On 11 Feb 2025, at 23:25, Brian Inglis <brian.ing...@systematicsw.ab.ca> wrote: > > On 2025-02-11 13:58, Dimitry Andric wrote: >>> On 11 Feb 2025, at 21:45, Brian Inglis via Cygwin 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)? > > > 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) > > > On Ubuntu 24.04 this program compiles without warnings. > > On which platform - RISCV or SH?
Sorry, I forgot to mention that: just plain old x86_64. I think the Ubuntu package build will have detected TLS support during its configure phase. > > > 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. > > It should as gas supports storage class 'T' for thread, and GCC supports and > uses posix threads. I tried to find Cygwin gcc build logs on https://cygwin.com/cgi-bin2/jobs.cgi?srcpkg=gcc&status=&user=, but that comes up with only "not built" builds, or failed builds. If somebody knows a URL where the configure output can be found, it might shed some more light. > This compiles just fine under Cygwin: > > /* test-thread-storage.c */ > int f(int *np, char *cp) > { > static __thread int n; > static __thread char *p; > int i; > > n = *np; > p = cp; > > for (i = 0; i < n; ++i) > *cp++ = *p++; > > return i; > } > > Cygwin and GCC support POSIX threads, and they are used in many Cygwin > packages, this may just work! > > Cygwin could define its own builtin_thread_pointer() to access its own cygtls > areas from GCC, and if they are defined using storage class 'T', it should > work. > It is not clear if this is just intended as an optimization for a few > embedded targets that have a dedicated pointer register for tls. Yes, that is the RISCV or SH specific method. On x86_64, you access it via the fs register, i.e. gcc (on Linux at least :) compiles: void *p = __builtin_thread_pointer(); to something like: movq %fs:0, %rax movq %rax, -8(%rbp) If somebody knows how to build the Cygwin gcc package from scratch, they could inspect the config.log file, to see what that says about TLS detection. -Dimitry -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
