It does not look like it's supported by Cygwin's gcc:
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-cygwin/12/lto-wrapper.exe
Target: x86_64-pc-cygwin
Configured with: /mnt/share/cygpkgs/gcc/gcc.x86_64/src/gcc-12.4.0/configure
--srcdir=/mnt/share/cygpkgs/gcc/gcc.x86_64/src/gcc-12.4.0 --prefix=/usr
--exec-prefix=/usr --localstatedir=/var --sysconfdir=/etc
--docdir=/usr/share/doc/gcc --htmldir=/usr/share/doc/gcc/html -C
--build=x86_64-pc-cygwin --host=x86_64-pc-cygwin --target=x86_64-pc-cygwin
--without-libiconv-prefix --without-libintl-prefix --libexecdir=/usr/lib
--with-gcc-major-version-only --enable-shared --enable-shared-libgcc
--enable-static --enable-version-specific-runtime-libs --enable-bootstrap
--enable-__cxa_atexit --enable-clocale=newlib --with-dwarf2 --with-tune=generic
--enable-languages=ada,c,c++,fortran,lto,objc,obj-c++,jit --enable-graphite
--enable-threads=posix --enable-libatomic --enable-libgomp --enable-libquadmath
--enable-libquadmath-support --disable-libssp --enable-libada --disable-symvers
--disable-multilib --with-gnu-ld --with-gnu-as
--with-cloog-include=/usr/include/cloog-isl --without-libiconv-prefix
--without-libintl-prefix --with-system-zlib --enable-linker-build-id
--with-default-libstdcxx-abi=gcc4-compatible --enable-libstdcxx-filesystem-ts
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.4.0 (GCC)
$ cat test-builtin-thread-pointer.c
void f(void)
{
void *p = __builtin_thread_pointer();
}
$ gcc -c test-builtin-thread-pointer.c
test-builtin-thread-pointer.c: In function ‘f’:
test-builtin-thread-pointer.c:3:13: warning: implicit declaration of function
‘__builtin_thread_pointer’; did you mean ‘__builtin_extend_pointer’?
[-Wimplicit-function-declaration]
3 | void *p = __builtin_thread_pointer();
| ^~~~~~~~~~~~~~~~~~~~~~~~
| __builtin_extend_pointer
test-builtin-thread-pointer.c:3:13: warning: initialization of ‘void *’ from
‘int’ makes pointer from integer without a cast [-Wint-conversion]
On Ubuntu 24.04 this program compiles without warnings.
It looks like the gcc configure script checks for TLS here:
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/configure.ac;h=8fab93c9365496062583c5bd8ace402c8a797817;hb=HEAD#l3846,
by running some code through the assembler. I would guess that doesn't work on
Cygwin.
-Dimitry
> On 11 Feb 2025, at 21:45, Brian Inglis via Cygwin <cygwin@cygwin.com> wrote:
>
>
> On 2025-02-11 12:41, Dimitry Andric via Cygwin wrote:
>>> On 11 Feb 2025, at 20:26, Ken Brown via Cygwin wrote:
>>> Does Cygwin support __builtin_thread_pointer? I'm guessing not, because
>>> I'm getting a link error (undefined reference to
>>> `__builtin_thread_pointer') when I try to build some software that uses
>>> it. Or is there something that would have to be added to the link command
>>> line? The full command line and error message are quoted below, in case
>>> anyone spots something obvious.
>
>> It's a gcc builtin function, not something implemented in an external
>> library. Therefore, there is no linker option that can fix this.
>> Also, as far as I can see from gcc's documentation,
>> __builtin_thread_pointer() is only supported for the RISCV and SH
>> architectures. Then again, gcc's implementation seems to hinge this on
>> whether the platform supports TLS or not.
>> In any case, it is probably better to not use this function if your gcc does
>> not support it.
> Does `info gcc tls` help and do we know if that is supported by our gcc(s)?
>
> --
> Take care. Thanks, Brian Inglis Calgary, Alberta, Canada
>
> La perfection est atteinte Perfection is achieved
> non pas lorsqu'il n'y a plus rien à ajouter not when there is no more to add
> mais lorsqu'il n'y a plus rien à retrancher but when there is no more to cut
> -- Antoine de Saint-Exupéry
>
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