Re: Why does libtracevent pkg-config detection wipe PKG_CONFIG_PATH?

["Mateusz Kowalczyk" <fuuzetsu@fuuzetsu.co.uk>]

On Wed, 29 May 2024, at 1:09 AM, James Clark wrote:
> On 27/05/2024 01:56, Mateusz Kowalczyk wrote:
>> Hi,
>> 
>> To build recent perf, I'm having to apply the below patch.
>> 
>> ```diff
>> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
>> index 7f1e016a9253..b70fef12a977 100644
>> --- a/tools/perf/Makefile.config
>> +++ b/tools/perf/Makefile.config
>> @@ -1181,7 +1181,7 @@ ifneq ($(NO_LIBTRACEEVENT),1)
>>      CFLAGS += -DHAVE_LIBTRACEEVENT $(LIBTRACEEVENT_CFLAGS)
>>      LDFLAGS += $(LIBTRACEEVENT_LDFLAGS)
>>      EXTLIBS += ${TRACEEVENTLIBS}
>> -    LIBTRACEEVENT_VERSION := $(shell PKG_CONFIG_PATH=$(LIBTRACEEVENT_DIR) $(PKG_CONFIG) --modversion libtraceevent)
>> +    LIBTRACEEVENT_VERSION := $(shell $(PKG_CONFIG) --modversion libtraceevent)
>>      LIBTRACEEVENT_VERSION_1 := $(word 1, $(subst ., ,$(LIBTRACEEVENT_VERSION)))
>>      LIBTRACEEVENT_VERSION_2 := $(word 2, $(subst ., ,$(LIBTRACEEVENT_VERSION)))
>>      LIBTRACEEVENT_VERSION_3 := $(word 3, $(subst ., ,$(LIBTRACEEVENT_VERSION)))
>> ```
>> 
>> I don't understand why `PKG_CONFIG_PATH` is overwritten this way. `grep`ing for PKG_CONFIG_PATH reveals that this isn't done anywhere else in the kernel tree. All other uses of `$(PKG_CONFIG)` in the file simply invoke the tool.
>> 
>
> Hi Mateusz,
>
> If PKG_CONFIG_PATH being overwritten is an issue, I'm assuming that you
> have it set in your shell already? Is there a reason you aren't using
> the default? Or is it that your version of pkg-config doesn't like that
> var being set to an empty value?

I have PKG_CONFIG_PATH set in my shell already. I don't have LIBTRACEEVENT_DIR set.

I'm not sure if pkg-config version is relevant, presumably if PKG_CONFIG_PATH is empty then no matter the version, it'll fail to resolve anything? Maybe not. Either way, on my setup, PKG_CONFIG_PATH is set explicitly and libtraceevent.pc is on it.

```
[shana@aya:~/programming/linux/tools/perf]$ echo $PKG_CONFIG_PATH 
/nix/store/k3701zl6gmx3la7y4dnflcvf3xfy88kh-python3-3.11.9/lib/pkgconfig:/nix/store/azfzvr6qa3680a8prh3xrpjfr26zmm59-libxslt-1.1.39-dev/lib/pkgconfig:/nix/store/z91sa53zd8iscw7bsjphdk8s5b84hwpg-audit-3.1.2-dev/lib/pkgconfig:/nix/store/zk3sjrzfyjw14yy8jq9yn9nk41clf84q-elfutils-0.191-dev/lib/pkgconfig:/nix/store/hf0v7fphfvxrz8dvgv2fxh12vslwh9hs-newt-0.52.24/lib/pkgconfig:/nix/store/gms9ygkqyhw74nrhxqcm0xf2gpnqbpss-slang-2.3.3-dev/lib/pkgconfig:/nix/store/2nj2qa56cnq6shqskd9ixipc01s302wb-ncurses-6.4-dev/lib/pkgconfig:/nix/store/i4w2yc2np0lw8plxri2s2n244ywm1wfy-libtraceevent-1.8.2-dev/lib/pkgconfig:/nix/store/m35h4lw1sslg0vdqw0bjkcx5nqlv4pl2-libunwind-1.8.1-dev/lib/pkgconfig:/nix/store/j93y8jkrqjy18njpnszvsk792hn1vd89-xz-5.4.6-dev/lib/pkgconfig:/nix/store/wz1lmhhmvjxj2ipp2z5mvkydchhljggm-zlib-1.3.1-dev/lib/pkgconfig:/nix/store/0bp9inq3wd4car25n60idlfics6fajjv-openssl-3.0.13-dev/lib/pkgconfig:/nix/store/6a5ryz1dbq8n79qkgcvikgm3c4fmkp05-numactl-2.0.18-dev/lib/pkgconfig:/nix/store/wwg6376ymkhpjxy6c3w9gkbhv6l2gmqy-libxcrypt-4.4.36/lib/pkgconfig:/nix/store/ijj4lm5k5vg7fzf3w3cbpgfc98d1b01a-babeltrace-1.5.8/lib/pkgconfig:/nix/store/z2jqrpg85lkh7v9bpz24nsmac1lhs5bs-zstd-1.5.6-dev/lib/pkgconfig:/nix/store/j3hdndafs2ixbh1bhv95g6pj4bankd1i-libcap-2.69-dev/lib/pkgconfig:/nix/store/srmzd01br39m4w52v9zb66v4ghlxsxfg-attr-2.5.2-dev/lib/pkgconfig

[shana@aya:~/programming/linux/tools/perf]$ pkg-config --version
0.29.2
```

