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bpf: Support fentry/fexit for functions with union args #5902

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bpf: Support fentry/fexit for functions with union args #5902

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cabff72
bpf: Support fentry/fexit for functions with union args
Asphaltt Sep 5, 2025
1e15f4f
selftests/bpf: Add test to access union argument in tracing program
Asphaltt Sep 5, 2025
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4 changes: 2 additions & 2 deletions kernel/bpf/btf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6762,7 +6762,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
/* skip modifiers */
while (btf_type_is_modifier(t))
t = btf_type_by_id(btf, t->type);
if (btf_type_is_small_int(t) || btf_is_any_enum(t) || __btf_type_is_struct(t))
if (btf_type_is_small_int(t) || btf_is_any_enum(t) || btf_type_is_struct(t))
/* accessing a scalar */
return true;
if (!btf_type_is_ptr(t)) {
Expand Down Expand Up @@ -7334,7 +7334,7 @@ static int __get_type_size(struct btf *btf, u32 btf_id,
if (btf_type_is_ptr(t))
/* kernel size of pointer. Not BPF's size of pointer*/
return sizeof(void *);
if (btf_type_is_int(t) || btf_is_any_enum(t) || __btf_type_is_struct(t))
if (btf_type_is_int(t) || btf_is_any_enum(t) || btf_type_is_struct(t))
return t->size;
return -EINVAL;
}
Expand Down
14 changes: 13 additions & 1 deletion net/bpf/test_run.c
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Expand Up @@ -574,6 +574,16 @@ noinline int bpf_fentry_test10(const void *a)
return (long)a;
}

typedef union {
void *arg0;
int *arg1;
} union_test_t;

noinline int bpf_fentry_test11(union_test_t t)
{
return (int)(long)t.arg0;
}

noinline void bpf_fentry_test_sinfo(struct skb_shared_info *sinfo)
{
}
Expand Down Expand Up @@ -688,6 +698,7 @@ int bpf_prog_test_run_tracing(struct bpf_prog *prog,
struct bpf_fentry_test_t arg = {};
u16 side_effect = 0, ret = 0;
int b = 2, err = -EFAULT;
union_test_t utt = {};
u32 retval = 0;

if (kattr->test.flags || kattr->test.cpu || kattr->test.batch_size)
Expand All @@ -705,7 +716,8 @@ int bpf_prog_test_run_tracing(struct bpf_prog *prog,
bpf_fentry_test7((struct bpf_fentry_test_t *)0) != 0 ||
bpf_fentry_test8(&arg) != 0 ||
bpf_fentry_test9(&retval) != 0 ||
bpf_fentry_test10((void *)0) != 0)
bpf_fentry_test10((void *)0) != 0 ||
bpf_fentry_test11(utt) != 0)
goto out;
break;
case BPF_MODIFY_RETURN:
Expand Down
12 changes: 12 additions & 0 deletions tools/testing/selftests/bpf/progs/verifier_btf_ctx_access.c
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Expand Up @@ -77,4 +77,16 @@ __naked void ctx_access_const_void_pointer_accept(void)
" ::: __clobber_all);
}

SEC("fentry/bpf_fentry_test11")
__description("btf_ctx_access union arg accept")
__success __retval(0)
__naked void ctx_access_union_arg_accept(void)
{
asm volatile (" \
r2 = *(u64 *)(r1 + 0); /* load 1st argument value (union) */\
r0 = 0; \
exit; \
" ::: __clobber_all);
}

char _license[] SEC("license") = "GPL";
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