tools build: Check if gettid() is available before providing helper

Laura reported that the perf build failed in fedora when we got a glibc
that provides gettid(), which I reproduced using fedora rawhide with the
glibc-devel-2.29.9000-26.fc31.x86_64 package.

Add a feature check to avoid providing a gettid() helper in such
systems.

On a fedora rawhide system with this patch applied we now get:

  [root@7a5f55352234 perf]# grep gettid /tmp/build/perf/FEATURE-DUMP
  feature-gettid=1
  [root@7a5f55352234 perf]# cat /tmp/build/perf/feature/test-gettid.make.output
  [root@7a5f55352234 perf]# ldd /tmp/build/perf/feature/test-gettid.bin
          linux-vdso.so.1 (0x00007ffc6b1f6000)
          libc.so.6 => /lib64/libc.so.6 (0x00007f04e0a74000)
          /lib64/ld-linux-x86-64.so.2 (0x00007f04e0c47000)
  [root@7a5f55352234 perf]# nm /tmp/build/perf/feature/test-gettid.bin | grep -w gettid
                   U gettid@@GLIBC_2.30
  [root@7a5f55352234 perf]#

While on a fedora:29 system:

  [acme@quaco perf]$ grep gettid /tmp/build/perf/FEATURE-DUMP
  feature-gettid=0
  [acme@quaco perf]$ cat /tmp/build/perf/feature/test-gettid.make.output
  test-gettid.c: In function ‘main’:
  test-gettid.c:8:9: error: implicit declaration of function ‘gettid’; did you mean ‘getgid’? [-Werror=implicit-function-declaration]
    return gettid();
           ^~~~~~
           getgid
  cc1: all warnings being treated as errors
  [acme@quaco perf]$

Reported-by: Laura Abbott <labbott@redhat.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lkml.kernel.org/n/tip-yfy3ch53agmklwu9o7rlgf9c@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/build/Makefile.feature

@@ -36,6 +36,7 @@ FEATURE_TESTS_BASIC :=                  \
         fortify-source                  \
         sync-compare-and-swap           \
         get_current_dir_name            \
+        gettid				\
         glibc                           \
         gtk2                            \
         gtk2-infobar                    \

tools/build/feature/Makefile

@@ -54,6 +54,7 @@ FILES=                                          \
          test-get_cpuid.bin                     \
          test-sdt.bin                           \
          test-cxx.bin                           \
+         test-gettid.bin			\
          test-jvmti.bin				\
          test-jvmti-cmlr.bin			\
          test-sched_getcpu.bin			\
@@ -267,6 +268,9 @@ $(OUTPUT)test-sdt.bin:
 $(OUTPUT)test-cxx.bin:
 	$(BUILDXX) -std=gnu++11
 
+$(OUTPUT)test-gettid.bin:
+	$(BUILD)
+
 $(OUTPUT)test-jvmti.bin:
 	$(BUILD)
 

tools/build/feature/test-all.c

@@ -38,6 +38,10 @@
 # include "test-get_current_dir_name.c"
 #undef main
 
+#define main main_test_gettid
+# include "test-gettid.c"
+#undef main
+
 #define main main_test_glibc
 # include "test-glibc.c"
 #undef main
@@ -195,6 +199,7 @@ int main(int argc, char *argv[])
 	main_test_libelf();
 	main_test_libelf_mmap();
 	main_test_get_current_dir_name();
+	main_test_gettid();
 	main_test_glibc();
 	main_test_dwarf();
 	main_test_dwarf_getlocations();

tools/build/feature/test-gettid.c

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2019, Red Hat Inc, Arnaldo Carvalho de Melo <acme@redhat.com>
+#define _GNU_SOURCE
+#include <unistd.h>
+
+int main(void)
+{
+	return gettid();
+}
+
+#undef _GNU_SOURCE

tools/perf/Makefile.config

@@ -332,6 +332,10 @@ ifeq ($(feature-get_current_dir_name), 1)
   CFLAGS += -DHAVE_GET_CURRENT_DIR_NAME
 endif
 
+ifeq ($(feature-gettid), 1)
+  CFLAGS += -DHAVE_GETTID
+endif
+
 ifdef NO_LIBELF
   NO_DWARF := 1
   NO_DEMANGLE := 1

tools/perf/jvmti/jvmti_agent.c

@@ -45,10 +45,12 @@
 static char jit_path[PATH_MAX];
 static void *marker_addr;
 
+#ifndef HAVE_GETTID
 static inline pid_t gettid(void)
 {
 	return (pid_t)syscall(__NR_gettid);
 }
+#endif
 
 static int get_e_machine(struct jitheader *hdr)
 {