* [PATCH bpf-next v2] bpftool: Compute map size of light skeletons at runtime
@ 2026-09-14 15:33 Leon Hwang
2026-09-14 16:39 ` bot+bpf-ci
0 siblings, 1 reply; 3+ messages in thread
From: Leon Hwang @ 2026-09-14 15:33 UTC (permalink / raw)
To: bpf
Cc: Quentin Monnet, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi,
Martin KaFai Lau, Song Liu, Yonghong Song, Jiri Olsa,
Emil Tsalapatis, Ihor Solodrai, linux-kernel, Leon Hwang
bpftool rounds memory-mapped data map sizes to the host page size when
generating a light skeleton. The generated code therefore uses a 64K
mapping size when bpftool runs on a 64K-page host, even if the skeleton
runs on a 4K-page target. The target rejects the oversized map mmap(),
causing failure of loading the light skeleton.
When try to run 64K-page selftests on 4K-page VM, the error message does
not provide the reason about page size.
test_atomics:PASS:atomics skeleton open 0 nsec
test_atomics:FAIL:atomics skeleton load unexpected error: -12 (errno 22)
#15 atomics:FAIL
Pass the original map value size and max entries to the generated code and
round mmap size to the runtime page size in the user-space light
skeleton helpers. This keeps generated light skeletons independent of the
build host page size.
Fixes: d510296d331a ("bpftool: Use syscall/loader program in "prog load" and "gen skeleton" command.")
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
v1 -> v2:
* Pass max entries alongside value size.
* Use the computed mmap size for mprotect() in userspace's
skel_protect_map_data().
* Round up the mmap size to page size with keeping the original
multiplying max_entries logic. (Andrii)
* v1: https://lore.kernel.org/bpf/20260911145914.23676-1-leon.hwang@linux.dev/
---
tools/bpf/bpftool/gen.c | 26 +++++++--------------
tools/lib/bpf/skel_internal.h | 43 +++++++++++++++++++++++------------
2 files changed, 37 insertions(+), 32 deletions(-)
diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index a50540ef6521..ee680f7c2116 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -500,16 +500,6 @@ static void print_hex(const char *data, int data_sz)
}
}
-static size_t bpf_map_mmap_sz(const struct bpf_map *map)
-{
- long page_sz = sysconf(_SC_PAGE_SIZE);
- size_t map_sz;
-
- map_sz = (size_t)roundup(bpf_map__value_size(map), 8) * bpf_map__max_entries(map);
- map_sz = roundup(map_sz, page_sz);
- return map_sz;
-}
-
/* Emit type size asserts for all top-level fields in memory-mapped internal maps. */
static void codegen_asserts(struct bpf_object *obj, const char *obj_name)
{
@@ -686,8 +676,8 @@ static void codegen_destroy(struct bpf_object *obj, const char *obj_name)
if (!get_map_ident(map, ident, sizeof(ident)))
continue;
if (is_skel_data(map, ident, sizeof(ident)))
- printf("\tskel_free_map_data(skel->%1$s, skel->maps.%1$s.initial_value, %2$zu);\n",
- ident, bpf_map_mmap_sz(map));
+ printf("\tskel_free_map_data(skel->%1$s, skel->maps.%1$s.initial_value, %2$u, %3$u);\n",
+ ident, bpf_map__value_size(map), bpf_map__max_entries(map));
codegen("\
