Re: [PATCH v1 0/6] Simplify linking against tools/perf code

[Ian Rogers]

On Tue, Mar 28, 2023 at 10:12 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> On 28/03/23 19:14, Ian Rogers wrote:
> > On Tue, Mar 28, 2023 at 6:24 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
> >>
> >> On 28/03/23 04:40, Ian Rogers wrote:
> >>> When fuzzing something like parse-events, having the main function in
> >>> perf.c alongside global variables like input_name means that
> >>> input_name must be redeclared with the fuzzer function's
> >>> main. However, as the fuzzer is using the tools/perf code as a library
> >>> this causes backward linking reference that the linker may warn
> >>> about. Reorganize perf.c and perf.h to avoid potential backward
> >>> references, or so that the declaration/definition locations are more
> >>> consistent.
> >>>
> >>
> >> Seems like it could be a pain to maintain.
> >>
> >> Did you consider just adding:
> >>
> >> diff --git a/tools/perf/perf.c b/tools/perf/perf.c
> >> index 82bbe0ca858b..a75dd47d68ee 100644
> >> --- a/tools/perf/perf.c
> >> +++ b/tools/perf/perf.c
> >> @@ -456,6 +456,7 @@ static int libperf_print(enum libperf_print_level level,
> >>         return veprintf(level, verbose, fmt, ap);
> >>  }
> >>
> >> +#ifndef CUSTOM_MAIN
> >>  int main(int argc, const char **argv)
> >>  {
> >>         int err;
> >> @@ -576,3 +577,4 @@ int main(int argc, const char **argv)
> >>  out:
> >>         return 1;
> >>  }
> >> +#endif
> >>
> >
> > It's possible. Would need to make the static functions not warn about
> > being declared and not used. I still think that just aligning
> > definitions and declarations yields the most expected code and will
> > lead to fewer problems in the long run.
>
> Making perf source dependent on an unknown derivative makes
> things more complicated.
>
> If you are not going to contribute it to perf, then a
> suggestion is along the lines of the following:

There's not an issue with contribution, most of the fuzzers are very
simple. For example, here is the coresight fuzzer we run:

```
#include <fuzzer/FuzzedDataProvider.h>

extern "C" {
#include "tools/perf/util/cs-etm-decoder/cs-etm-decoder.h"
}

static void null_packet_dump(const char *) {}

extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
 FuzzedDataProvider fdp(data, size);
 int num_cpu = fdp.ConsumeIntegralInRange(1, 1024);
 struct cs_etm_decoder_params d_params;
 std::unique_ptr<struct cs_etm_trace_params[]>
     t_params(new cs_etm_trace_params[num_cpu]);

 for(int i=0; i < num_cpu; ++i) {
   t_params[i].protocol =
fdp.ConsumeIntegralInRange(static_cast<int>(CS_ETM_PROTO_ETMV3)
,

static_cast<int>(CS_ETM_PROTO_PTM));
   fdp.ConsumeData(&t_params[i].etmv4, sizeof(struct cs_etmv4_trace_params));
 }

 d_params.packet_printer = null_packet_dump;
 d_params.operation = CS_ETM_OPERATION_DECODE;
 d_params.data = NULL;
 d_params.formatted = true;
 d_params.fsyncs = false;
 d_params.hsyncs = false;
 d_params.frame_aligned = true;

 std::unique_ptr<struct cs_etm_decoder, decltype(&cs_etm_decoder__free)>
     decoder(cs_etm_decoder__new(num_cpu, &d_params, t_params.get()),
             cs_etm_decoder__free);

 if (decoder == nullptr)
   return 0;

 do {
   size_t consumed;
  uint8_t buf[1024];
   size_t len = fdp.ConsumeData(buf, sizeof(buf));

   int ret = cs_etm_decoder__process_data_block(
       decoder.get(), 0, buf, len, &consumed);
   if (ret)
     return 0;

 } while (fdp.remaining_bytes() > 0);

 return 0;
}
```
Most of the code is boiler plate around a single function call. The
issues are build support, where to put the fuzzer generated test
corpus, the code is C++, etc.

> diff --git a/tools/perf/perf.c b/tools/perf/perf.c
> index 82bbe0ca858b..6a7fe1534664 100644
> --- a/tools/perf/perf.c
> +++ b/tools/perf/perf.c
> @@ -456,7 +456,18 @@ static int libperf_print(enum libperf_print_level level,
>         return veprintf(level, verbose, fmt, ap);
>  }
>
> $ git diff
> +#ifdef CUSTOM_MAIN
> +int main(void)
> +{
> +       printf("This is not perf\n");
> +       return 0;
> +}
> +
> +int perf_main(int argc, const char **argv);
> +int perf_main(int argc, const char **argv)
> +#else
>  int main(int argc, const char **argv)
> +#endif
>  {
>         int err;
>         const char *cmd;
> $ make EXTRA_CFLAGS="-DCUSTOM_MAIN" NO_BPF_SKEL=1 -C tools/perf >/dev/null
> Warning: Kernel ABI header at 'tools/include/uapi/linux/in.h' differs from latest version at 'include/uapi/linux/in.h'
> Warning: Kernel ABI header at 'tools/arch/x86/include/asm/cpufeatures.h' differs from latest version at 'arch/x86/include/asm/cpufeatures.h'
> Warning: Kernel ABI header at 'tools/arch/arm64/include/uapi/asm/perf_regs.h' differs from latest version at 'arch/arm64/include/uapi/asm/perf_regs.h'
> Warning: Kernel ABI header at 'tools/include/linux/coresight-pmu.h' differs from latest version at 'include/linux/coresight-pmu.h'
> Makefile.config:587: No sys/sdt.h found, no SDT events are defined, please install systemtap-sdt-devel or systemtap-sdt-dev
> Makefile.config:805: Missing perl devel files. Disabling perl scripting support, please install perl-ExtUtils-Embed/libperl-dev
> Makefile.config:1046: No libbabeltrace found, disables 'perf data' CTF format support, please install libbabeltrace-dev[el]/libbabeltrace-ctf-dev
> Makefile.config:1075: No alternatives command found, you need to set JDIR= to point to the root of your Java directory
> Makefile.config:1137: libpfm4 not found, disables libpfm4 support. Please install libpfm4-dev
> $ tools/perf/perf version
> This is not perf
>

Sure, I'm aware of how the #ifdef would function. What I'm saying is
that even with a CUSTOM_MAIN ifdef, which wouldn't be necessary with
my patches as you can drop the object file, the refactoring in the
patches still makes sense.

  perf ui: Move window resize signal functions

It isn't clear why these UI functions should be in perf.c given window
resizing is a UI issue.

  perf usage: Move usage strings

The usage strings were in builtin.h and not perf.h, so the
declaration/definition didn't align. util.h declares usage(), although
the definition is in usage.c, the variables are moved to match this.

  perf header: Move perf_version_string declaration

perf_version_string is defined in header.c and so declaring it in
header.h rather than perf.h is consistent.

  perf version: Use regular verbose flag

Just remove an unnecessary global by repurposing the existing global
for the job.

  perf util: Move input_name to util

There's no reference to input_name in perf.c and so util.c is as
sensible a location. Having this be a global is something of an
encapsulation fail, but cleaning that up wasn't the point of these
patches. The variable is used in util, so reaching up a directory to
get it feels somewhat unnatural.

  perf util: Move perf_guest/host declarations

As with input_name.

Thanks,
Ian