>> Of course, I do actually have `libtraceevent.pc` available, it's just that `LIBTRACEVENT_DIR` is empty which stops it from finding it.
>> 
>> ```
>> [shana@aya:~/programming/linux/tools/perf]$ pkg-config --modversion libtraceevent
>> 1.8.2
>> ```
>> 
>> If I do not apply the patch, I'm getting the below errors during build.
>> 
>> I'm not sure how others are getting it to build, maybe I'm doing something wrong? Please let me know. If the diff is fine, it'd be great if anyone could apply it.
>> 
>
> I think your diff needs a small change. I'm assuming it was done this
> way to allow the custom libtraceevent path to be specified with
> LIBTRACEEVENT_DIR. If you remove that then it can't be done anymore.
>
> Isn't the right change to set PKG_CONFIG_PATH if LIBTRACEEVENT_DIR is
> set, but otherwise leave it unset?

I think that sounds right. I'm not sure what that looks like in `Make` but if no-one is up to making the change, I can attempt it at least...

> But yes the build is working fine for me.

How does it work? Presumably you either must have LIBTRACEEVENT_DIR set or your pkg-config is able to find libraries even with empty PKG_CONFIG_PATH. The latter would explain some things. On my setup at least, there are no "global" default search locations and PKG_CONFIG_PATH basically determines all the library locations. Maybe that's the difference. I guess it's easy to verify, if you run `PKG_CONFIG_PATH= pkg-config --modversion libtraceevent` then I must assume that it returns something on your setup.

