https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116478
Bug ID: 116478
Summary: x86_64-w64-mingw32-gcc -flto should support and not
warn about __attribute__ ((visibility("default")))
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: public at timruffing dot de
Target Milestone: ---
We got an unexpected "visibility attribute not supported in this configuration"
warning when compiling for mingw with LTO enabled. (Downstream bug:
https://github.com/bitcoin-core/secp256k1/issues/1421)
Here's a minimal test case:
$ cat a.b
__attribute__ ((visibility("default"))) void a(void) {}
$ cat b.c
void a(void);
int main(void) {
a();
}
$ x86_64-w64-mingw32-gcc -flto=2 -flto-partition=max a.c b.c
a.c: In function ‘a’:
a.c:1:55: warning: visibility attribute not supported in this configuration;
ignored [-Wattributes]
1 | __attribute__ ((visibility("default"))) void a(void) {}
|
I believe that the emitted warning reveals a bug. The attribute should be
supported. The manual claims "Default visibility is supported everywhere.", see
https://gcc.gnu.org/onlinedocs/gcc-13.1.0/gcc/Common-Function-Attributes.html .
It may be correct that the attribute has no effect, but then GCC should not
warn about it.
When running without -flto or with -flto-partition=1to1, the warning
disappears. Note that -flto-partition=max is necessary to reproduce this in
this minimal test case. When we encountered the bug in the wild, we got the
warning even with the default -flto-partition=balanced, but like here, it
disappeared with -flto-partition=1to1.
The only other relevant bug I could find is bug 71286, but that seems to be a
different issue.
$ x86_64-w64-mingw32-gcc -v
Using built-in specs.
COLLECT_GCC=x86_64-w64-mingw32-gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-w64-mingw32/13.1.0/lto-wrapper
Target: x86_64-w64-mingw32
Configured with: /build/mingw-w64-gcc/src/gcc/configure --prefix=/usr
--libexecdir=/usr/lib --target=x86_64-w64-mingw32
--with-bugurl=https://bugs.archlinux.org/
--enable-languages=ada,c,c++,fortran,lto,objc,obj-c++ --enable-shared
--enable-static --enable-threads=posix --enable-fully-dynamic-string
--enable-libstdcxx-time=yes --enable-libstdcxx-filesystem-ts=yes
--with-system-zlib --enable-cloog-backend=isl --enable-lto --enable-libgomp
--disable-multilib --enable-checking=release --disable-sjlj-exceptions
--with-dwarf2
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.1.0 (GCC)