\n\
skel_closenz(skel->maps.%1$s.map_fd); \n\
@@ -771,13 +761,13 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
\n\
\"; \n\
\n\
- skel->%1$s = (__typeof__(skel->%1$s))skel_prep_map_data((void *)data, %2$zd,\n\
+ skel->%1$s = (__typeof__(skel->%1$s))skel_prep_map_data((void *)data, %2$u, %3$u,\n\
sizeof(data) - 1);\n\
if (!skel->%1$s) \n\
goto cleanup; \n\
skel->maps.%1$s.initial_value = (__u64) (long) skel->%1$s;\n\
} \n\
- ", ident, bpf_map_mmap_sz(map));
+ ", ident, bpf_map__value_size(map), bpf_map__max_entries(map));
}
codegen("\
\n\
@@ -871,14 +861,14 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
if (bpf_map__type(map) == BPF_MAP_TYPE_PERCPU_ARRAY) {
codegen("\
\n\
- err = skel_protect_map_data(skel->%1$s, &skel->maps.%1$s.initial_value, %2$zd);\n\
+ err = skel_protect_map_data(skel->%1$s, &skel->maps.%1$s.initial_value, %2$u, %3$u);\n\
if (err) \n\
return err; \n\
#ifdef __KERNEL__ \n\
skel->%1$s = NULL; \n\
#endif \n\
",
- ident, bpf_map_mmap_sz(map));
+ ident, bpf_map__value_size(map), bpf_map__max_entries(map));
continue;
}
@@ -890,11 +880,11 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
codegen("\
\n\
skel->%1$s = (__typeof__(skel->%1$s))skel_finalize_map_data(&skel->maps.%1$s.initial_value,\n\
- %2$zd, %3$s, skel->maps.%1$s.map_fd);\n\
+ %2$u, %3$u, %4$s, skel->maps.%1$s.map_fd);\n\
if (!skel->%1$s) \n\
return -ENOMEM; \n\
",
- ident, bpf_map_mmap_sz(map), mmap_flags);
+ ident, bpf_map__value_size(map), bpf_map__max_entries(map), mmap_flags);
}
codegen("\
\n\
diff --git a/tools/lib/bpf/skel_internal.h b/tools/lib/bpf/skel_internal.h
index 1f3f332dffbe..6f23ea9410eb 100644
--- a/tools/lib/bpf/skel_internal.h
+++ b/tools/lib/bpf/skel_internal.h
@@ -11,6 +11,7 @@
#include <linux/bpf.h>
#else
#include <unistd.h>
+#include <sys/param.h>
#include <sys/syscall.h>
#include <sys/mman.h>
#include <linux/keyctl.h>
@@ -127,7 +128,7 @@ static inline void skel_free(const void *p)
* either bpf_probe_read_kernel() or bpf_copy_from_user() from initial_value
* depending on bpf_loader_ctx->flags.
*/
-static inline void skel_free_map_data(void *p, __u64 addr, size_t sz)
+static inline void skel_free_map_data(void *p, __u64 addr, size_t val_sz, __u32 max_entries)
{
if (addr != ~0ULL)
kvfree(p);
@@ -138,18 +139,20 @@ static inline void skel_free_map_data(void *p, __u64 addr, size_t sz)
*/
}
-static inline void *skel_prep_map_data(const void *val, size_t mmap_sz, size_t val_sz)
+static inline void *skel_prep_map_data(const void *val, size_t val_sz, __u32 max_entries,
+ size_t data_sz)
{
void *addr;
- addr = kvmalloc(val_sz, GFP_KERNEL);
+ addr = kvmalloc(data_sz, GFP_KERNEL);
if (!addr)
return NULL;
- memcpy(addr, val, val_sz);
+ memcpy(addr, val, data_sz);
return addr;
}
-static inline void *skel_finalize_map_data(__u64 *init_val, size_t mmap_sz, int flags, int fd)
+static inline void *skel_finalize_map_data(__u64 *init_val, size_t val_sz, __u32 max_entries,
+ int flags, int fd)
{
struct bpf_map *map;
void *addr = NULL;
