by Athira Rajeev

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Subject: Re: [PATCH V3 05/14] tools/perf: Add disasm_line__parse to parse raw instruction for powerpc

> On 8 Jun 2024, at 2:28 PM, Christophe Leroy <[email protected]> wrote:
>
>
>
> Le 06/06/2024 à 08:33, Namhyung Kim a écrit :
>> Hello,
>>
>> On Sat, Jun 01, 2024 at 11:39:32AM +0530, Athira Rajeev wrote:
>>> Currently, the perf tool infrastructure disasm_line__parse function to
>>> parse disassembled line.
>>>
>>> Example snippet from objdump:
>>> objdump --start-address=<address> --stop-address=<address> -d --no-show-raw-insn -C <vmlinux>
>>>
>>> c0000000010224b4: lwz r10,0(r9)
>>>
>>> This line "lwz r10,0(r9)" is parsed to extract instruction name,
>>> registers names and offset. In powerpc, the approach for data type
>>> profiling uses raw instruction instead of result from objdump to identify
>>> the instruction category and extract the source/target registers.
>>>
>>> Example: 38 01 81 e8 ld r4,312(r1)
>>>
>>> Here "38 01 81 e8" is the raw instruction representation. Add function
>>> "disasm_line__parse_powerpc" to handle parsing of raw instruction. Also
>>> update "struct ins" and "struct ins_operands" to save "opcode" and
>>> binary code. With the change, function captures:
>>>
>>> line -> "38 01 81 e8 ld r4,312(r1)"
>>> opcode and raw instruction "38 01 81 e8"
>>>
>>> Raw instruction is used later to extract the reg/offset fields. Macros
>>> are added to extract opcode and register fields. "struct ins_operands"
>>> and "struct ins" is updated to carry opcode and raw instruction binary
>>> code (raw_insn). Function "disasm_line__parse_powerpc fills the raw
>>> instruction hex value and opcode in newly added fields. There is no
>>> changes in existing code paths, which parses the disassembled code.
>>> The architecture using the instruction name and present approach is
>>> not altered. Since this approach targets powerpc, the macro
>>> implementation is added for powerpc as of now.
>>>
>>> Since the disasm_line__parse is used in other cases (perf annotate) and
>>> not only data tye profiling, the powerpc callback includes changes to
>>> work with binary code as well as mneumonic representation. Also in case
>>> if the DSO read fails and libcapstone is not supported, the approach
>>> fallback to use objdump as option. Hence as option, patch has changes to
>>> ensure objdump option also works well.
>>>
>>> Signed-off-by: Athira Rajeev <[email protected]>
>>> ---
>>> tools/include/linux/string.h | 2 +
>>> tools/lib/string.c | 13 ++++
>>> .../perf/arch/powerpc/annotate/instructions.c | 1 +
>>> tools/perf/arch/powerpc/util/dwarf-regs.c | 9 +++
>>> tools/perf/util/disasm.c | 63 ++++++++++++++++++-
>>> tools/perf/util/disasm.h | 7 +++
>>> 6 files changed, 94 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/tools/include/linux/string.h b/tools/include/linux/string.h
>>> index db5c99318c79..0acb1fc14e19 100644
>>> --- a/tools/include/linux/string.h
>>> +++ b/tools/include/linux/string.h
>>> @@ -46,5 +46,7 @@ extern char * __must_check skip_spaces(const char *);
>>>
>>> extern char *strim(char *);
>>>
>>> +extern void remove_spaces(char *s);
>>> +
>>> extern void *memchr_inv(const void *start, int c, size_t bytes);
>>> #endif /* _TOOLS_LINUX_STRING_H_ */
>>> diff --git a/tools/lib/string.c b/tools/lib/string.c
>>> index 8b6892f959ab..3126d2cff716 100644
>>> --- a/tools/lib/string.c
>>> +++ b/tools/lib/string.c
>>> @@ -153,6 +153,19 @@ char *strim(char *s)
>>> return skip_spaces(s);
>>> }
>>>
>>> +/*
>>> + * remove_spaces - Removes whitespaces from @s
>>> + */
>>> +void remove_spaces(char *s)
>>> +{
>>> + char *d = s;
>>> +
>>> + do {
>>> + while (*d == ' ')
>>> + ++d;
>>> + } while ((*s++ = *d++));
>>> +}
>>> +
>>> /**
>>> * strreplace - Replace all occurrences of character in string.
>>> * @s: The string to operate on.
>>> diff --git a/tools/perf/arch/powerpc/annotate/instructions.c b/tools/perf/arch/powerpc/annotate/instructions.c
>>> index a3f423c27cae..d57fd023ef9c 100644
>>> --- a/tools/perf/arch/powerpc/annotate/instructions.c
>>> +++ b/tools/perf/arch/powerpc/annotate/instructions.c
>>> @@ -55,6 +55,7 @@ static int powerpc__annotate_init(struct arch *arch, char *cpuid __maybe_unused)
>>> arch->initialized = true;
>>> arch->associate_instruction_ops = powerpc__associate_instruction_ops;
>>> arch->objdump.comment_char = '#';
>>> + annotate_opts.show_asm_raw = true;
>>> }
>>>
>>> return 0;
>>> diff --git a/tools/perf/arch/powerpc/util/dwarf-regs.c b/tools/perf/arch/powerpc/util/dwarf-regs.c
>>> index 0c4f4caf53ac..430623ca5612 100644
>>> --- a/tools/perf/arch/powerpc/util/dwarf-regs.c
>>> +++ b/tools/perf/arch/powerpc/util/dwarf-regs.c
>>> @@ -98,3 +98,12 @@ int regs_query_register_offset(const char *name)
>>> return roff->ptregs_offset;
>>> return -EINVAL;
