.../selftests/bpf/libarena/include/bpf_arena_spin_lock.h | 7 +------ tools/testing/selftests/bpf/libarena/src/common.bpf.c | 7 +++++++ tools/testing/selftests/bpf/progs/arena_spin_lock.c | 7 +++++++ 3 files changed, 15 insertions(+), 6 deletions(-)
bpf_arena_spin_lock.h defines its 64KB qnodes array in the header, so
every translation unit including it emits a copy. __weak makes them all
resolve to one instance, but bpftool gen object merges only the symbols
and concatenates each input's .addr_space.1 bytes, leaving the surplus
copies unreferenced in the linked object.
libarena links ten such units, so nine copies were dead weight (bytes):
object before after
-----------------------------------------------------
.addr_space.1 in libarena.bpf.o 676200 86376
libarena.skel.h 2100123 892371
libarena_asan.skel.h 2641124 1466477
Declare qnodes in the header and let each program define it once:
libarena in src/common.bpf.c, and the arena_spin_lock test beside the
lock it guards.
Tested with test_progs -t arena_spin_lock and -t libarena.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
---
.../selftests/bpf/libarena/include/bpf_arena_spin_lock.h | 7 +------
tools/testing/selftests/bpf/libarena/src/common.bpf.c | 7 +++++++
tools/testing/selftests/bpf/progs/arena_spin_lock.c | 7 +++++++
3 files changed, 15 insertions(+), 6 deletions(-)
diff --git a/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h b/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h
index ae6b72d15bb6..71d9db610263 100644
--- a/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h
+++ b/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h
@@ -103,12 +103,7 @@ struct arena_qnode {
#define _Q_LOCKED_VAL (1U << _Q_LOCKED_OFFSET)
#define _Q_PENDING_VAL (1U << _Q_PENDING_OFFSET)
-/*
- * The qnodes are marked __weak so we can define them in the header
- * while still ensuring all compilation units use the same struct
- * instance.
- */
-struct arena_qnode __weak __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NODES];
+extern struct arena_qnode __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NODES];
static inline u32 encode_tail(int cpu, int idx)
{
diff --git a/tools/testing/selftests/bpf/libarena/src/common.bpf.c b/tools/testing/selftests/bpf/libarena/src/common.bpf.c
index 50be57213dfb..06481f2a2892 100644
--- a/tools/testing/selftests/bpf/libarena/src/common.bpf.c
+++ b/tools/testing/selftests/bpf/libarena/src/common.bpf.c
@@ -8,6 +8,13 @@ const volatile u32 zero = 0;
struct buddy __arena buddy;
+/*
+ * Storage for the queue nodes declared by bpf_arena_spin_lock.h. Each program
+ * linking the arena spinlock provides exactly one definition, so that the array
+ * is emitted once rather than once per translation unit.
+ */
+struct arena_qnode __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NODES];
+
int arena_fls(__u64 word)
{
if (!word)
diff --git a/tools/testing/selftests/bpf/progs/arena_spin_lock.c b/tools/testing/selftests/bpf/progs/arena_spin_lock.c
index cf7cda79c16c..92e75ec3844c 100644
--- a/tools/testing/selftests/bpf/progs/arena_spin_lock.c
+++ b/tools/testing/selftests/bpf/progs/arena_spin_lock.c
@@ -23,6 +23,13 @@ int cs_count;
#if defined(ENABLE_ATOMICS_TESTS) && defined(__BPF_FEATURE_ADDR_SPACE_CAST)
arena_spinlock_t __arena lock;
int test_skip = 1;
+
+/*
+ * Storage for the queue nodes declared by bpf_arena_spin_lock.h. Each program
+ * linking the arena spinlock provides exactly one definition; libarena's lives
+ * in libarena/src/common.bpf.c.
