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* [PATCH v2 0/6] [gdb/symtab] Fix data-races in gdb.base/index-cache.exp
@ 2023-08-02  9:52 Tom de Vries
  2023-08-02  9:53 ` [PATCH v2 1/6] [gdb/symtab] Fix data race on index_cache::m_enabled Tom de Vries
                   ` (6 more replies)
  0 siblings, 7 replies; 19+ messages in thread
From: Tom de Vries @ 2023-08-02  9:52 UTC (permalink / raw)
  To: gdb-patches

When building gdb with -fsanitize=thread, we run into a data race in
gdb.base/index-cache.exp.

Fixing this leads us to another, and so on, so each patch addresses one
particular data race, with the exception of the last patch, which extends
the test-case a bit.

The last patch, when applied without the series runs into a segfault with
target board native-extended-gdbserver, filed as PR symtab/30712, but that
seems to be fixed by a previous commit in this series.  This is the reason for
which the patch is part of this series.

The first two patches implement the approach mentioned in PR30392 comment 2:
...
The reader probably should capture the necessarily globals
on the main thread and stash them until the index has been
written.
...

The 3rd patch cannot be fixed with this approach, so it uses the packed<bool, 1>
approach:
...
-  unsigned int queued : 1;
+  packed<bool, 1> queued;
...

There's one more patch like that, I checked using pahole that the struct size
is not increased.

I spent some time convincing myself that the data races on disjoint bitfields
are not benign.  I started with reading [1], and got convinced by
"2.5 Disjoint bit manipulation" in [2].  Also [3] looked interesting, but
haven't read it in full.

Tested on x86_64-linux, with and without -fsanitize=thread.

PR symtab/30392
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30392

References:
[1] https://hacks.mozilla.org/2021/04/eliminating-data-races-in-firefox-a-technical-report/
[2] https://www.usenix.org/legacy/event/hotpar11/tech/final_files/Boehm.pdf
[3] https://bartoszmilewski.com/2020/08/11/benign-data-races-considered-harmful/

Tom de Vries (6):
  [gdb/symtab] Fix data race on index_cache::m_enabled
  [gdb/symtab] Fix data race on bfd::{cacheable,format}
  [gdb/symtab] Fix race on dwarf2_per_cu_data::{queued,is_debug_type}
  [gdb/symtab] Fix data race on bfd_last_cache
  [gdb/symtab] Fix data race on
    dwarf2_per_cu_data::{m_header_read_in,is_debug_type}
  [gdb/testsuite] Extend gdb.base/index-cache.exp

 gdb/dwarf2/cooked-index.c              | 19 ++++++++---
 gdb/dwarf2/cooked-index.h              |  3 +-
 gdb/dwarf2/index-cache.c               | 46 ++++++++++++++++++++------
 gdb/dwarf2/index-cache.h               | 25 +++++++++++++-
 gdb/dwarf2/read.c                      |  8 ++---
 gdb/dwarf2/read.h                      | 26 +++++++--------
 gdb/testsuite/gdb.base/index-cache-2.c | 24 ++++++++++++++
 gdb/testsuite/gdb.base/index-cache.c   |  6 ++--
 gdb/testsuite/gdb.base/index-cache.exp | 22 ++++++++++--
 9 files changed, 141 insertions(+), 38 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/index-cache-2.c


base-commit: 69c37f53e20dc3e0b3c179b511ff786db6ae114e
-- 
2.35.3


^ permalink raw reply	[flat|nested] 19+ messages in thread
end of thread, other threads:[~2023-08-04 15:57 UTC | newest]

Thread overview: 19+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-08-02  9:52 [PATCH v2 0/6] [gdb/symtab] Fix data-races in gdb.base/index-cache.exp Tom de Vries
2023-08-02  9:53 ` [PATCH v2 1/6] [gdb/symtab] Fix data race on index_cache::m_enabled Tom de Vries
2023-08-02 19:29   ` Tom Tromey
2023-08-04  0:08     ` Tom de Vries
2023-08-02  9:53 ` [PATCH v2 2/6] [gdb/symtab] Fix data race on bfd::{cacheable,format} Tom de Vries
2023-08-02 19:32   ` Tom Tromey
2023-08-04  0:09     ` Tom de Vries
2023-08-04 15:57       ` Tom Tromey
2023-08-02  9:53 ` [PATCH v2 3/6] [gdb/symtab] Fix race on dwarf2_per_cu_data::{queued,is_debug_type} Tom de Vries
2023-08-02 19:34   ` [PATCH v2 3/6] [gdb/symtab] Fix race on dwarf2_per_cu_data::{queued, is_debug_type} Tom Tromey
2023-08-02  9:53 ` [PATCH v2 4/6] [gdb/symtab] Fix data race on bfd_last_cache Tom de Vries
2023-08-02 19:37   ` Tom Tromey
2023-08-03 14:04     ` Tom de Vries
2023-08-02  9:53 ` [PATCH v2 5/6] [gdb/symtab] Fix data race on dwarf2_per_cu_data::{m_header_read_in,is_debug_type} Tom de Vries
2023-08-02 19:39   ` [PATCH v2 5/6] [gdb/symtab] Fix data race on dwarf2_per_cu_data::{m_header_read_in, is_debug_type} Tom Tromey
2023-08-02  9:53 ` [PATCH v2 6/6] [gdb/testsuite] Extend gdb.base/index-cache.exp Tom de Vries
2023-08-02 19:41   ` Tom Tromey
2023-08-02 19:44 ` [PATCH v2 0/6] [gdb/symtab] Fix data-races in gdb.base/index-cache.exp Tom Tromey
2023-08-04  0:14   ` Tom de Vries

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