +	}
> +	insns[0].imm = map;
> +
> +	prog_opts.prog_btf_fd = btf_fd;
> +	prog_opts.func_info = &func_infos;
> +	prog_opts.func_info_cnt = ARRAY_SIZE(func_infos);
> +	prog_opts.func_info_rec_size = sizeof(func_infos[0]);
> +
> +	prog_fd = bpf_prog_load(BPF_PROG_TYPE_SYSCALL, "global_reloc", "GPL", insns, insn_cnt, &prog_opts);
> +
> +	ret = -errno;
> +	close(map);
> +	close(btf_fd);
> +
> +	if (prog_fd >= 0) {
> +		pr_warn("Error in %s(): Program loading unexpectedly succeeded.\n",
> +			__func__);
> +		close(prog_fd);
> +		return -EINVAL;
> +	}
> +
> +	/* Be conservative and NULL terminate the buffer to ensure strstr terminates. */
> +	log_buf[bufsz - 1] = '\0';
> +
> +	/*
> +	 * Feature is allowed if we're not failing with the error message "direct value
> +	 * offset of %u is not allowed that was removed in 12a1fe6e12db
> +	 * ("bpf/verifier: Do not limit maximum direct offset into arena map").
> +	 * Instead, we should be failing with the message "invalid access to map value
> +	 * pointer". Ensure we match with one of the two and we're not failing with a
> +	 * different, unexpected message.
> +	 */
> +	if (strstr(log_buf, "direct value offset of"))
> +		return 0;
> +
> +	if (strstr(log_buf, "invalid access to map value pointer") == NULL) {
> +		pr_warn("Error in %s(): Program unexpectedly failed with message: %s.\n",
> +			__func__, log_buf);
> +		return ret;
> +	}
> +
> +	/* Feature is on. */
> +
> +	return 1;
> +}
> +
>  typedef int (*feature_probe_fn)(int /* token_fd */);
>  
>  static struct kern_feature_cache feature_cache;
> @@ -581,6 +670,9 @@ static struct kern_feature_desc {
>  	[FEAT_BTF_QMARK_DATASEC] = {
>  		"BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec,
>  	},
> +	[FEAT_ARENA_GLOBAL_RELOC] = {
> +		"Relocatable arena globals support", probe_kern_arena_global_reloc,
> +	},
>  };
>  
>  bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 0c8bf0b5cce4..0aeb740a5f47 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -3009,8 +3009,11 @@ static int init_arena_map_data(struct bpf_object *obj, struct bpf_map *map,
>  	memcpy(obj->arena_data, data, data_sz);
>  	obj->arena_data_sz = data_sz;
>  
> -	/* place globals at the end of the arena */
> -	obj->arena_data_off = mmap_sz - data_alloc_sz;
> +	/* place globals at the end of the arena (if supported) */
> +	if (kernel_supports(obj, FEAT_ARENA_GLOBAL_RELOC))
> +		obj->arena_data_off = mmap_sz - data_alloc_sz;
> +	else
> +		obj->arena_data_off = 0;
>  
>  	/* make bpf_map__init_value() work for ARENA maps */
>  	map->mmaped = obj->arena_data;
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index fc59b21b51b5..e0223a6e4c95 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -392,6 +392,8 @@ enum kern_feature_id {
>  	FEAT_ARG_CTX_TAG,
>  	/* Kernel supports '?' at the front of datasec names */
>  	FEAT_BTF_QMARK_DATASEC,
> +	/* Kernel supports relocating arena globals to end of the arena */
> +	FEAT_ARENA_GLOBAL_RELOC,
>  	__FEAT_CNT,
>  };
>  

Re: [PATCH bpf-next v2] libbpf: Add gating for arena globals relocation feature

[Emil Tsalapatis]

On Mon Feb 9, 2026 at 7:11 PM EST, Emil Tsalapatis wrote:
> On Mon Feb 9, 2026 at 6:48 PM EST, Emil Tsalapatis wrote:
>> Add feature gating for the arena globals relocation introduced in
>> commit c1f61171d44b. The commit depends on a previous commit in the
>> same patchset that is absent from older kernels (12a1fe6e12db,
>> "bpf/verifier: Do not limit maximum direct offset into arena map").
>> Without this commit, arena globals relocation with arenas >= 512MiB
>> fails to load and breaks libbpf's backwards compatibility.
>>
>> Introduce a libbpf feature to check whether the running kernel includes
>> patch 12a1fe6e12db, and only relocate arena globals if it does.
>>
>> CHANGELOG
>> ---------
>>
>> v1 -> v2 (https://lore.kernel.org/bpf/20260209210240.2051209-1-emil@etsalapatis.com/)
>>
>> - Reworked test to use simpler array-based program (Andrii)
>>
>> Fixes: c1f61171d44b ("libbpf: Move arena globals to the end of the arena")
>> Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
>> ---
>
> This patch does not properly parse the verifier log for kernels without
> 12a1fe6e12db. Will fix and respin.
>

Actually the patch works as intended: I thought the arena tests should
have been successful even after reverting 12a1fe6e12db, but that is not 
the case. I still missed one of Andrii's points on v2 so I'll respin
anyway.

