On 2024-10-13 15:37, Morten Brørup wrote:
From: Mattias Rönnblom [mailto:mattias.ronnb...@ericsson.com]
Sent: Sunday, 13 October 2024 13.57
The macros generating the parallel test for atomic test-and-
[set|clear|flip] functions used a 64-bit reference word when assuring
no neighbouring bits were modified, even when generating code for the
32-bit version of the test.
This issue causes spurious test failures on GCC 12.2.0 (the default
compiler on for example Debian 12 "bookworm"), when optimization level
2 or higher are used.
The test failures do not occur with GCC 11, 12.3 and 13.2.
To the author, this looks like a promotion-related compiler bug in GCC
12.2.
I am curious about the compiler bug...
Did the bug occur when the most significant bit was set, so it sign related?
It seems to happen a lot more often than 1/32 times. Also, all involved
types are unsigned.
If you set the optimization level to "1" (i.e.,
__attribute__((optimize("O"))) on the
test_bit_atomic_parallel_test_and_modify32 function, the test passes on
12.2.0.
Maybe this will reveal something:
TEST_ASSERT(expected_word == word,
"Untouched bits have changed value, %" PRIx ## size
" should be %" PRIx64,
word, expected_word);
Confusingly enough, the failing assertion is the one prior that assertion.
Fixes: 35326b61aecb ("bitops: add atomic bit operations in new API")
Signed-off-by: Mattias Rönnblom <mattias.ronnb...@ericsson.com>
---
I took a deep look into this.
Regardless of what the compiler bug is,
Reviewed-by: Morten Brørup <m...@smartsharesystems.com>
Thanks.
I'm far from sure it's a compiler bug. Just look at the base rate: how
often does the code you just wrote fail because of a bug in your code,
and how often is the root cause to be found in the compiler or the
standard libraries.