> James
>
>
>> Thanks!
>> 
>> ```
>> Perhaps you should add the directory containing `libtraceevent.pc'
>> to the PKG_CONFIG_PATH environment variable
>> No package 'libtraceevent' found
>> expr: syntax error: unexpected argument ‘255’
>> 
>> Auto-detecting system features:
>> ...                                   dwarf: [ on  ]
>> ...                      dwarf_getlocations: [ on  ]
>> ...                                   glibc: [ on  ]
>> ...                                  libbfd: [ on  ]
>> ...                          libbfd-buildid: [ on  ]
>> ...                                  libcap: [ on  ]
>> ...                                  libelf: [ on  ]
>> ...                                 libnuma: [ on  ]
>> ...                  numa_num_possible_cpus: [ on  ]
>> ...                                 libperl: [ on  ]
>> ...                               libpython: [ on  ]
>> ...                               libcrypto: [ on  ]
>> ...                               libunwind: [ on  ]
>> ...                      libdw-dwarf-unwind: [ on  ]
>> ...                             libcapstone: [ OFF ]
>> ...                                    zlib: [ on  ]
>> ...                                    lzma: [ on  ]
>> ...                               get_cpuid: [ on  ]
>> ...                                     bpf: [ on  ]
>> ...                                  libaio: [ on  ]
>> ...                                 libzstd: [ on  ]
>> 
>>   INSTALL libsubcmd_headers
>>   PERF_VERSION = 6.10.rc1.g1613e604df0c
>>   GEN     perf-archive
>>   GEN     perf-iostat
>>   INSTALL libsymbol_headers
>>   INSTALL libapi_headers
>>   INSTALL libperf_headers
>>   INSTALL libbpf_headers
>>   TEST    pmu-events/metric_test.log
>>   CC      builtin-bench.o
>>   CC      builtin-annotate.o
>>   CC      builtin-config.o
>>   CC      builtin-diff.o
>>   CC      builtin-evlist.o
>>   CC      builtin-ftrace.o
>>   CC      builtin-help.o
>>   CC      builtin-buildid-list.o
>>   CC      builtin-buildid-cache.o
>>   CC      builtin-kallsyms.o
>>   CC      builtin-list.o
>>   GEN     pmu-events/pmu-events.c
>> In file included from util/session.h:5,
>>                  from builtin-buildid-list.c:17:
>> util/trace-event.h:152:62: error: operator '&&' has no right operand
>>   152 | #if defined(LIBTRACEEVENT_VERSION) &&  LIBTRACEEVENT_VERSION >= MAKE_LIBTRACEEVENT_VERSION(1, 5, 0)
>>       |                                                              ^~
>> In file included from util/session.h:5,
>>                  from builtin-evlist.c:15:
>> util/trace-event.h:152:62: error: operator '&&' has no right operand
>>   152 | #if defined(LIBTRACEEVENT_VERSION) &&  LIBTRACEEVENT_VERSION >= MAKE_LIBTRACEEVENT_VERSION(1, 5, 0)
>>       |                                                              ^~
>> In file included from util/session.h:5,
>>                  from builtin-buildid-cache.c:24:
>> util/trace-event.h:152:62: error: operator '&&' has no right operand
>>   152 | #if defined(LIBTRACEEVENT_VERSION) &&  LIBTRACEEVENT_VERSION >= MAKE_LIBTRACEEVENT_VERSION(1, 5, 0)
>>       |                                                              ^~
>>   CC      builtin-record.o
>> In file included from util/session.h:5,
>>                  from builtin-diff.c:15:
>> util/trace-event.h:152:62: error: operator '&&' has no right operand
>>   152 | #if defined(LIBTRACEEVENT_VERSION) &&  LIBTRACEEVENT_VERSION >= MAKE_LIBTRACEEVENT_VERSION(1, 5, 0)
>>       |                                                              ^~
>>   CC      builtin-report.o
>>   CC      builtin-stat.o
>> make[3]: *** [/home/shana/programming/linux/tools/build/Makefile.build:105: builtin-buildid-list.o] Error 1
>> make[3]: *** Waiting for unfinished jobs....
>> make[3]: *** [/home/shana/programming/linux/tools/build/Makefile.build:105: builtin-evlist.o] Error 1
>> In file included from util/session.h:5,
>>                  from builtin-annotate.c:32:
>> util/trace-event.h:152:62: error: operator '&&' has no right operand
>>   152 | #if defined(LIBTRACEEVENT_VERSION) &&  LIBTRACEEVENT_VERSION >= MAKE_LIBTRACEEVENT_VERSION(1, 5, 0)
>>       |                                                              ^~
>> make[3]: *** [/home/shana/programming/linux/tools/build/Makefile.build:105: builtin-buildid-cache.o] Error 1
>> make[3]: *** [/home/shana/programming/linux/tools/build/Makefile.build:105: builtin-annotate.o] Error 1
>> make[3]: *** [/home/shana/programming/linux/tools/build/Makefile.build:105: builtin-diff.o] Error 1
>> In file included from util/session.h:5,
>>                  from builtin-record.c:27:
>> util/trace-event.h:152:62: error: operator '&&' has no right operand
>>   152 | #if defined(LIBTRACEEVENT_VERSION) &&  LIBTRACEEVENT_VERSION >= MAKE_LIBTRACEEVENT_VERSION(1, 5, 0)
>>       |                                                              ^~
>> In file included from util/session.h:5,
>>                  from builtin-stat.c:60:
>> util/trace-event.h:152:62: error: operator '&&' has no right operand
>>   152 | #if defined(LIBTRACEEVENT_VERSION) &&  LIBTRACEEVENT_VERSION >= MAKE_LIBTRACEEVENT_VERSION(1, 5, 0)
>>       |                                                              ^~
>> In file included from util/session.h:5,
>>                  from builtin-report.c:35:
>> util/trace-event.h:152:62: error: operator '&&' has no right operand
>>   152 | #if defined(LIBTRACEEVENT_VERSION) &&  LIBTRACEEVENT_VERSION >= MAKE_LIBTRACEEVENT_VERSION(1, 5, 0)
>>       |                                                              ^~
>> make[3]: *** [/home/shana/programming/linux/tools/build/Makefile.build:105: builtin-record.o] Error 1
>> make[3]: *** [/home/shana/programming/linux/tools/build/Makefile.build:105: builtin-report.o] Error 1
>> make[3]: *** [/home/shana/programming/linux/tools/build/Makefile.build:105: builtin-stat.o] Error 1
>> make[2]: *** [Makefile.perf:727: perf-in.o] Error 2
>> make[2]: *** Waiting for unfinished jobs....
>>   CC      pmu-events/pmu-events.o
>>   LD      pmu-events/pmu-events-in.o
>> make[1]: *** [Makefile.perf:264: sub-make] Error 2
>> make: *** [Makefile:70: all] Error 2
>> perf version 6.10.rc1.g5f00d82dec63
>> 
>> ```
>> 
>> --
>> Mateusz K.

Thanks!

--
Mateusz K