https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96913
Bug ID: 96913
Summary: gcc-11: __gcov_merge_topn hangs
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: gcov-profile
Assignee: unassigned at gcc dot gnu.org
Reporter: slyfox at gcc dot gnu.org
CC: hubicka at gcc dot gnu.org, marxin at gcc dot gnu.org,
mliska at suse dot cz
Target Milestone: ---
The hang happens on real tauthon-2.8.2 interpreter from PR96394 (no nice
reproducer yet).
In this instance I tried to build tauthon-2.8.2 against gcc-master. It hangs
early when tries to merge topn entry:
"""
#0 0x00007fd73865e0ce in __GI___libc_read (fd=3, buf=0x406284 <__gcov_var+36>,
nbytes=4096) at ../sysdeps/unix/sysv/linux/read.c:26
#1 0x00007fd7385f0090 in __GI__IO_file_xsgetn (fp=0x1295bc0, data=<optimized
out>, n=4096) at libioP.h:948
#2 0x00007fd7385e4d1f in __GI__IO_fread (buf=0x406284 <__gcov_var+36>, size=1,
count=4096, fp=0x1295bc0) at iofread.c:38
#3 0x00007fd72ab4237e in gcov_read_words (words=2) at
../../../gcc/libgcc/../gcc/gcov-io.c:491
#4 0x00007fd72ab42483 in __gcov_read_counter () at
../../../gcc/libgcc/../gcc/gcov-io.c:528
#5 0x00007fd72ab4190e in gcov_get_counter_target () at
../../../gcc/libgcc/libgcov.h:383
#6 0x00007fd72ab41c6b in __gcov_merge_topn (counters=0x7fd72ab4d320
<__gcov4.encoder_clear>, n_counters=24) at
../../../gcc/libgcc/libgcov-merge.c:114
#7 0x00007fd72ab43569 in merge_one_data (
filename=0x1154290
"/tmp/portage/dev-lang/tauthon-2.8.2/work/x86_64-pc-linux-gnu/build/temp.linux-x86_64-2.8/tmp/portage/dev-lang/tauthon-2.8.2/work/tauthon-2.8.2/Modules/_json.gcda",
gi_ptr=0x7fd72ab4a180, summary=0x7ffde7d6e9c0) at
../../../gcc/libgcc/libgcov-driver.c:314
#8 0x00007fd72ab43b1a in dump_one_gcov (gi_ptr=0x7fd72ab4a180,
gf=0x7ffde7d6ea00, run_counted=0, run_max=125)
at ../../../gcc/libgcc/libgcov-driver.c:492
#9 0x00007fd72ab43cba in gcov_do_dump (list=0x7fd72ab4a180, run_counted=0) at
../../../gcc/libgcc/libgcov-driver.c:555
#10 0x00007fd72ab43d28 in __gcov_dump_one (root=0x7fd72ab4e5c0 <__gcov_root>)
at ../../../gcc/libgcc/libgcov-driver.c:578
#11 0x00007fd72ab43d5d in __gcov_exit () at
../../../gcc/libgcc/libgcov-driver.c:600
#12 0x00007fd738c460a3 in _dl_fini () at dl-fini.c:139
#13 0x00007fd7385af564 in __run_exit_handlers (status=0, listp=0x7fd73872a738
<__exit_funcs>, run_list_atexit=run_list_atexit@entry=true,
run_dtors=run_dtors@entry=true) at exit.c:108
#14 0x00007fd7385af70a in __GI_exit (status=<optimized out>) at exit.c:139
#15 0x00007fd73899534e in Py_Exit () from
/tmp/portage/dev-lang/tauthon-2.8.2/work/x86_64-pc-linux-gnu/libtauthon2.8.so.1.0
#16 0x00007fd738995533 in handle_system_exit () from
/tmp/portage/dev-lang/tauthon-2.8.2/work/x86_64-pc-linux-gnu/libtauthon2.8.so.1.0
#17 0x00007fd73899588e in PyErr_PrintEx () from