>>> }
>>> +
>>> +#define PPC_OP(op) (((op) >> 26) & 0x3F)
>>> +#define PPC_RA(a) (((a) >> 16) & 0x1f)
>>> +#define PPC_RT(t) (((t) >> 21) & 0x1f)
>>> +#define PPC_RB(b) (((b) >> 11) & 0x1f)
>>> +#define PPC_D(D) ((D) & 0xfffe)
>>> +#define PPC_DS(DS) ((DS) & 0xfffc)
>>> +#define OP_LD 58
>>> +#define OP_STD 62
>>> diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
>>> index 3cd187f08193..61f0f1656f82 100644
>>> --- a/tools/perf/util/disasm.c
>>> +++ b/tools/perf/util/disasm.c
>>> @@ -45,6 +45,7 @@ static int call__scnprintf(struct ins *ins, char *bf, size_t size,
>>>
>>> static void ins__sort(struct arch *arch);
>>> static int disasm_line__parse(char *line, const char **namep, char **rawp);
>>> +static int disasm_line__parse_powerpc(struct disasm_line *dl);
>>>
>>> static __attribute__((constructor)) void symbol__init_regexpr(void)
>>> {
>>> @@ -844,6 +845,63 @@ static int disasm_line__parse(char *line, const char **namep, char **rawp)
>>> return -1;
>>> }
>>>
>>> +/*
>>> + * Parses the result captured from symbol__disassemble_*
>>> + * Example, line read from DSO file in powerpc:
>>> + * line: 38 01 81 e8
>>> + * opcode: fetched from arch specific get_opcode_insn
>>> + * rawp_insn: e8810138
>>> + *
>>> + * rawp_insn is used later to extract the reg/offset fields
>>> + */
>>> +#define PPC_OP(op) (((op) >> 26) & 0x3F)
>>> +
>>> +static int disasm_line__parse_powerpc(struct disasm_line *dl)
>>> +{
>>> + char *line = dl->al.line;
>>> + const char **namep = &dl->ins.name;
>>> + char **rawp = &dl->ops.raw;
>>> + char tmp, *tmp_opcode, *name_opcode = skip_spaces(line);
>>> + char *name = skip_spaces(name_opcode + 11);
>>> + int objdump = 0;
>>> +
>>> + if (strlen(line) > 11)
>>> + objdump = 1;
>>> +
>>> + if (name_opcode[0] == '\0')
>>> + return -1;
>>> +
>>> + if (objdump) {
>>> + *rawp = name + 1;
>>> + while ((*rawp)[0] != '\0' && !isspace((*rawp)[0]))
>>> + ++*rawp;
>>> + tmp = (*rawp)[0];
>>> + (*rawp)[0] = '\0';
>>> +
>>> + *namep = strdup(name);
>>> + if (*namep == NULL)
>>> + return -1;
>>> +
>>> + (*rawp)[0] = tmp;
>>> + *rawp = strim(*rawp);
>>> + } else
>>> + *namep = "";
>>> +
>>> + tmp_opcode = strdup(name_opcode);
>>> + tmp_opcode[11] = '\0';
>>> + remove_spaces(tmp_opcode);
>>> +
>>> + dl->ins.opcode = PPC_OP(strtol(tmp_opcode, NULL, 16));
>>> + if (objdump)
>>> + dl->ins.opcode = PPC_OP(be32_to_cpu(strtol(tmp_opcode, NULL, 16)));
>>> + dl->ops.opcode = dl->ins.opcode;
>>> +
>>> + dl->ops.raw_insn = strtol(tmp_opcode, NULL, 16);
>>> + if (objdump)
>>> + dl->ops.raw_insn = be32_to_cpu(strtol(tmp_opcode, NULL, 16));
>>> + return 0;
>>> +}
>>> +
>>> static void annotation_line__init(struct annotation_line *al,
>>> struct annotate_args *args,
>>> int nr)
>>> @@ -897,7 +955,10 @@ struct disasm_line *disasm_line__new(struct annotate_args *args)
>>> goto out_delete;
>>>
>>> if (args->offset != -1) {
>>> - if (disasm_line__parse(dl->al.line, &dl->ins.name, &dl->ops.raw) < 0)
>>> + if (arch__is(args->arch, "powerpc")) {
>>> + if (disasm_line__parse_powerpc(dl) < 0)
>>> + goto out_free_line;
>>> + } else if (disasm_line__parse(dl->al.line, &dl->ins.name, &dl->ops.raw) < 0)
>>> goto out_free_line;
>>>
>>> disasm_line__init_ins(dl, args->arch, &args->ms);
>>> diff --git a/tools/perf/util/disasm.h b/tools/perf/util/disasm.h
>>> index 718177fa4775..a391e1bb81f7 100644
>>> --- a/tools/perf/util/disasm.h
>>> +++ b/tools/perf/util/disasm.h
>>> @@ -43,14 +43,19 @@ struct arch {
>>>
>>> struct ins {
>>> const char *name;
>>> + int opcode;
>>
>> I don't think this is the right place as 'ins' can be shared for
>> different opcodes. IIUC it's like a class and disasm_line should
>> have a pointer instead of a copy of the arch instructions. So I'd
>> like to keep a single instance if they behave in the same way. But
>> this is a separate change.
>>
>> I guess we can move it to struct disasm_line and use helper macros when
>> we need to access the opcode. This will be helpful for other arches.
>>
>> struct disasm_line {
>> struct ins *ins;
>> struct ins_operands ops;
>> union {
>> u8 bytes[4];
>> u32 opcode;
>> } raw;
>> struct annotation_line al;
>> };
>>
>> #define PPC_OP(dl) (((dl)->raw.bytes[0] >> 2) & 0x3F)
>
> We already have a definition for PPC_OP(), see arch/powerpc/xmon/ppc.h:
>
> /* A macro to extract the major opcode from an instruction. */
> #define PPC_OP(i) (((i) >> 26) & 0x3f)
>
> By the way why do you want to split off instructions in bytes ? On
> powerpc an instruction is one (sometimes two) u32, nothing else, and if
> you start breaking that into bytes you will likely unnecessarily
> increase complexity when a param has bits on different bytes, and maybe
> also with the byte order depending whether you are running on a little
> or big endian PPC.
> See for instance arch_decode_instruction() in
> tools/objtool/arch/powerpc/decode.c