>>  tools/lib/bpf/features.c        | 92 +++++++++++++++++++++++++++++++++
>>  tools/lib/bpf/libbpf.c          |  7 ++-
>>  tools/lib/bpf/libbpf_internal.h |  2 +
>>  3 files changed, 99 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
>> index b842b83e2480..b1a088dd83ac 100644
>> --- a/tools/lib/bpf/features.c
>> +++ b/tools/lib/bpf/features.c
>> @@ -506,6 +506,95 @@ static int probe_kern_arg_ctx_tag(int token_fd)
>>  	return probe_fd(prog_fd);
>>  }
>>  
>> +static int probe_kern_arena_global_reloc(int token_fd)
>> +{
>> +	const size_t bufsz = 1024;
>> +	int btf_fd, prog_fd, map;
>> +	char log_buf[bufsz];
>> +	int ret;
>> +	static const char strs[] = "\0f\0";
>> +	const __u32 types[] = {
>> +		/* [1] FUNC_PROTO `void(void)` */
>> +		BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 0), 0),
>> +		/* [2] FUNC 'f' -> FUNC_PROTO (main prog) */
>> +		BTF_TYPE_ENC(1 /* "f" */, BTF_INFO_ENC(BTF_KIND_FUNC, 0, BTF_FUNC_GLOBAL), 1),
>> +	};
>> +	LIBBPF_OPTS(bpf_map_create_opts, map_opts,
>> +		.token_fd = token_fd,
>> +		.map_flags = token_fd ? BPF_F_TOKEN_FD : 0,
>> +	);
>> +	LIBBPF_OPTS(bpf_prog_load_opts, prog_opts,
>> +		.token_fd = token_fd,
>> +		.prog_flags = BPF_F_SLEEPABLE | (token_fd ? BPF_F_TOKEN_FD : 0),
>> +		.log_buf = log_buf,
>> +		.log_size = bufsz,
>> +	);
>> +	struct bpf_insn insns[] = {
>> +		BPF_LD_MAP_VALUE(BPF_REG_1, 0, 1UL << 30),
>> +		BPF_EXIT_INSN(),
>> +	};
>> +	const struct bpf_func_info_min func_infos[] = {
>> +		{ 0, 2 }, /* main prog -> FUNC 'f' */
>> +	};
>> +	int insn_cnt = ARRAY_SIZE(insns);
>> +
>> +	btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types), strs, sizeof(strs), token_fd);
>> +	if (btf_fd < 0)
>> +		return 0; /* BTF not supported at all */
>> +
>> +	map = bpf_map_create(BPF_MAP_TYPE_ARRAY, "arr", sizeof(int), 1, 1, &map_opts);
>> +	if (map < 0) {
>> +		ret = -errno;
>> +		pr_warn("Error in %s(): %s. Couldn't create simple array map.\n",
>> +			__func__, errstr(ret));
>> +		close(btf_fd);
>> +		return ret;
>> +	}
>> +	insns[0].imm = map;
>> +
>> +	prog_opts.prog_btf_fd = btf_fd;
>> +	prog_opts.func_info = &func_infos;
>> +	prog_opts.func_info_cnt = ARRAY_SIZE(func_infos);
>> +	prog_opts.func_info_rec_size = sizeof(func_infos[0]);
>> +
>> +	prog_fd = bpf_prog_load(BPF_PROG_TYPE_SYSCALL, "global_reloc", "GPL", insns, insn_cnt, &prog_opts);
>> +
>> +	ret = -errno;
>> +	close(map);
>> +	close(btf_fd);
>> +
>> +	if (prog_fd >= 0) {
>> +		pr_warn("Error in %s(): Program loading unexpectedly succeeded.\n",
>> +			__func__);
>> +		close(prog_fd);
>> +		return -EINVAL;
>> +	}
>> +
>> +	/* Be conservative and NULL terminate the buffer to ensure strstr terminates. */
>> +	log_buf[bufsz - 1] = '\0';
>> +
>> +	/*
>> +	 * Feature is allowed if we're not failing with the error message "direct value
>> +	 * offset of %u is not allowed that was removed in 12a1fe6e12db
>> +	 * ("bpf/verifier: Do not limit maximum direct offset into arena map").
>> +	 * Instead, we should be failing with the message "invalid access to map value
>> +	 * pointer". Ensure we match with one of the two and we're not failing with a
>> +	 * different, unexpected message.
>> +	 */
>> +	if (strstr(log_buf, "direct value offset of"))
>> +		return 0;
>> +
>> +	if (strstr(log_buf, "invalid access to map value pointer") == NULL) {
>> +		pr_warn("Error in %s(): Program unexpectedly failed with message: %s.\n",
>> +			__func__, log_buf);
>> +		return ret;
>> +	}
>> +
>> +	/* Feature is on. */
>> +
>> +	return 1;
>> +}
>> +
>>  typedef int (*feature_probe_fn)(int /* token_fd */);
>>  
>>  static struct kern_feature_cache feature_cache;
>> @@ -581,6 +670,9 @@ static struct kern_feature_desc {
>>  	[FEAT_BTF_QMARK_DATASEC] = {
>>  		"BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec,
>>  	},
>> +	[FEAT_ARENA_GLOBAL_RELOC] = {
>> +		"Relocatable arena globals support", probe_kern_arena_global_reloc,
>> +	},
>>  };
>>  
>>  bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 0c8bf0b5cce4..0aeb740a5f47 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -3009,8 +3009,11 @@ static int init_arena_map_data(struct bpf_object *obj, struct bpf_map *map,
>>  	memcpy(obj->arena_data, data, data_sz);
>>  	obj->arena_data_sz = data_sz;
>>  
>> -	/* place globals at the end of the arena */
>> -	obj->arena_data_off = mmap_sz - data_alloc_sz;
>> +	/* place globals at the end of the arena (if supported) */
>> +	if (kernel_supports(obj, FEAT_ARENA_GLOBAL_RELOC))
>> +		obj->arena_data_off = mmap_sz - data_alloc_sz;
>> +	else
>> +		obj->arena_data_off = 0;
>>  
>>  	/* make bpf_map__init_value() work for ARENA maps */
>>  	map->mmaped = obj->arena_data;
>> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
>> index fc59b21b51b5..e0223a6e4c95 100644
>> --- a/tools/lib/bpf/libbpf_internal.h
>> +++ b/tools/lib/bpf/libbpf_internal.h
>> @@ -392,6 +392,8 @@ enum kern_feature_id {
>>  	FEAT_ARG_CTX_TAG,
>>  	/* Kernel supports '?' at the front of datasec names */
>>  	FEAT_BTF_QMARK_DATASEC,
>> +	/* Kernel supports relocating arena globals to end of the arena */
>> +	FEAT_ARENA_GLOBAL_RELOC,
>>  	__FEAT_CNT,
>>  };
>>  

