Hello, this 4-year-old patch of mine was never reviewed. Per https://github.com/NixOS/nixpkgs/pull/414299, we in a package set / distro, Nixpkgs/NixOS, just began (albeit on an experimental basis) packaging GCC with this patch (among others) applied. It would thus be nice to get it applied upstream --- if changes are needed, of course we can make them and resubmit.
(The is also visible at https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/compilers/gcc/ng/15/gcc/custom-threading-model.patch.) This is I think the conceptually simplest patch/series of the ones we have in there, so a good one to start with. (I think it would be unnecessary complicated to discuss them all at once.) Thanks in advance, John On Wed, Aug 18, 2021, at 4:38 PM, John Ericson wrote: > From: John Ericson <g...@johnericson.me> > > Previously, they always scraped the thread mode from `$CC -v', now, that > is the default but one may pass `--with-threads=MODEL` to be explicit > instead. > > One use-case is bootstraping with a shorter critical path. The > traditionally route was to build an entire "static stage" GCC, build > libc, and then build GCC again supporting dynamic linking, > multithreading, etc. But this is wasteful in that GCC itself is built > twice. > > With this change, rather than having to mess with spec files we can just > configure the runtime libraries the way we want directly. In turn, that > opens to just building libgcc twice rather than all of GCC. > > Frankly, specs were always a rather indirect approach to coordinate this > during GCC's bootstrap, since GCC itself really doesn't care what the > threading model is, just that the runtime libraries agree among > themselves. Relying on a hard-coded spec for this also keeps us one step > further from the long-term goal of multi-target GCC, for what it's > worth. > > For the record, "single stage" builds of GCC have some precedent in > downstream packaging, for example with [1]. That one, as far as I can > tell, builds libgcc once, but with the headers of the libc > implementation provided and then cyclic linking down later. They are > both fine approaches, but I don't think one should have to be forced > into cyclic dependencies if they don't want to. That opens the door to > non-terminating programs due to, e.g., atomics used in a threads > implementation being lowered to threads absent hardware support. > > Finally, I understand that such custom bootstrapping is not officially > supported. I don't mean to imply it should be --- a lot more cleanup > work to the build system would be necessary before supporting it > wouldn't be a huge additional maintainer burden --- I just hope to add a > reasonable knob for those comfortable with doing unsupported things > already. > > [1]: https://github.com/richfelker/musl-cross-make > --- > config/gthr.m4 | 32 ++++++++++++++++++++++++++++++++ > libatomic/configure.ac | 4 +--- > libgcc/configure.ac | 4 +--- > libphobos/m4/druntime/os.m4 | 2 +- > libstdc++-v3/acinclude.m4 | 8 +++----- > 5 files changed, 38 insertions(+), 12 deletions(-) > > diff --git a/config/gthr.m4 b/config/gthr.m4 > index 4b937306ad0..c585b618e40 100644 > --- a/config/gthr.m4 > +++ b/config/gthr.m4 > @@ -5,6 +5,35 @@ dnl Public License, this file may be distributed as part of > a program > dnl that contains a configuration script generated by Autoconf, under > dnl the same distribution terms as the rest of that program. > > +dnl Define thread model > + > +dnl usage: GCC_AC_THREAD_MODEL > +AC_DEFUN([GCC_AC_THREAD_MODEL], > +[ > +# With threads > +# Pass with no value to take from compiler's metadata > +# Pass with a value to specify a thread package > +# 'single' means single threaded -- without threads. > +AC_ARG_WITH(threads, > +[AS_HELP_STRING([[--with-threads=MODEL]], > + [specify thread model for this GCC > + runtime library])],, > +[with_threads='']) > + > +if test x"$with_threads" = x'yes'; then > + AC_MSG_ERROR([Cannot pass bare --with-threads, must pass explicit > --with-threads=MODEL]) > +elif test x"$with_threads" = x'no'; then > + target_thread_file=single > +elif test x"$with_threads" = ''; then > + AC_MSG_CHECKING([for thread model used by GCC]) > + target_thread_file=`$CC -v 2>&1 | sed -n 's/^Thread model: //p'` > + AC_MSG_RESULT([$target_thread_file]) > +else > + target_thread_file=$with_threads > +fi > +]) > + > + > dnl Define header location by thread model > > dnl usage: GCC_AC_THREAD_HEADER([thread_model]) > @@ -22,6 +51,9 @@ case $1 in > tpf) thread_header=config/s390/gthr-tpf.h ;; > vxworks) thread_header=config/gthr-vxworks.h ;; > win32) thread_header=config/i386/gthr-win32.h ;; > + *) > + AC_MSG_ERROR([No known header for threading model '$1'.]) > + ;; > esac > AC_SUBST(thread_header) > ]) > diff --git a/libatomic/configure.ac b/libatomic/configure.ac > index 2a371870c2f..42d2016b7a2 100644 > --- a/libatomic/configure.ac > +++ b/libatomic/configure.ac > @@ -161,9 +161,7 @@ libtool_VERSION=3:0:2 > AC_SUBST(libtool_VERSION) > > # Check for used threading-model > -AC_MSG_CHECKING([for thread model used by GCC]) > -target_thread_file=`$CC -v 2>&1 | sed -n 's/^Thread model: //p'` > -AC_MSG_RESULT([$target_thread_file]) > +GCC_AC_THREAD_MODEL > > case "$target" in > *aarch64*) > diff --git a/libgcc/configure.ac b/libgcc/configure.ac > index 13a80b2551b..1209a0986e0 100644 > --- a/libgcc/configure.ac > +++ b/libgcc/configure.ac > @@ -298,9 +298,7 @@ AC_SUBST([use_tm_clone_registry]) > > AC_LIB_PROG_LD_GNU > > -AC_MSG_CHECKING([for thread model used by GCC]) > -target_thread_file=`$CC -v 2>&1 | sed -n 's/^Thread model: //p'` > -AC_MSG_RESULT([$target_thread_file]) > +GCC_AC_THREAD_MODEL > > # Check for assembler CFI support. > AC_CACHE_CHECK([whether assembler supports CFI directives], [libgcc_cv_cfi], > diff --git a/libphobos/m4/druntime/os.m4 b/libphobos/m4/druntime/os.m4 > index 351558dbcda..2b44fbca8fc 100644 > --- a/libphobos/m4/druntime/os.m4 > +++ b/libphobos/m4/druntime/os.m4 > @@ -32,7 +32,7 @@ case $1 in > # TODO: These targets need porting. > dce|mipssde|rtems|tpf|vxworks) > DCFG_THREAD_MODEL="Single" ;; > - *) as_fn_error "Thread implementation '$1' not recognised" "$LINENO" > 5 ;; > + *) AC_MSG_ERROR([Thread implementation '$1' not recognised]) ;; > esac > AC_SUBST(DCFG_THREAD_MODEL) > ]) > diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4 > index 90ecc4a87a2..83204176c05 100644 > --- a/libstdc++-v3/acinclude.m4 > +++ b/libstdc++-v3/acinclude.m4 > @@ -3910,9 +3910,7 @@ dnl Substs: > dnl thread_header > dnl > AC_DEFUN([GLIBCXX_ENABLE_THREADS], [ > - AC_MSG_CHECKING([for thread model used by GCC]) > - target_thread_file=`$CXX -v 2>&1 | sed -n 's/^Thread model: //p'` > - AC_MSG_RESULT([$target_thread_file]) > + GCC_AC_THREAD_MODEL > GCC_AC_THREAD_HEADER([$target_thread_file]) > ]) > > @@ -3922,7 +3920,8 @@ dnl Check if gthread implementation defines the types > and functions > dnl required by the c++0x thread library. Conforming gthread > dnl implementations can define __GTHREADS_CXX0X to enable use with c++0x. > dnl > -dnl GLIBCXX_ENABLE_SYMVERS must be done before this. > +dnl GLIBCXX_ENABLE_SYMVERS and GLIBCXX_ENABLE_THREADS must be done > +dnl before this. > dnl > AC_DEFUN([GLIBCXX_CHECK_GTHREADS], [ > GLIBCXX_ENABLE(libstdcxx-threads,auto,,[enable C++11 threads support]) > @@ -3937,7 +3936,6 @@ AC_DEFUN([GLIBCXX_CHECK_GTHREADS], [ > CXXFLAGS="$CXXFLAGS -fno-exceptions \ > -I${toplevel_srcdir}/libgcc -I${toplevel_builddir}/libgcc" > > - target_thread_file=`$CXX -v 2>&1 | sed -n 's/^Thread model: //p'` > case $target_thread_file in > posix) > CXXFLAGS="$CXXFLAGS -DSUPPORTS_WEAK -DGTHREAD_USE_WEAK -D_PTHREADS" > -- > 2.31.1 > >
