Alan Maguire <alan.maguire@xxxxxxxxxx> writes:
> On 03/10/2024 00:52, Stephen Brennan wrote:
>> Currently we maintain one buffer of DATASEC entries that describe the
>> offsets for variables in the percpu ELF section. In order to make it
>> possible to output all global variables, we'll need to output a DATASEC
>> for each ELF section containing variables, and we'll need to control
>> whether or not to encode variables on a per-section basis.
>>
>> With this change, the ability to emit VARs from multiple sections is
>> technically present, but not enabled, so pahole still only emits percpu
>> variables. A subsequent change will enable emitting all global
>> variables.
>>
>> Signed-off-by: Stephen Brennan <stephen.s.brennan@xxxxxxxxxx>
>
> Some questions about shndx handling, but
>
> Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
>
>> ---
>> btf_encoder.c | 90 ++++++++++++++++++++++++++++++++-------------------
>> 1 file changed, 56 insertions(+), 34 deletions(-)
>>
>> diff --git a/btf_encoder.c b/btf_encoder.c
>> index 1872e00..2fd1648 100644
>> --- a/btf_encoder.c
>> +++ b/btf_encoder.c
>> @@ -98,6 +98,8 @@ struct elf_secinfo {
>> const char *name;
>> uint64_t sz;
>> uint32_t type;
>> + bool include;
>> + struct gobuffer secinfo;
>> };
>>
>> /*
>> @@ -107,7 +109,6 @@ struct btf_encoder {
>> struct list_head node;
>> struct btf *btf;
>> struct cu *cu;
>> - struct gobuffer percpu_secinfo;
>> const char *source_filename;
>> const char *filename;
>> struct elf_symtab *symtab;
>> @@ -124,7 +125,6 @@ struct btf_encoder {
>> uint32_t array_index_id;
>> struct elf_secinfo *secinfo;
>> size_t seccnt;
>> - size_t percpu_shndx;
>
> heh, ignore my earlier gripes about the type here since it's being
> removed now!
>
>> int encode_vars;
>> struct {
>> struct elf_function *entries;
>> @@ -784,46 +784,56 @@ static int32_t btf_encoder__add_var(struct btf_encoder *encoder, uint32_t type,
>> return id;
>> }
>>
>> -static int32_t btf_encoder__add_var_secinfo(struct btf_encoder *encoder, uint32_t type,
>> - uint32_t offset, uint32_t size)
>> +static int32_t btf_encoder__add_var_secinfo(struct btf_encoder *encoder, size_t shndx,
>> + uint32_t type, uint32_t offset, uint32_t size)
>> {
>> struct btf_var_secinfo si = {
>> .type = type,
>> .offset = offset,
>> .size = size,
>> };
>> - return gobuffer__add(&encoder->percpu_secinfo, &si, sizeof(si));
>> + return gobuffer__add(&encoder->secinfo[shndx].secinfo, &si, sizeof(si));
>> }
>>
>> int32_t btf_encoder__add_encoder(struct btf_encoder *encoder, struct btf_encoder *other)
>> {
>> - struct gobuffer *var_secinfo_buf = &other->percpu_secinfo;
>> - size_t sz = gobuffer__size(var_secinfo_buf);
>> - uint16_t nr_var_secinfo = sz / sizeof(struct btf_var_secinfo);
>> - uint32_t type_id;
>> - uint32_t next_type_id = btf__type_cnt(encoder->btf);
>> - int32_t i, id;
>> - struct btf_var_secinfo *vsi;
>> -
>> + size_t shndx;
>> if (encoder == other)
>> return 0;
>>
>> btf_encoder__add_saved_funcs(other);
>>
>> - for (i = 0; i < nr_var_secinfo; i++) {
>> - vsi = (struct btf_var_secinfo *)var_secinfo_buf->entries + i;
>> - type_id = next_type_id + vsi->type - 1; /* Type ID starts from 1 */
>> - id = btf_encoder__add_var_secinfo(encoder, type_id, vsi->offset, vsi->size);
>> - if (id < 0)
>> - return id;
>> + for (shndx = 0; shndx < other->seccnt; shndx++) {
>
> can't we start from 1 here since the first section is SHT_NULL?