Re: [PATCH bpf-next v2] libbpf: Add gating for arena globals relocation feature

[bot+bpf-ci]

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> diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
> index b842b83e2480..b1a088dd83ac 100644
> --- a/tools/lib/bpf/features.c
> +++ b/tools/lib/bpf/features.c

[ ... ]

> @@ -581,6 +670,9 @@ static struct kern_feature_desc {
>  	[FEAT_BTF_QMARK_DATASEC] = {
>  		"BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec,
>  	},
> +	[FEAT_ARENA_GLOBAL_RELOC] = {
> +		"Relocatable arena globals support", probe_kern_arena_global_reloc,
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In the v1 review, Andrii requested naming the feature based on what is
being detected rather than what the feature is used for:

    "we don't detect 'relocatable arena globals support', we detect if
    ldimm64 allows full range offsets, so call the detector as such
    (i.e., what you detect, not what for you are doing that)."

https://lore.kernel.org/bpf/CAEf4BzYz3KBUyqR+OJCMns2Edsd+Dhyij=f8cqSEyY9OG0KCdw@mail.gmail.com/

The feature name and description still describe the use case rather than
what the probe actually detects (whether ldimm64 allows full range
offsets). Should the naming be updated to reflect the detection
mechanism?

> +	},
>  };

> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index fc59b21b51b5..e0223a6e4c95 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -392,6 +392,8 @@ enum kern_feature_id {
>  	FEAT_ARG_CTX_TAG,
>  	/* Kernel supports '?' at the front of datasec names */
>  	FEAT_BTF_QMARK_DATASEC,
> +	/* Kernel supports relocating arena globals to end of the arena */
> +	FEAT_ARENA_GLOBAL_RELOC,

Same naming concern here - the comment and enum name describe the use
case rather than the actual detection mechanism.

>  	__FEAT_CNT,
>  };


---
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/21845712046

AI-authorship-score: low
AI-authorship-explanation: The commit follows established libbpf feature probe patterns with appropriate technical detail and changelog formatting typical of experienced kernel developers.
issues-found: 1
issue-severity-score: low
issue-severity-explanation: Unaddressed maintainer request regarding naming convention - feature name describes use case rather than detection mechanism as requested by Andrii Nakryiko.