Date: Tue, 25 Jun 2024 18:08:49 +0530
From: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ian Rogers <irogers@...gle.com>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, akanksha@...ux.ibm.com,
        maddy@...ux.ibm.com, kjain@...ux.ibm.com, disgoel@...ux.vnet.ibm.com
Subject: Re: [V4 03/16] tools/perf: Add support to capture and parse raw
 instruction in powerpc using dso__data_read_offset utility



> On 25 Jun 2024, at 10:59 AM, Namhyung Kim <namhyung@...nel.org> wrote:
> 
> On Fri, Jun 14, 2024 at 10:56:18PM +0530, Athira Rajeev wrote:
>> Add support to capture and parse raw instruction in powerpc.
>> Currently, the perf tool infrastructure uses two ways to disassemble
>> and understand the instruction. One is objdump and other option is
>> via libcapstone.
>> 
>> Currently, the perf tool infrastructure uses "--no-show-raw-insn" option
>> with "objdump" while disassemble. Example from powerpc with this option
>> for an instruction address is:
>> 
>> Snippet from:
>> objdump  --start-address=<address> --stop-address=<address>  -d --no-show-raw-insn -C <vmlinux>
>> 
>> c0000000010224b4: lwz     r10,0(r9)
> 
> What about removing --no-show-raw-insn and parse the raw byte code in
> the output for powerpc?  I think it's better to support normal
> annotation together.
Hi Namhyung,

Yes, In the other patch in same series, I have added support for normal annotation together.
Patch 5 includes changes to work with binary code as well as mneumonic representation.

Example representation using --show-raw-insn in objdump gives result:

38 01 81 e8 ld r4,312(r1)

Patch5 has changes to use “objdump” with --show-raw-insn to read the raw instruction and also support normal annotation.
In case of data type profiling, with only sort keys, (type, typeoff) there is no need to disassemble and then get raw byte code.
Binary code can be read directly from the DSO. Compared to using objdump, directly reading from DSO will be faster in this case.
In summary, current patchset uses below approach:

1. Read directly from DSO using dso__data_read_offset if only “type, typeoff” is needed.
2. If in any case reading directly from DSO fails, fallback to using libcapstone. Using libcapstone to read is faster than objdump
3. If libcapstone is not supported, approach will use objdump. Patchset has changes to handle objdump result created with show-raw-ins in powerpc. 
4. Also for normal perf report or perf annotate, approach will use objdump

NOTE:
libcapstone is used currently only for reading raw binary code. Disassemble is currently not enabled. While attempting to do cs_disasm, observation is that some of the instructions were not identified (ex: extswsli, maddld) and it had to fallback to use objdump. Hence enabling "cs_disasm" is added in comment section as a TODO for powerpc. Patch number 13. 

Thanks
Athira

> 
>> 
>> This line "lwz r10,0(r9)" is parsed to extract instruction name,
>> registers names and offset. Also to find whether there is a memory
>> reference in the operands, "memory_ref_char" field of objdump is used.
>> For x86, "(" is used as memory_ref_char to tackle instructions of the
>> form "mov  (%rax), %rcx".
>> 
>> In case of powerpc, not all instructions using "(" are the only memory
>> instructions. Example, above instruction can also be of extended form (X
>> form) "lwzx r10,0,r19". Inorder to easy identify the instruction category
>> and extract the source/target registers, patch adds support to use raw
>> instruction for powerpc. Approach used is to read the raw instruction
>> directly from the DSO file using "dso__data_read_offset" utility which
>> is already implemented in perf infrastructure in "util/dso.c".
>> 
>> Example:
>> 
>> 38 01 81 e8     ld      r4,312(r1)
>> 
>> Here "38 01 81 e8" is the raw instruction representation. In powerpc,
>> this translates to instruction form: "ld RT,DS(RA)" and binary code
>> as:
>> 
>>   | 58 |  RT  |  RA |      DS       | |
>>   -------------------------------------
>>   0    6     11    16              30 31
>> 
>> Function "symbol__disassemble_dso" is updated to read raw instruction
>> directly from DSO using dso__data_read_offset utility. In case of
>> above example, this captures:
>> line:    38 01 81 e8
>> 
>> Signed-off-by: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
>> ---
>> tools/perf/util/disasm.c | 98 ++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 98 insertions(+)
>> 
>> diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
>> index b5fe3a7508bb..f19496133bf0 100644
>> --- a/tools/perf/util/disasm.c
>> +++ b/tools/perf/util/disasm.c
>> @@ -1586,6 +1586,91 @@ static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
>> }
>> #endif
>> 
>> +static int symbol__disassemble_dso(char *filename, struct symbol *sym,
> 
> Maybe rename to symbol__disassemble_raw() ?