+ */
+struct arena_qnode __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NODES];
#else
int test_skip = 2;
#endif
--
2.55.0On 8/3/26 2:18 AM, Changwoo Min wrote: > bpf_arena_spin_lock.h defines its 64KB qnodes array in the header, so > every translation unit including it emits a copy. __weak makes them all > resolve to one instance, but bpftool gen object merges only the symbols > and concatenates each input's .addr_space.1 bytes, leaving the surplus > copies unreferenced in the linked object. > > libarena links ten such units, so nine copies were dead weight (bytes): > > object before after > ----------------------------------------------------- > .addr_space.1 in libarena.bpf.o 676200 86376 > libarena.skel.h 2100123 892371 > libarena_asan.skel.h 2641124 1466477 > > Declare qnodes in the header and let each program define it once: > libarena in src/common.bpf.c, and the arena_spin_lock test beside the > lock it guards. > > Tested with test_progs -t arena_spin_lock and -t libarena. > > Signed-off-by: Changwoo Min <changwoo@igalia.com> This doesn't apply cleanly, could you respin against latest bpf-next? Thanks, Daniel
Hi Daniel, On 8/17/26 6:05 PM, Daniel Borkmann wrote: > On 8/3/26 2:18 AM, Changwoo Min wrote: >> bpf_arena_spin_lock.h defines its 64KB qnodes array in the header, so >> every translation unit including it emits a copy. __weak makes them all >> resolve to one instance, but bpftool gen object merges only the symbols >> and concatenates each input's .addr_space.1 bytes, leaving the surplus >> copies unreferenced in the linked object. >> >> libarena links ten such units, so nine copies were dead weight (bytes): >> >> object before after >> ----------------------------------------------------- >> .addr_space.1 in libarena.bpf.o 676200 86376 >> libarena.skel.h 2100123 892371 >> libarena_asan.skel.h 2641124 1466477 >> >> Declare qnodes in the header and let each program define it once: >> libarena in src/common.bpf.c, and the arena_spin_lock test beside the >> lock it guards. >> >> Tested with test_progs -t arena_spin_lock and -t libarena. >> >> Signed-off-by: Changwoo Min <changwoo@igalia.com> > This doesn't apply cleanly, could you respin against latest bpf-next? Sure. I will send the v2 rebased on the HEAD of the the bpf-next tree soon. Regards. Changwoo Min > > Thanks, > Daniel >
On Mon, Aug 17, 2026 at 9:02 AM Changwoo Min <changwoo@igalia.com> wrote: > > > > Hi Daniel, > > On 8/17/26 6:05 PM, Daniel Borkmann wrote: > > On 8/3/26 2:18 AM, Changwoo Min wrote: > >> bpf_arena_spin_lock.h defines its 64KB qnodes array in the header, so > >> every translation unit including it emits a copy. __weak makes them all > >> resolve to one instance, but bpftool gen object merges only the symbols > >> and concatenates each input's .addr_space.1 bytes, leaving the surplus > >> copies unreferenced in the linked object. > >> > >> libarena links ten such units, so nine copies were dead weight (bytes): > >> > >> object before after > >> ----------------------------------------------------- > >> .addr_space.1 in libarena.bpf.o 676200 86376 > >> libarena.skel.h 2100123 892371 > >> libarena_asan.skel.h 2641124 1466477 > >> > >> Declare qnodes in the header and let each program define it once: > >> libarena in src/common.bpf.c, and the arena_spin_lock test beside the > >> lock it guards. > >> > >> Tested with test_progs -t arena_spin_lock and -t libarena. > >> > >> Signed-off-by: Changwoo Min <changwoo@igalia.com> Hi Changwoo, Sorry for the late reply, for the next version feel free to add: Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com> > > This doesn't apply cleanly, could you respin against latest bpf-next? > > Sure. I will send the v2 rebased on the HEAD of the the bpf-next tree soon. > > Regards. > Changwoo Min > > > > > Thanks, > > Daniel > > > >
On Mon Aug 17, 2026 at 7:14 PM CEST, Emil Tsalapatis wrote: > On Mon, Aug 17, 2026 at 9:02 AM Changwoo Min <changwoo@igalia.com> wrote: >> >> > >> Hi Daniel, >> >> On 8/17/26 6:05 PM, Daniel Borkmann wrote: >> > On 8/3/26 2:18 AM, Changwoo Min wrote: >> >> bpf_arena_spin_lock.h defines its 64KB qnodes array in the header, so >> >> every translation unit including it emits a copy. __weak makes them all >> >> resolve to one instance, but bpftool gen object merges only the symbols >> >> and concatenates each input's .addr_space.1 bytes, leaving the surplus >> >> copies unreferenced in the linked object. >> >> >> >> libarena links ten such units, so nine copies were dead weight (bytes): >> >> >> >> object before after >> >> ----------------------------------------------------- >> >> .addr_space.1 in libarena.bpf.o 676200 86376 >> >> libarena.skel.h 2100123 892371 >> >> libarena_asan.skel.h 2641124 1466477 >> >> >> >> Declare qnodes in the header and let each program define it once: >> >> libarena in src/common.bpf.c, and the arena_spin_lock test beside the >> >> lock it guards. >> >> >> >> Tested with test_progs -t arena_spin_lock and -t libarena. >> >> >> >> Signed-off-by: Changwoo Min <changwoo@igalia.com> > > Hi Changwoo, > > Sorry for the late reply, for the next version feel free to add: > > Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com> > Added the tag to v2 and applied, thanks. >> > This doesn't apply cleanly, could you respin against latest bpf-next? >> >> Sure. I will send the v2 rebased on the HEAD of the the bpf-next tree soon. >> >> Regards. >> Changwoo Min >> >> > >> > Thanks, >> > Daniel >> > >> >>
On Mon Aug 3, 2026 at 2:18 AM CEST, Changwoo Min wrote:
> bpf_arena_spin_lock.h defines its 64KB qnodes array in the header, so
> every translation unit including it emits a copy. __weak makes them all
> resolve to one instance, but bpftool gen object merges only the symbols
> and concatenates each input's .addr_space.1 bytes, leaving the surplus
> copies unreferenced in the linked object.