Yeah, we're starting from 1 elsewhere, so I think all the other loops
should do so. Otherwise it's inconsistent. Nice catch, thanks!
Stephen
>> + struct gobuffer *var_secinfo_buf = &other->secinfo[shndx].secinfo;
>> + size_t sz = gobuffer__size(var_secinfo_buf);
>> + uint16_t nr_var_secinfo = sz / sizeof(struct btf_var_secinfo);
>> + uint32_t type_id;
>> + uint32_t next_type_id = btf__type_cnt(encoder->btf);
>> + int32_t i, id;
>> + struct btf_var_secinfo *vsi;
>> +
>> + if (strcmp(encoder->secinfo[shndx].name, other->secinfo[shndx].name)) {
>> + fprintf(stderr, "mismatched ELF sections at index %zu: \"%s\", \"%s\"\n",
>> + shndx, encoder->secinfo[shndx].name, other->secinfo[shndx].name);
>> + return -1;
>> + }
>> +
>> + for (i = 0; i < nr_var_secinfo; i++) {
>> + vsi = (struct btf_var_secinfo *)var_secinfo_buf->entries + i;
>> + type_id = next_type_id + vsi->type - 1; /* Type ID starts from 1 */
>> + id = btf_encoder__add_var_secinfo(encoder, shndx, type_id, vsi->offset, vsi->size);
>> + if (id < 0)
>> + return id;
>> + }
>> }
>>
>> return btf__add_btf(encoder->btf, other->btf);
>> }
>>
>> -static int32_t btf_encoder__add_datasec(struct btf_encoder *encoder, const char *section_name)
>> +static int32_t btf_encoder__add_datasec(struct btf_encoder *encoder, size_t shndx)
>> {
>> - struct gobuffer *var_secinfo_buf = &encoder->percpu_secinfo;
>> + struct gobuffer *var_secinfo_buf = &encoder->secinfo[shndx].secinfo;
>> + const char *section_name = encoder->secinfo[shndx].name;
>> struct btf *btf = encoder->btf;
>> size_t sz = gobuffer__size(var_secinfo_buf);
>> uint16_t nr_var_secinfo = sz / sizeof(struct btf_var_secinfo);
>> @@ -2032,12 +2042,14 @@ int btf_encoder__encode(struct btf_encoder *encoder)
>> {
>> bool should_tag_kfuncs;
>> int err;
>> + size_t shndx;
>>
>> /* for single-threaded case, saved funcs are added here */
>> btf_encoder__add_saved_funcs(encoder);
>>
>> - if (gobuffer__size(&encoder->percpu_secinfo) != 0)
>> - btf_encoder__add_datasec(encoder, PERCPU_SECTION);
>> + for (shndx = 0; shndx < encoder->seccnt; shndx++)
>
> same question here for 0 shndx
>
>
>> + if (gobuffer__size(&encoder->secinfo[shndx].secinfo))
>> + btf_encoder__add_datasec(encoder, shndx);
>>
>> /* Empty file, nothing to do, so... done! */
>> if (btf__type_cnt(encoder->btf) == 1)
>> @@ -2167,7 +2179,7 @@ static int btf_encoder__encode_cu_variables(struct btf_encoder *encoder)
>> struct tag *pos;
>> int err = -1;
>>
>> - if (encoder->percpu_shndx == 0 || !encoder->symtab)
>> + if (!encoder->symtab)
>> return 0;
>>
>> if (encoder->verbose)
>> @@ -2180,6 +2192,7 @@ static int btf_encoder__encode_cu_variables(struct btf_encoder *encoder)
>> struct llvm_annotation *annot;
>> const struct tag *tag;
>> size_t shndx, size;
>> + struct elf_secinfo *sec = NULL;
>> uint64_t addr;
>> int id;
>>
>> @@ -2211,7 +2224,9 @@ static int btf_encoder__encode_cu_variables(struct btf_encoder *encoder)
>>
>> /* Get the ELF section info for the variable */