/tmp/portage/dev-lang/tauthon-2.8.2/work/x86_64-pc-linux-gnu/libtauthon2.8.so.1.0
#18 0x00007fd738995e44 in PyErr_Print () from
/tmp/portage/dev-lang/tauthon-2.8.2/work/x86_64-pc-linux-gnu/libtauthon2.8.so.1.0
#19 0x00007fd7389b851e in RunModule () from
/tmp/portage/dev-lang/tauthon-2.8.2/work/x86_64-pc-linux-gnu/libtauthon2.8.so.1.0
#20 0x00007fd7389b9075 in Py_Main () from
/tmp/portage/dev-lang/tauthon-2.8.2/work/x86_64-pc-linux-gnu/libtauthon2.8.so.1.0
#21 0x00000000004012ac in main ()
"""
Looks like the problem is in decoding of some tag in __gcov_merge_topn(). There
count of entries is huge:
"""
(gdb) frame 6
#6 0x00007fd72ab41c6b in __gcov_merge_topn (counters=0x7fd72ab4d320
<__gcov4.encoder_clear>, n_counters=24) at
../../../gcc/libgcc/libgcov-merge.c:114
114 gcov_type value = gcov_get_counter_target ();
(gdb) list __gcov_merge_topn
96 -- counter
97 */
98
99 void
100 __gcov_merge_topn (gcov_type *counters, unsigned n_counters)
101 {
102 gcc_assert (!(n_counters % GCOV_TOPN_MEM_COUNTERS));
103
104 for (unsigned i = 0; i < (n_counters / GCOV_TOPN_MEM_COUNTERS); i++)
105 {
(gdb)
106 /* First value is number of total executions of the profiler. */
107 gcov_type all = gcov_get_counter_ignore_scaling (-1);
108 gcov_type n = gcov_get_counter_ignore_scaling (-1);
109
110 counters[GCOV_TOPN_MEM_COUNTERS * i] += all;
111
112 for (unsigned j = 0; j < n; j++)
113 {
114 gcov_type value = gcov_get_counter_target ();
115 gcov_type count = gcov_get_counter_ignore_scaling (-1);
(gdb)
116
117 // TODO: we should use atomic here
118 gcov_topn_add_value (counters + GCOV_TOPN_MEM_COUNTERS * i,
value,
119 count, 0, 0);
120 }
121 }
122 }
123 #endif /* L_gcov_merge_topn */
124
125 #endif /* inhibit_libc */
(gdb) print n
$1 = 140325305737200
(gdb) print j
$2 = 1896248771
"""
Compiler:
"""
$ ${HOME}/dev/git/gcc-native-quick-ggdb3/gcc/xgcc
-B${HOME}/dev/git/gcc-native-quick-ggdb3/gcc -v
Reading specs from /home/slyfox/dev/git/gcc-native-quick-ggdb3/gcc/specs
COLLECT_GCC=/home/slyfox/dev/git/gcc-native-quick-ggdb3/gcc/xgcc
COLLECT_LTO_WRAPPER=/home/slyfox/dev/git/gcc-native-quick-ggdb3/gcc/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc/configure --build=x86_64-pc-linux-gnu
--host=x86_64-pc-linux-gnu --target=x86_64-pc-linux-gnu
--enable-languages=c,c++ --disable-bootstrap --with-multilib-list=m64
--prefix=/home/slyfox/dev/git/gcc-native-quick-ggdb3/../gcc-native-quick-installed-ggdb3
--disable-nls --without-isl --disable-libsanitizer --disable-libvtv
--disable-libgomp --disable-libstdcxx-pch --disable-libunwind-exceptions
CFLAGS='-O0 -ggdb3 ' CXXFLAGS='-O0 -ggdb3 ' --enable-valgrind-annotations
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.0.0 20200902 (experimental) (GCC)
"""
gcc-10 seems to be able to merge profiles.
