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* [Bug lto/114241] New: False-positive -Wodr warning when using -flto and -fno-semantic-interposition
@ 2024-03-05 15:38 abbeyj+gcc at gmail dot com
2024-03-06 7:46 ` [Bug lto/114241] " rguenth at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: abbeyj+gcc at gmail dot com @ 2024-03-05 15:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114241
Bug ID: 114241
Summary: False-positive -Wodr warning when using -flto and
-fno-semantic-interposition
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: abbeyj+gcc at gmail dot com
Target Milestone: ---
When building the following example, a `-Wodr` warning is shown. I don't think
the code violates the ODR so this warning is unexpected. This reproducer
consists of 3 files.
d.h:
```
class A {
public:
virtual ~A();
virtual void a1();
};
class B : public A {
public:
void a1();
virtual void b1() = 0;
virtual void b2() = 0;
};
class C : public B {
};
class D : public C {
public:
void b1();
void b2();
};
```
foo.cpp:
```
#include "d.h"
void foo() {
D x;
}
```
bar.cpp:
```
#include "d.h"
void B::a1() {
}
void bar() {
D y;
}
```
Build using:
g++ -fPIC -fno-semantic-interposition -flto -c foo.cpp
g++ -fPIC -fno-semantic-interposition -flto -c bar.cpp
g++ -shared foo.o bar.o -o lib.so
Output:
> d.h:14:7: warning: virtual table of type ‘struct C’ violates one definition rule [-Wodr]
> 14 | class C : public B {
> | ^
> d.h:14:7: note: the conflicting type defined in another translation unit has virtual table with more entries
> 14 | class C : public B {
> | ^
The warning message here is not great as it refers to "another translation
unit" but never names either of the two translation units involved. In this
reduced example there are only two translation units but when there are many
translation units involved it is more difficult to figure out where the problem
is coming from.
The bigger issue is that I don't think this warning should have been issued at
all. I can't see any way that the code is violating the ODR.
The earliest version that I've been able to reproduce with is 8.4
Godbolt link: https://godbolt.org/z/ncnqPMdzq
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug lto/114241] False-positive -Wodr warning when using -flto and -fno-semantic-interposition 2024-03-05 15:38 [Bug lto/114241] New: False-positive -Wodr warning when using -flto and -fno-semantic-interposition abbeyj+gcc at gmail dot com @ 2024-03-06 7:46 ` rguenth at gcc dot gnu.org 2024-03-06 9:16 ` hubicka at ucw dot cz 2024-03-06 9:18 ` hubicka at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu.org @ 2024-03-06 7:46 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114241 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |hubicka at gcc dot gnu.org Ever confirmed|0 |1 Known to fail| |13.2.1 Last reconfirmed| |2024-03-06 Status|UNCONFIRMED |NEW --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- Confirmed also with GCC 13. I guess we're optimizing things in a strange (invalid) way before WPA and get confused because of that. Honza? ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug lto/114241] False-positive -Wodr warning when using -flto and -fno-semantic-interposition 2024-03-05 15:38 [Bug lto/114241] New: False-positive -Wodr warning when using -flto and -fno-semantic-interposition abbeyj+gcc at gmail dot com 2024-03-06 7:46 ` [Bug lto/114241] " rguenth at gcc dot gnu.org @ 2024-03-06 9:16 ` hubicka at ucw dot cz 2024-03-06 9:18 ` hubicka at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: hubicka at ucw dot cz @ 2024-03-06 9:16 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114241 --- Comment #2 from Jan Hubicka <hubicka at ucw dot cz> --- This indeed looks like bug caused by fact that the class is keyed into one of the two units. Outputting translation unit names is unfortunately hard, since they are object files and often comming from .a archive where we know only offset, but no original file name or something. I had patch which passed through original filename attached to TRALSATION_UNIT_DECL, but it also had problems, i.e. printing relative filenames from wrong directory. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug lto/114241] False-positive -Wodr warning when using -flto and -fno-semantic-interposition 2024-03-05 15:38 [Bug lto/114241] New: False-positive -Wodr warning when using -flto and -fno-semantic-interposition abbeyj+gcc at gmail dot com 2024-03-06 7:46 ` [Bug lto/114241] " rguenth at gcc dot gnu.org 2024-03-06 9:16 ` hubicka at ucw dot cz @ 2024-03-06 9:18 ` hubicka at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: hubicka at gcc dot gnu.org @ 2024-03-06 9:18 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114241 Jan Hubicka <hubicka at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Assignee|unassigned at gcc dot gnu.org |hubicka at gcc dot gnu.org Status|NEW |ASSIGNED --- Comment #3 from Jan Hubicka <hubicka at gcc dot gnu.org> --- mine. Will debug why the tables diverges. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2024-03-06 9:18 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2024-03-05 15:38 [Bug lto/114241] New: False-positive -Wodr warning when using -flto and -fno-semantic-interposition abbeyj+gcc at gmail dot com 2024-03-06 7:46 ` [Bug lto/114241] " rguenth at gcc dot gnu.org 2024-03-06 9:16 ` hubicka at ucw dot cz 2024-03-06 9:18 ` hubicka at gcc dot gnu.org
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