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From 16277e3910c9281d807fc6d3b4ce41c62d7d265e Mon Sep 17 00:00:00 2001
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From: Jerome Marchand <jmarchan@redhat.com>
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Date: Thu, 19 May 2022 16:37:40 +0200
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Subject: [PATCH 3/3] libbpf: Allow kernel_struct_has_field to reach field in
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unnamed struct or union
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Some fields can belong to unnamed struct or union (e.g. rcu and
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rcu_users fields of task_struct). In C, they are accessed as if their
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belong directly to the parent of the unnamed struct or union but this
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is not the case for BTF.
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When looking for a field, kernel_struct_has_field should also look
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reccursively into unnamed structs or unions. That allows code such as
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the following to work as expected:
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BPF.kernel_struct_has_field('task_struct', 'rcu')
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Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
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---
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src/cc/libbpf.c | 28 ++++++++++++++++++----------
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1 file changed, 18 insertions(+), 10 deletions(-)
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diff --git a/src/cc/libbpf.c b/src/cc/libbpf.c
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index 5f7a3f68..bdfde1f5 100644
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--- a/src/cc/libbpf.c
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+++ b/src/cc/libbpf.c
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@@ -1319,12 +1319,27 @@ bool bpf_has_kernel_btf(void)
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return true;
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}
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+static int find_member_by_name(struct btf *btf, const struct btf_type *btf_type, const char *field_name) {
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+ const struct btf_member *btf_member = btf_members(btf_type);
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+ int i;
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+
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+ for (i = 0; i < btf_vlen(btf_type); i++, btf_member++) {
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+ const char *name = btf__name_by_offset(btf, btf_member->name_off);
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+ if (!strcmp(name, field_name)) {
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+ return 1;
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+ } else if (name[0] == '\0') {
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+ if (find_member_by_name(btf, btf__type_by_id(btf, btf_member->type), field_name))
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+ return 1;
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+ }
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+ }
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+ return 0;
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+}
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+
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int kernel_struct_has_field(const char *struct_name, const char *field_name)
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{
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const struct btf_type *btf_type;
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- const struct btf_member *btf_member;
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struct btf *btf;
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- int i, ret, btf_id;
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+ int ret, btf_id;
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btf = libbpf_find_kernel_btf();
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ret = libbpf_get_error(btf);
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@@ -1338,14 +1353,7 @@ int kernel_struct_has_field(const char *struct_name, const char *field_name)
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}
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btf_type = btf__type_by_id(btf, btf_id);
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- btf_member = btf_members(btf_type);
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- for (i = 0; i < btf_vlen(btf_type); i++, btf_member++) {
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- if (!strcmp(btf__name_by_offset(btf, btf_member->name_off), field_name)) {
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- ret = 1;
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- goto cleanup;
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- }
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- }
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- ret = 0;
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+ ret = find_member_by_name(btf, btf_type, field_name);
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cleanup:
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btf__free(btf);
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--
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2.38.1
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