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	Tue, 11 Feb 2025 11:41:28 -0800 (PST)
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Subject:	Re: __builtin_thread_pointer
In-Reply-To:	<9c6a1ccc-d2fb-4aaf-b8c2-29574fa640b4@cornell.edu>
Date:	Tue, 11 Feb 2025 20:41:27 +0100
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References:	<9c6a1ccc-d2fb-4aaf-b8c2-29574fa640b4 AT cornell DOT edu>
To:	Ken Brown <kbrown AT cornell DOT edu>
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From:	Dimitry Andric via Cygwin <cygwin AT cygwin DOT com>
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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.

-Dimitry

> On 11 Feb 2025, at 20:26, Ken Brown via Cygwin <cygwin AT cygwin DOT com> 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.
> 
> Ken
> 
> [242/242] Linking C executable luametatex.exe
> FAILED: luametatex.exe
> : && /usr/bin/gcc.exe -ggdb -O2 -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=3 -fstack-protector-strong --param=ssp-buffer-size=4 -ffile-prefix-map=/home/kbrown/src/cygluametatex/luametatex-2.11.05-1.x86_64/build=/usr/src/debug/luametatex-2.11.05-1 -ffile-prefix-map=/home/kbrown/src/cygluametatex/luametatex-2.11.05-1.x86_64/src/luametatex=/usr/src/debug/luametatex-2.11.05-1 -O2 -g -DNDEBUG -s CMakeFiles/luametatex.dir/source/luametatex.c.o -o luametatex.exe -Wl,--out-implib,libluametatex.dll.a -Wl,--major-image-version,0,--minor-image-version,0  libtex.a  liblua.a libmp.a  libluarest.a  libluasocket.a  libluaoptional.a  libpplib.a libminiz.a  libsoftposit.a  libpotrace.a  -ldl  libmimalloc.a  -lpthread  -lm && /bin/sh CMakeFiles/luametatex.dir/post-build.sh 7847d1a259c666c4
> /usr/lib/gcc/x86_64-pc-cygwin/12/../../../../x86_64-pc-cygwin/bin/ld: libmimalloc.a(alloc.c.o): in function `_mi_prim_thread_id':
> /usr/src/debug/luametatex-2.11.05-1/source/libraries/mimalloc/include/mimalloc/prim.h:251:(.text+0x187): undefined reference to `__builtin_thread_pointer'
> /usr/lib/gcc/x86_64-pc-cygwin/12/../../../../x86_64-pc-cygwin/bin/ld: /usr/src/debug/luametatex-2.11.05-1/source/libraries/mimalloc/include/mimalloc/prim.h:251:(.text+0x437): undefined reference to `__builtin_thread_pointer'
> /usr/lib/gcc/x86_64-pc-cygwin/12/../../../../x86_64-pc-cygwin/bin/ld: /usr/src/debug/luametatex-2.11.05-1/source/libraries/mimalloc/include/mimalloc/prim.h:251:(.text+0x4e7): undefined reference to `__builtin_thread_pointer'
> /usr/lib/gcc/x86_64-pc-cygwin/12/../../../../x86_64-pc-cygwin/bin/ld: libmimalloc.a(alloc.c.o):/usr/src/debug/luametatex-2.11.05-1/source/libraries/mimalloc/src/free.c:340:(.text+0x597): undefined reference to `__builtin_thread_pointer'
> /usr/lib/gcc/x86_64-pc-cygwin/12/../../../../x86_64-pc-cygwin/bin/ld: libmimalloc.a(init.c.o): in function `_mi_prim_thread_id':
> /usr/src/debug/luametatex-2.11.05-1/source/libraries/mimalloc/include/mimalloc/prim.h:251:(.text+0xd1): undefined reference to `__builtin_thread_pointer'
> /usr/lib/gcc/x86_64-pc-cygwin/12/../../../../x86_64-pc-cygwin/bin/ld: libmimalloc.a(init.c.o):/usr/src/debug/luametatex-2.11.05-1/source/libraries/mimalloc/include/mimalloc/prim.h:251: more undefined references to `__builtin_thread_pointer' follow
> collect2: error: ld returned 1 exit status
> 
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