@@ -172,9 +175,10 @@ static inline void *skel_finalize_map_data(__u64 *init_val, size_t mmap_sz, int
return addr;
}
-static inline int skel_protect_map_data(void *p, __u64 *init_val, size_t sz)
+static inline int skel_protect_map_data(void *p, __u64 *init_val, size_t val_sz, __u32 max_entries)
{
- (void)sz;
+ (void)val_sz;
+ (void)max_entries;
kvfree(p);
*init_val = ~0ULL;
@@ -193,25 +197,34 @@ static inline void skel_free(void *p)
free(p);
}
-static inline void skel_free_map_data(void *p, __u64 addr, size_t sz)
+static inline size_t skel_map_mmap_sz(size_t val_sz, __u32 max_entries)
{
- munmap(p, sz);
+ return roundup(roundup(val_sz, 8) * max_entries, sysconf(_SC_PAGE_SIZE));
}
-static inline void *skel_prep_map_data(const void *val, size_t mmap_sz, size_t val_sz)
+static inline void skel_free_map_data(void *p, __u64 addr, size_t val_sz, __u32 max_entries)
{
+ munmap(p, skel_map_mmap_sz(val_sz, max_entries));
+}
+
+static inline void *skel_prep_map_data(const void *val, size_t val_sz, __u32 max_entries,
+ size_t data_sz)
+{
+ size_t mmap_sz = skel_map_mmap_sz(val_sz, max_entries);
void *addr;
addr = mmap(NULL, mmap_sz, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS, -1, 0);
if (addr == (void *) -1)
return NULL;
- memcpy(addr, val, val_sz);
+ memcpy(addr, val, data_sz);
return addr;
}
-static inline void *skel_finalize_map_data(__u64 *init_val, size_t mmap_sz, int flags, int fd)
+static inline void *skel_finalize_map_data(__u64 *init_val, size_t val_sz, __u32 max_entries,
+ int flags, int fd)
{
+ size_t mmap_sz = skel_map_mmap_sz(val_sz, max_entries);
void *addr;
addr = mmap((void *) (long) *init_val, mmap_sz, flags, MAP_SHARED | MAP_FIXED, fd, 0);
@@ -220,11 +233,13 @@ static inline void *skel_finalize_map_data(__u64 *init_val, size_t mmap_sz, int
return addr;
}
-static inline int skel_protect_map_data(void *p, __u64 *init_val, size_t sz)
+static inline int skel_protect_map_data(void *p, __u64 *init_val, size_t val_sz, __u32 max_entries)
{
+ size_t mmap_sz = skel_map_mmap_sz(val_sz, max_entries);
+
(void)init_val;
- if (mprotect(p, sz, PROT_READ))
+ if (mprotect(p, mmap_sz, PROT_READ))
return -errno;
return 0;
}
--
2.55.0
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH bpf-next v2] bpftool: Compute map size of light skeletons at runtime
2026-09-14 15:33 [PATCH bpf-next v2] bpftool: Compute map size of light skeletons at runtime Leon Hwang
@ 2026-09-14 16:39 ` bot+bpf-ci
2026-09-15 2:27 ` Leon Hwang
0 siblings, 1 reply; 3+ messages in thread
From: bot+bpf-ci @ 2026-09-14 16:39 UTC (permalink / raw)
To: leon.hwang, bpf
Cc: qmo, ast, daniel, andrii, eddyz87, memxor, martin.lau, song,
yonghong.song, jolsa, emil, ihor.solodrai, linux-kernel,
leon.hwang, ast, andrii, daniel, martin.lau, eddyz87,
yonghong.song, mason, ihor.solodrai
[-- Attachment #1: Type: text/plain, Size: 3274 bytes --]
> diff --git a/tools/lib/bpf/skel_internal.h b/tools/lib/bpf/skel_internal.h
> index 1f3f332dffbe..6f23ea9410eb 100644
> --- a/tools/lib/bpf/skel_internal.h
> +++ b/tools/lib/bpf/skel_internal.h
> @@ -11,6 +11,7 @@
