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
