From: "gprocida at google dot com" <sourceware-bugzilla@sourceware.org>
To: libabigail@sourceware.org
Subject: [Bug default/28939] New: diff output is sensitive to implementation of std::sort
Date: Thu, 03 Mar 2022 14:29:02 +0000 [thread overview]
Message-ID: <bug-28939-9487@http.sourceware.org/bugzilla/> (raw)
https://sourceware.org/bugzilla/show_bug.cgi?id=28939
Bug ID: 28939
Summary: diff output is sensitive to implementation of
std::sort
Product: libabigail
Version: unspecified
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: default
Assignee: dodji at redhat dot com
Reporter: gprocida at google dot com
CC: libabigail at sourceware dot org
Target Milestone: ---
I received a notification that at least one abidiff is sensitive to the
particular implementation of std::sort.
std::sort gives no guarantees as to the relative ordering of elements that
compare equal (!(a < b) && !(b < a)).
The comparison functor diff_less_than_functor only examines the first diff
subjects and in general there is no guarantee that sorting distinct diffs will
yield a consistent ordering.
The particular test case that was reported was this one:
--- tests/data/test-abidiff-exit/test-member-size-report0.txt 2022-01-30
18:02:19.412941913 -0800
+++ tests/output/test-abidiff-exit/test-member-size-report0.txt 2022-01-30
18:02:20.180941537 -0800
@@ -4,16 +4,15 @@
2 functions with some indirect sub-type change:
[C] 'function void reg1(S*, T*, T*)' at test-member-size-v1.cc:26:1 has some
indirect sub-type changes:
- parameter 1 of type 'S*' has sub-type changes:
- in pointed to type 'struct S' at test-member-size-v1.cc:3:1:
- type size changed from 128 to 192 (in bits)
- 1 data member insertion:
- 'int y', at offset 128 (in bits) at test-member-size-v1.cc:6:1
- no data member change (1 filtered);
- parameter 2 of type 'T*' has sub-type changes:
+ parameter 3 of type 'T*' has sub-type changes:
in pointed to type 'struct T' at test-member-size-v1.cc:14:1:
type size changed from 192 to 256 (in bits)
- 1 data member changes (1 filtered):
+ 2 data member changes:
+ type of 'S s' changed:
+ type size changed from 128 to 192 (in bits)
+ 1 data member insertion:
+ 'int y', at offset 128 (in bits) at test-member-size-v1.cc:6:1
+ no data member change (1 filtered);
'int a' offset changed from 128 to 192 (in bits) (by +64 bits)
In general, dependence on the implementation of std::sort can be discovered by
randomising the input order before sorting.
There are two approaches to improving order stability:
1. increase the discrimination of the comparison function
2. use stable_sort
I'll try to post a patch that does both.
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next reply other threads:[~2022-03-03 14:29 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-03 14:29 gprocida at google dot com [this message]
2022-03-03 14:57 ` [Bug default/28939] " gprocida at google dot com
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