https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85580
Bug ID: 85580
Summary: "conflicting C language linkage declaration" warning
for variables with identical names in `extern "C"`
functions
Product: gcc
Version: 8.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: freddie_chopin at op dot pl
Target Milestone: ---
Here's a minimal test case executed with 8.0.1-RC-20180427 (compiled for
arm-none-eabi target, but I think the problem is not target-specific):
-- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 --
$ cat test.cpp
extern "C"
{
void f1()
{
union some_type{
char a[2];
int b;
} variable;
}
void f2()
{
union some_type{
char a[2];
int b;
} variable;
}
}
$ arm-none-eabi-gcc test.cpp -c
test.cpp: In function 'void f2()':
test.cpp:17:5: warning: conflicting C language linkage declaration
'f2()::some_type variable'
} variable;
^~~~~~~~
test.cpp:9:5: note: previous declaration 'f1()::some_type variable'
} variable;
^~~~~~~~
$ arm-none-eabi-gcc --version
arm-none-eabi-gcc (bleeding-edge-toolchain) 8.0.1 20180427 (prerelease)
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is
NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.
-- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 --
For the problem to appear:
- functions with the types and variables have to be extern "C"
- the file must be C++
- there has to be both a type and a variable
- the variables must have identical names
The problem was spotted with ARM CMSIS headers, where similar pattern exists:
https://github.com/ARM-software/CMSIS_5/blob/develop/CMSIS/Core/Include/cmsis_gcc.h#L1929
Related discussion on mailing list:
https://gcc.gnu.org/ml/gcc/2018-04/msg00191.html
