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gdb: generate dwarf-5 index identically as worker-thread count changes

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Similar to the previous commit, this commit ensures that the dwarf-5
index files are generated identically as the number of worker-threads
changes.

Building the dwarf-5 index makes use of a closed hash table, the
bucket_hash local within debug_names::build().  Entries are added to
bucket_hash from m_name_to_value_set, which, in turn, is populated
by calls to debug_names::insert() in write_debug_names.  The insert
calls are ordered based on the entries within the cooked_index, and
the ordering within cooked_index depends on the number of worker
threads that GDB is using.

My proposal is to sort each chain within the bucket_hash closed hash
table prior to using this to build the dwarf-5 index.

The buckets within bucket_hash will always have the same ordering (for
a given GDB build with a given executable), and by sorting the chains
within each bucket, we can be sure that GDB will see each entry in a
deterministic order.

I've extended the index creation test to cover this case.

Approved-By: Tom Tromey <tom@tromey.com>
This commit is contained in:
Andrew Burgess 2023-11-27 13:19:39 +00:00
parent aff250145a
commit 3644f41dc8
2 changed files with 22 additions and 3 deletions
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17
gdb/dwarf2/index-write.c
View file

@ -454,6 +454,11 @@ public:
return strcmp (m_cstr, other.m_cstr) == 0;
}
bool operator< (const c_str_view &other) const
{
return strcmp (m_cstr, other.m_cstr) < 0;
}
/* Return the underlying C string. Note, the returned string is
only a reference with lifetime of this object. */
const char *c_str () const
@ -773,10 +778,18 @@ public:
}
for (size_t bucket_ix = 0; bucket_ix < bucket_hash.size (); ++bucket_ix)
{
const std::forward_list<hash_it_pair> &hashitlist
= bucket_hash[bucket_ix];
std::forward_list<hash_it_pair> &hashitlist = bucket_hash[bucket_ix];
if (hashitlist.empty ())
continue;
/* Sort the items within each bucket. This ensures that the
generated index files will be the same no matter the order in
which symbols were added into the index. */
hashitlist.sort ([] (const hash_it_pair &a, const hash_it_pair &b)
{
return a.it->first < b.it->first;
});
uint32_t &bucket_slot = m_bucket_table[bucket_ix];
/* The hashes array is indexed starting at 1. */
store_unsigned_integer (reinterpret_cast<gdb_byte *> (&bucket_slot),

8
gdb/testsuite/gdb.gdb/index-file.exp
View file

@ -44,6 +44,9 @@ remote_exec host "mkdir -p ${dir1}"
with_timeout_factor $timeout_factor {
gdb_test_no_output "save gdb-index $dir1" \
"create gdb-index file"
gdb_test_no_output "save gdb-index -dwarf-5 $dir1" \
"create dwarf-index files"
}
# Close GDB.
@ -140,13 +143,16 @@ if { $worker_threads > 1 } {
with_timeout_factor $timeout_factor {
gdb_test_no_output "save gdb-index $dir2" \
"create second gdb-index file"
gdb_test_no_output "save gdb-index -dwarf-5 $dir2" \
"create second dwarf-index files"
}
# Close GDB.
gdb_exit
# Now check that the index files are identical.
foreach suffix { gdb-index } {
foreach suffix { gdb-index debug_names debug_str } {
set result \
[remote_exec host \
"cmp -s \"$dir1/${index_filename_base}.${suffix}\" \"$dir2/${index_filename_base}.${suffix}\""]