> #include <linux/bpf.h>
> #else
> #include <unistd.h>
> +#include <sys/param.h>
> #include <sys/syscall.h>
> #include <sys/mman.h>
> #include <linux/keyctl.h>
[ ... ]
> @@ -193,25 +197,34 @@ static inline void skel_free(void *p)
> free(p);
> }
>
> -static inline void skel_free_map_data(void *p, __u64 addr, size_t sz)
> +static inline size_t skel_map_mmap_sz(size_t val_sz, __u32 max_entries)
> {
> - munmap(p, sz);
> + return roundup(roundup(val_sz, 8) * max_entries, sysconf(_SC_PAGE_SIZE));
> }
This isn't a bug, but would it read closer to array_map_mmap_sz() to hoist
the page size into a local here? sysconf(_SC_PAGE_SIZE) is passed straight
into roundup()'s second argument, and roundup() is a macro that expands its
second argument several times in the non-constant case. The three nearby
equivalents all hoist it: the bpf_map_mmap_sz() this patch deletes from
gen.c used 'long page_sz = sysconf(_SC_PAGE_SIZE);', and libbpf's
array_map_mmap_sz() and bpf_map_mmap_sz() both open with 'const long page_sz
= sysconf(_SC_PAGE_SIZE);'. Hoisting it here would also make the helper
independent of which roundup() definition wins, and might let the new
<sys/param.h> include be dropped.
>
> -static inline void *skel_prep_map_data(const void *val, size_t mmap_sz, size_t val_sz)
> +static inline void skel_free_map_data(void *p, __u64 addr, size_t val_sz, __u32 max_entries)
> {
> + munmap(p, skel_map_mmap_sz(val_sz, max_entries));
> +}
> +
> +static inline void *skel_prep_map_data(const void *val, size_t val_sz, __u32 max_entries,
> + size_t data_sz)
> +{
> + size_t mmap_sz = skel_map_mmap_sz(val_sz, max_entries);
> void *addr;
>
> addr = mmap(NULL, mmap_sz, PROT_READ | PROT_WRITE,
> MAP_SHARED | MAP_ANONYMOUS, -1, 0);
> if (addr == (void *) -1)
> return NULL;
> - memcpy(addr, val, val_sz);
> + memcpy(addr, val, data_sz);
> return addr;
> }
>
> -static inline void *skel_finalize_map_data(__u64 *init_val, size_t mmap_sz, int flags, int fd)
> +static inline void *skel_finalize_map_data(__u64 *init_val, size_t val_sz, __u32 max_entries,
> + int flags, int fd)
> {
> + size_t mmap_sz = skel_map_mmap_sz(val_sz, max_entries);
> void *addr;
>
> addr = mmap((void *) (long) *init_val, mmap_sz, flags, MAP_SHARED | MAP_FIXED, fd, 0);
> @@ -220,11 +233,13 @@ static inline void *skel_finalize_map_data(__u64 *init_val, size_t mmap_sz, int
> return addr;
> }
>
> -static inline int skel_protect_map_data(void *p, __u64 *init_val, size_t sz)
> +static inline int skel_protect_map_data(void *p, __u64 *init_val, size_t val_sz, __u32 max_entries)
> {
> + size_t mmap_sz = skel_map_mmap_sz(val_sz, max_entries);
> +
> (void)init_val;
>
> - if (mprotect(p, sz, PROT_READ))
> + if (mprotect(p, mmap_sz, PROT_READ))
> return -errno;
> return 0;
> }
---
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/34864978845
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH bpf-next v2] bpftool: Compute map size of light skeletons at runtime
2026-09-14 16:39 ` bot+bpf-ci
@ 2026-09-15 2:27 ` Leon Hwang