Hi Namhyung, Christophe

Thanks for the feedback.

IIUC, Namhyung's main point here is to move the "opcode" related field from "struct ins" to "structure disasm_line"
In my V3, I had opcode and raw instruction both as part of "struct ins" and "struct ins_operands".
For V4, I am moving the raw instruction related field to "structure disasm_line”. In this approach, "opcode"
won't be saved as a separate field in the structure. Instead raw instruction itself will be saved as part of the disasm_line.
And helper macros will be used to extract opcode from raw instruction, wherever needed. So the union will have "u8 bytes[4]" and "u32 raw_insn". For powerpc, "raw_insn" will be used to carry the raw insn. For other archs, depending on implementation, "u8 bytes[4]" could be used

Below saves the raw instruction (u32) itself in the union raw as part of "structure disasm_line"

struct disasm_line {
struct ins *ins;
struct ins_operands ops;
union {
u8 bytes[4];
u32 raw_insn;
} raw;
struct annotation_line al;
};

And to access opcode, use helper macro for powerpc as below:

#define PPC_OP(op) (((op) >> 26) & 0x3F)

In disasm_line__parse_powerpc which parses the line captured, initialise "dl->raw.raw_insn"
To access opcode, use "PPC_OP(dl->raw.raw_insn)"

Does this approach looks good ?

Athira
>
> By the way, why are we spreading different decoding functions in
> different tools ? Wouldn't it make sense to try and share decoding
> functions between objtool and perf for instance ?
>
> Christophe
>

Hi Christophe,

I think that's good idea to check. At this point, I am not aware of existing decoding functions in objtool and which all can be made common between perf. But after checking through, would be able to propose more on this. Can we go with current approach by having helper macros in perf now and then explore/understand the objtool side ?

Thanks
Athira
>
>
>>
>> Thanks,
>> Namhyung
>>
>>>
>>> struct ins_ops *ops;
>>> };
>>>
>>> struct ins_operands {
>>> char *raw;
>>> + int raw_insn;
>>> + int opcode;
>>> struct {
>>> char *raw;
>>> char *name;
>>> + int opcode;
>>> + int raw_insn;
>>> struct symbol *sym;
>>> u64 addr;
>>> s64 offset;
>>> @@ -62,6 +67,8 @@ struct ins_operands {
>>> struct {
>>> char *raw;
>>> char *name;
>>> + int opcode;
>>> + int raw_insn;
>>> u64 addr;
>>> bool multi_regs;
>>> } source;
>>> --
>>> 2.43.0