>
> libarena links ten such units, so nine copies were dead weight (bytes):
>
> object before after
> -----------------------------------------------------
> .addr_space.1 in libarena.bpf.o 676200 86376
> libarena.skel.h 2100123 892371
> libarena_asan.skel.h 2641124 1466477
>
> Declare qnodes in the header and let each program define it once:
> libarena in src/common.bpf.c, and the arena_spin_lock test beside the
> lock it guards.
>
> Tested with test_progs -t arena_spin_lock and -t libarena.
>
> Signed-off-by: Changwoo Min <changwoo@igalia.com>
> ---
This seems ok to me. I don't have better ideas. Emil, any thoughts?
> .../selftests/bpf/libarena/include/bpf_arena_spin_lock.h | 7 +------
> tools/testing/selftests/bpf/libarena/src/common.bpf.c | 7 +++++++
> tools/testing/selftests/bpf/progs/arena_spin_lock.c | 7 +++++++
> 3 files changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h b/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h
> index ae6b72d15bb6..71d9db610263 100644
> --- a/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h
> +++ b/tools/testing/selftests/bpf/libarena/include/bpf_arena_spin_lock.h
> @@ -103,12 +103,7 @@ struct arena_qnode {
> #define _Q_LOCKED_VAL (1U << _Q_LOCKED_OFFSET)
> #define _Q_PENDING_VAL (1U << _Q_PENDING_OFFSET)
>
> -/*
> - * The qnodes are marked __weak so we can define them in the header
> - * while still ensuring all compilation units use the same struct
> - * instance.
> - */
> -struct arena_qnode __weak __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NODES];
> +extern struct arena_qnode __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NODES];
>
> static inline u32 encode_tail(int cpu, int idx)
> {
> diff --git a/tools/testing/selftests/bpf/libarena/src/common.bpf.c b/tools/testing/selftests/bpf/libarena/src/common.bpf.c
> index 50be57213dfb..06481f2a2892 100644
> --- a/tools/testing/selftests/bpf/libarena/src/common.bpf.c
> +++ b/tools/testing/selftests/bpf/libarena/src/common.bpf.c
> @@ -8,6 +8,13 @@ const volatile u32 zero = 0;
>
> struct buddy __arena buddy;
>
> +/*
> + * Storage for the queue nodes declared by bpf_arena_spin_lock.h. Each program
> + * linking the arena spinlock provides exactly one definition, so that the array
> + * is emitted once rather than once per translation unit.
> + */
> +struct arena_qnode __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NODES];
> +
> int arena_fls(__u64 word)
> {
> if (!word)
> diff --git a/tools/testing/selftests/bpf/progs/arena_spin_lock.c b/tools/testing/selftests/bpf/progs/arena_spin_lock.c
> index cf7cda79c16c..92e75ec3844c 100644
> --- a/tools/testing/selftests/bpf/progs/arena_spin_lock.c
> +++ b/tools/testing/selftests/bpf/progs/arena_spin_lock.c
> @@ -23,6 +23,13 @@ int cs_count;
> #if defined(ENABLE_ATOMICS_TESTS) && defined(__BPF_FEATURE_ADDR_SPACE_CAST)
> arena_spinlock_t __arena lock;
> int test_skip = 1;
> +
> +/*
> + * Storage for the queue nodes declared by bpf_arena_spin_lock.h. Each program
> + * linking the arena spinlock provides exactly one definition; libarena's lives
> + * in libarena/src/common.bpf.c.
> + */
> +struct arena_qnode __arena __hidden qnodes[_Q_MAX_CPUS][_Q_MAX_NODES];
> #else
> int test_skip = 2;
> #endif
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