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bpf: Create a new btf_name_by_offset() for non type name use case

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The current btf_name_by_offset() is returning "(anon)" type name for
the offset == 0 case and "(invalid-name-offset)" for the out-of-bound
offset case.

It fits well for the internal BTF verbose log purpose which
is focusing on type.  For example,
offset == 0 => "(anon)" => anonymous type/name.
Returning non-NULL for the bad offset case is needed
during the BTF verification process because the BTF verifier may
complain about another field first before discovering the name_off
is invalid.

However, it may not be ideal for the newer use case which does not
necessary mean type name.  For example, when logging line_info
in the BPF verifier in the next patch, it is better to log an
empty src line instead of logging "(anon)".

The existing bpf_name_by_offset() is renamed to __bpf_name_by_offset()
and static to btf.c.

A new bpf_name_by_offset() is added for generic context usage.  It
returns "\0" for name_off == 0 (note that btf->strings[0] is "\0")
and NULL for invalid offset.  It allows the caller to decide
what is the best output in its context.

The new btf_name_by_offset() is overlapped with btf_name_offset_valid().
Hence, btf_name_offset_valid() is removed from btf.h to keep the btf.h API
minimal.  The existing btf_name_offset_valid() usage in btf.c could also be
replaced later.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Martin KaFai Lau 2018-12-13 10:41:46 -08:00 committed by Alexei Starovoitov
parent 28c1272914
commit 23127b33ec
3 changed files with 22 additions and 14 deletions
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1
include/linux/btf.h
View File

@ -46,7 +46,6 @@ void btf_type_seq_show(const struct btf *btf, u32 type_id, void *obj,
struct seq_file *m);
int btf_get_fd_by_id(u32 id);
u32 btf_id(const struct btf *btf);
bool btf_name_offset_valid(const struct btf *btf, u32 offset);
bool btf_type_is_reg_int(const struct btf_type *t, u32 expected_size);
#ifdef CONFIG_BPF_SYSCALL

31
kernel/bpf/btf.c
View File

@ -474,7 +474,7 @@ static bool btf_name_valid_identifier(const struct btf *btf, u32 offset)
return !*src;
}
const char *btf_name_by_offset(const struct btf *btf, u32 offset)
static const char *__btf_name_by_offset(const struct btf *btf, u32 offset)
{
if (!offset)
return "(anon)";
@ -484,6 +484,14 @@ const char *btf_name_by_offset(const struct btf *btf, u32 offset)
return "(invalid-name-offset)";
}
const char *btf_name_by_offset(const struct btf *btf, u32 offset)
{
if (offset < btf->hdr.str_len)
return &btf->strings[offset];
return NULL;
}
const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id)
{
if (type_id > btf->nr_types)
@ -576,7 +584,7 @@ __printf(4, 5) static void __btf_verifier_log_type(struct btf_verifier_env *env,
__btf_verifier_log(log, "[%u] %s %s%s",
env->log_type_id,
btf_kind_str[kind],
btf_name_by_offset(btf, t->name_off),
__btf_name_by_offset(btf, t->name_off),
log_details ? " " : "");
if (log_details)
@ -620,7 +628,7 @@ static void btf_verifier_log_member(struct btf_verifier_env *env,
btf_verifier_log_type(env, struct_type, NULL);
__btf_verifier_log(log, "\t%s type_id=%u bits_offset=%u",
btf_name_by_offset(btf, member->name_off),
__btf_name_by_offset(btf, member->name_off),
member->type, member->offset);
if (fmt && *fmt) {
@ -1872,7 +1880,7 @@ static s32 btf_enum_check_meta(struct btf_verifier_env *env,
btf_verifier_log(env, "\t%s val=%d\n",
btf_name_by_offset(btf, enums[i].name_off),
__btf_name_by_offset(btf, enums[i].name_off),
enums[i].val);
}
@ -1896,7 +1904,8 @@ static void btf_enum_seq_show(const struct btf *btf, const struct btf_type *t,
for (i = 0; i < nr_enums; i++) {
if (v == enums[i].val) {
seq_printf(m, "%s",
btf_name_by_offset(btf, enums[i].name_off));
__btf_name_by_offset(btf,
enums[i].name_off));
return;
}
}
@ -1954,20 +1963,20 @@ static void btf_func_proto_log(struct btf_verifier_env *env,
}
btf_verifier_log(env, "%u %s", args[0].type,
btf_name_by_offset(env->btf,
args[0].name_off));
__btf_name_by_offset(env->btf,
args[0].name_off));
for (i = 1; i < nr_args - 1; i++)
btf_verifier_log(env, ", %u %s", args[i].type,
btf_name_by_offset(env->btf,
args[i].name_off));
__btf_name_by_offset(env->btf,
args[i].name_off));
if (nr_args > 1) {
const struct btf_param *last_arg = &args[nr_args - 1];
if (last_arg->type)
btf_verifier_log(env, ", %u %s", last_arg->type,
btf_name_by_offset(env->btf,
last_arg->name_off));
__btf_name_by_offset(env->btf,
last_arg->name_off));
else
btf_verifier_log(env, ", vararg");
}

4
kernel/bpf/verifier.c
View File

@ -4910,8 +4910,8 @@ static int check_btf_line(struct bpf_verifier_env *env,
goto err_free;
}
if (!btf_name_offset_valid(btf, linfo[i].line_off) ||
!btf_name_offset_valid(btf, linfo[i].file_name_off)) {
if (!btf_name_by_offset(btf, linfo[i].line_off) ||
!btf_name_by_offset(btf, linfo[i].file_name_off)) {
verbose(env, "Invalid line_info[%u].line_off or .file_name_off\n", i);
err = -EINVAL;
goto err_free;