This is specifically using dso__data_read_offset. Hence using symbol__disassemble_dso 
> 
>> + struct annotate_args *args)
>> +{
>> + struct annotation *notes = symbol__annotation(sym);
>> + struct map *map = args->ms.map;
>> + struct dso *dso = map__dso(map);
>> + u64 start = map__rip_2objdump(map, sym->start);
>> + u64 end = map__rip_2objdump(map, sym->end);
>> + u64 len = end - start;
>> + u64 offset;
>> + int i, count;
>> + u8 *buf = NULL;
>> + char disasm_buf[512];
>> + struct disasm_line *dl;
>> + u32 *line;
>> +
>> + /* Return if objdump is specified explicitly */
>> + if (args->options->objdump_path)
>> + return -1;
>> +
>> + pr_debug("Reading raw instruction from : %s using dso__data_read_offset\n", filename);
> 
> You may want to print the actual offset and remove the "using
> dso__data_read_offset" part.

Ok Sure
> 
> Thanks,
> Namhyung
> 
>> +
>> + buf = malloc(len);
>> + if (buf == NULL)
>> + goto err;
>> +
>> + count = dso__data_read_offset(dso, NULL, sym->start, buf, len);
>> +
>> + line = (u32 *)buf;
>> +
>> + if ((u64)count != len)
>> + goto err;
>> +
>> + /* add the function address and name */
>> + scnprintf(disasm_buf, sizeof(disasm_buf), "%#"PRIx64" <%s>:",
>> +   start, sym->name);
>> +
>> + args->offset = -1;
>> + args->line = disasm_buf;
>> + args->line_nr = 0;
>> + args->fileloc = NULL;
>> + args->ms.sym = sym;
>> +
>> + dl = disasm_line__new(args);
>> + if (dl == NULL)
>> + goto err;
>> +
>> + annotation_line__add(&dl->al, &notes->src->source);
>> +
>> + /* Each raw instruction is 4 byte */
>> + count = len/4;
>> +
>> + for (i = 0, offset = 0; i < count; i++) {
>> + args->offset = offset;
>> + sprintf(args->line, "%x", line[i]);
>> + dl = disasm_line__new(args);
>> + if (dl == NULL)
>> + goto err;
>> +
>> + annotation_line__add(&dl->al, &notes->src->source);
>> + offset += 4;
>> + }
>> +
>> + /* It failed in the middle */
>> + if (offset != len) {
>> + struct list_head *list = &notes->src->source;
>> +
>> + /* Discard all lines and fallback to objdump */
>> + while (!list_empty(list)) {
>> + dl = list_first_entry(list, struct disasm_line, al.node);
>> +
>> + list_del_init(&dl->al.node);
>> + disasm_line__free(dl);
>> + }
>> + count = -1;
>> + }
>> +
>> +out:
>> + free(buf);
>> + return count < 0 ? count : 0;
>> +
>> +err:
>> + count = -1;
>> + goto out;
>> +}
>> /*
>>  * Possibly create a new version of line with tabs expanded. Returns the
>>  * existing or new line, storage is updated if a new line is allocated. If
>> @@ -1710,6 +1795,19 @@ int symbol__disassemble(struct symbol *sym, struct annotate_args *args)
>> strcpy(symfs_filename, tmp);
>> }
>> 
>> + /*
>> +  * For powerpc data type profiling, use the dso__data_read_offset
>> +  * to read raw instruction directly and interpret the binary code
>> +  * to understand instructions and register fields. For sort keys as
>> +  * type and typeoff, disassemble to mnemonic notation is
>> +  * not required in case of powerpc.
>> +  */
>> + if (arch__is(args->arch, "powerpc")) {
>> + err = symbol__disassemble_dso(symfs_filename, sym, args);
>> + if (err == 0)
>> + goto out_remove_tmp;
>> + }
>> +
>> #ifdef HAVE_LIBCAPSTONE_SUPPORT
>> err = symbol__disassemble_capstone(symfs_filename, sym, args);
>> if (err == 0)
>> -- 
>> 2.43.0

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