Date: Wed, 26 Jun 2024 09:39:05 +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 26 Jun 2024, at 12:09 AM, Namhyung Kim <namhyung@...nel.org> wrote:
> 
> On Tue, Jun 25, 2024 at 06:08:49PM +0530, Athira Rajeev wrote:
>> 
>> 
>>> 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.
> 
> Ok, that's good!
> 
> 
>> 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.
> 
> Sounds like an optimization.  Then I think you'd better handle the
> general case first and optimize later.  Probably you want to merge
> patch 3 and 4 together.
> 
> Thanks,
> Namhyung

Sure, will do that.

Thanks
Athira
> 
> 
>> 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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