在 2022年05月12日 23:16, Yonghong Song 写道:
>
>
> On 5/12/22 7:28 AM, liqiong wrote:
>> The string form of "char []" declares a single variable. It is better
>> than "char *" which creates two variables.
>
> Could you explain in details about why it is better in generated codes?
> It is not clear to me why your patch is better than the original code.
Hi there，
The string form of "char *" creates two variables in the final assembly output,
a static string, and a char pointer to the static string. Use "objdump -S -D *.o",
can find out the static string occurring at "Contents of section .rodata".
>
>>
>> Signed-off-by: liqiong <liqiong@xxxxxxxxxxxx>
>> ---
>> kernel/bpf/btf.c | 4 ++--
>> kernel/bpf/verifier.c | 2 +-
>> 2 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>> index 0918a39279f6..218a8ac73644 100644
>> --- a/kernel/bpf/btf.c
>> +++ b/kernel/bpf/btf.c
>> @@ -894,10 +894,10 @@ static const struct btf_type *btf_type_skip_qualifiers(const struct btf *btf,
>> static const char *btf_show_name(struct btf_show *show)
>> {
>> /* BTF_MAX_ITER array suffixes "[]" */
>> - const char *array_suffixes = "[][][][][][][][][][]";
>> + static const char array_suffixes[] = "[][][][][][][][][][]";
>> const char *array_suffix = &array_suffixes[strlen(array_suffixes)];
>> /* BTF_MAX_ITER pointer suffixes "*" */
>> - const char *ptr_suffixes = "**********";
>> + static const char ptr_suffixes[] = "**********";
>> const char *ptr_suffix = &ptr_suffixes[strlen(ptr_suffixes)];
>> const char *name = NULL, *prefix = "", *parens = "";
>> const struct btf_member *m = show->state.member;
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index d175b70067b3..78a090fcbc72 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -7346,7 +7346,7 @@ static int sanitize_err(struct bpf_verifier_env *env,
>> const struct bpf_reg_state *off_reg,
>> const struct bpf_reg_state *dst_reg)
>> {
>> - static const char *err = "pointer arithmetic with it prohibited for !root";
>> + static const char err[] = "pointer arithmetic with it prohibited for !root";
>> const char *op = BPF_OP(insn->code) == BPF_ADD ? "add" : "sub";
>> u32 dst = insn->dst_reg, src = insn->src_reg;
>>
--
李力琼 <13524287433>
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