>> shndx = get_elf_section(encoder, addr);
>> - if (shndx != encoder->percpu_shndx)
>> + if (shndx >= 0 && shndx < encoder->seccnt)
>> + sec = &encoder->secinfo[shndx];
>> + if (!sec || !sec->include)
>> continue;
>>
>> /* Convert addr to section relative */
>> @@ -2252,7 +2267,7 @@ static int btf_encoder__encode_cu_variables(struct btf_encoder *encoder)
>> size = tag__size(tag, cu);
>> if (size == 0 || size > UINT32_MAX) {
>> if (encoder->verbose)
>> - fprintf(stderr, "Ignoring %s-sized per-CPU variable '%s'...\n",
>> + fprintf(stderr, "Ignoring %s-sized variable '%s'...\n",
>> size == 0 ? "zero" : "over", name);
>> continue;
>> }
>> @@ -2289,13 +2304,14 @@ static int btf_encoder__encode_cu_variables(struct btf_encoder *encoder)
>> }
>>
>> /*
>> - * add a BTF_VAR_SECINFO in encoder->percpu_secinfo, which will be added into
>> - * encoder->types later when we add BTF_VAR_DATASEC.
>> + * Add the variable to the secinfo for the section it appears in.
>> + * Later we will generate a BTF_VAR_DATASEC for all any section with
>> + * an encoded variable.
>> */
>> - id = btf_encoder__add_var_secinfo(encoder, id, (uint32_t)addr, (uint32_t)size);
>> + id = btf_encoder__add_var_secinfo(encoder, shndx, id, (uint32_t)addr, (uint32_t)size);
>> if (id < 0) {
>> fprintf(stderr, "error: failed to encode section info for variable '%s' at addr 0x%" PRIx64 "\n",
>> - name, addr);
>> + name, addr);
>> goto out;
>> }
>> }
>> @@ -2373,6 +2389,7 @@ struct btf_encoder *btf_encoder__new(struct cu *cu, const char *detached_filenam
>> goto out_delete;
>> }
>>
>> + bool found_percpu = false;
>> for (shndx = 0; shndx < encoder->seccnt; shndx++) {
>> const char *secname = NULL;
>> Elf_Scn *sec = elf_section_by_idx(cu->elf, &shdr, shndx, &secname);
>> @@ -2383,11 +2400,14 @@ struct btf_encoder *btf_encoder__new(struct cu *cu, const char *detached_filenam
>> encoder->secinfo[shndx].name = secname;
>> encoder->secinfo[shndx].type = shdr.sh_type;
>>
>> - if (strcmp(secname, PERCPU_SECTION) == 0)
>> - encoder->percpu_shndx = shndx;
>> + if (strcmp(secname, PERCPU_SECTION) == 0) {
>> + found_percpu = true;
>> + if (encoder->encode_vars & BTF_VAR_PERCPU)
>> + encoder->secinfo[shndx].include = true;
>> + }
>> }
>>
>> - if (!encoder->percpu_shndx && encoder->verbose)
>> + if (!found_percpu && encoder->verbose)
>> printf("%s: '%s' doesn't have '%s' section\n", __func__, cu->filename, PERCPU_SECTION);
>>
>> if (btf_encoder__collect_symbols(encoder))
>> @@ -2415,12 +2435,14 @@ void btf_encoder__delete_func(struct elf_function *func)
>> void btf_encoder__delete(struct btf_encoder *encoder)
>> {
>> int i;
>> + size_t shndx;
>>
>> if (encoder == NULL)
>> return;
>>
>> btf_encoders__delete(encoder);
>> - __gobuffer__delete(&encoder->percpu_secinfo);
>> + for (shndx = 0; shndx < encoder->seccnt; shndx++)
>> + __gobuffer__delete(&encoder->secinfo[shndx].secinfo);
>> zfree(&encoder->filename);
>> zfree(&encoder->source_filename);
>> btf__free(encoder->btf);