0 siblings, 0 replies; 3+ messages in thread
From: Leon Hwang @ 2026-09-15 2:27 UTC (permalink / raw)
To: bot+bpf-ci, bpf
Cc: qmo, ast, daniel, andrii, eddyz87, memxor, martin.lau, song,
yonghong.song, jolsa, emil, ihor.solodrai, linux-kernel,
martin.lau, mason
On 15/9/26 00:39, bot+bpf-ci@kernel.org wrote:
>> diff --git a/tools/lib/bpf/skel_internal.h b/tools/lib/bpf/skel_internal.h
>> index 1f3f332dffbe..6f23ea9410eb 100644
>> --- a/tools/lib/bpf/skel_internal.h
>> +++ b/tools/lib/bpf/skel_internal.h
>> @@ -11,6 +11,7 @@
>> #include <linux/bpf.h>
>> #else
>> #include <unistd.h>
>> +#include <sys/param.h>
>> #include <sys/syscall.h>
>> #include <sys/mman.h>
>> #include <linux/keyctl.h>
>
> [ ... ]
>
>> @@ -193,25 +197,34 @@ static inline void skel_free(void *p)
>> free(p);
>> }
>>
>> -static inline void skel_free_map_data(void *p, __u64 addr, size_t sz)
>> +static inline size_t skel_map_mmap_sz(size_t val_sz, __u32 max_entries)
>> {
>> - munmap(p, sz);
>> + return roundup(roundup(val_sz, 8) * max_entries, sysconf(_SC_PAGE_SIZE));
>> }
>
> This isn't a bug, but would it read closer to array_map_mmap_sz() to hoist
> the page size into a local here? sysconf(_SC_PAGE_SIZE) is passed straight
> into roundup()'s second argument, and roundup() is a macro that expands its
> second argument several times in the non-constant case. The three nearby
> equivalents all hoist it: the bpf_map_mmap_sz() this patch deletes from
> gen.c used 'long page_sz = sysconf(_SC_PAGE_SIZE);', and libbpf's
> array_map_mmap_sz() and bpf_map_mmap_sz() both open with 'const long page_sz
> = sysconf(_SC_PAGE_SIZE);'. Hoisting it here would also make the helper
> independent of which roundup() definition wins, and might let the new
> <sys/param.h> include be dropped.
Good catch.
'sysconf(_SC_PAGE_SIZE)' will be calculated several times in
'roundup(roundup(val_sz, 8) * max_entries, sysconf(_SC_PAGE_SIZE))'.
printf '%s\n' \
'#include <sys/param.h>' \
'roundup(roundup(val_sz, 8) * max_entries, sysconf(_SC_PAGE_SIZE))' |
gcc -E -P -x c - |
tail -n 1
(__builtin_constant_p (sysconf(_SC_PAGESIZE)) &&
((((sysconf(_SC_PAGESIZE)) - 1) & (sysconf(_SC_PAGESIZE))) == 0) ?
((((__builtin_constant_p (8) && ((((8) - 1) & (8)) == 0) ? (((val_sz) +
(8) - 1) & ~((8) - 1)) : ((((val_sz) + ((8) - 1)) / (8)) * (8))) *
max_entries) + (sysconf(_SC_PAGESIZE)) - 1) & ~((sysconf(_SC_PAGESIZE))
- 1)) : (((((__builtin_constant_p (8) && ((((8) - 1) & (8)) == 0) ?
(((val_sz) + (8) - 1) & ~((8) - 1)) : ((((val_sz) + ((8) - 1)) / (8)) *
(8))) * max_entries) + ((sysconf(_SC_PAGESIZE)) - 1)) /
(sysconf(_SC_PAGESIZE))) * (sysconf(_SC_PAGESIZE))))
Will hoist 'sysconf(_SC_PAGE_SIZE);' and 'roundup(val_sz, 8) * max_entries'.
However, the new <sys/param.h> is needed for roundup().
Thanks,
Leon
> [...]
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-09-14 15:33 [PATCH bpf-next v2] bpftool: Compute map size of light skeletons at runtime Leon Hwang
2026-09-14 16:39 ` bot+bpf-ci
2026-09-15 2:27 ` Leon Hwang
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