gccNGPackages: Rework threading model patch based on feedback on IRC (#424918)
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John Ericson
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@ -1,59 +1,50 @@
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From 1eaf7ce77bb4eb73e5565ede220557c2ef0290b0 Mon Sep 17 00:00:00 2001
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From 46280d27a5c96b2efa7a61f49ee8dc14f7e10d0c Mon Sep 17 00:00:00 2001
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From: John Ericson <git@JohnEricson.me>
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Date: Sun, 22 Aug 2021 01:14:22 -0400
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Subject: [PATCH] Allow explicitly specifying the thread model for runtime libs
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Subject: [PATCH] Factor out thread model detection with `GCC_AC_THREAD_MODEL`
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Previously, they always scraped the thread mode from `$CC -v', now, that
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is the default but one may pass `--with-threads=MODEL` to be explicit
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instead.
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This macro deduplicates the
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One use-case is bootstraping with a shorter critical path. The
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traditionally route was to build an entire "static stage" GCC, build
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libc, and then build GCC again supporting dynamic linking,
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multithreading, etc. But this is wasteful in that GCC itself is built
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twice.
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$CC -v 2>&1 | sed -n 's/^Thread model: //p'
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With this change, rather than having to mess with spec files we can just
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configure the runtime libraries the way we want directly. In turn, that
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opens to just building libgcc twice rather than all of GCC.
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check that was occurring in various runtime libs.
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Frankly, specs were always a rather indirect approach to coordinate this
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during GCC's bootstrap, since GCC itself really doesn't care what the
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threading model is, just that the runtime libraries agree among
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themselves. Relying on a hard-coded spec for this also keeps us one step
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further from the long-term goal of multi-target GCC, for what it's
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worth.
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Additionally, as a bit of an Easter egg, this also allows overriding
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what the compiler would return by setting the
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`gcc_cv_target_thread_file` cache variable first. I admit that it is in
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fact this Easter egg that led me to write the patch. The use-case for it
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is for making multilib builds where the library sets do not all share
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the same thread model easier. See also `THREAD_MODEL_SPEC` for more
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about the varying thread models use-case.
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For the record, "single stage" builds of GCC have some precedent in
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downstream packaging, for example with [1]. That one, as far as I can
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tell, builds libgcc once, but with the headers of the libc
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implementation provided and then cyclic linking down later. They are
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both fine approaches, but I don't think one should have to be forced
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into cyclic dependencies if they don't want to. That opens the door to
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non-terminating programs due to, e.g., atomics used in a threads
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implementation being lowered to threads absent hardware support.
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Arguably one could could try to define on `THREAD_MODEL_SPEC` on more
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platforms (besides e.g. AIX) but the ramifications of this are a bit
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unclear. Setting `gcc_cv_target_thread_file` directly is a "low tech"
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solution that will work for now for sure. Of course, since setting a
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cache variable like this a hacky trick, I will not expect this to be at
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all stable/guaranteed to work, going forward.
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Finally, I understand that such custom bootstrapping is not officially
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supported. I don't mean to imply it should be --- a lot more cleanup
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work to the build system would be necessary before supporting it
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wouldn't be a huge additional maintainer burden --- I just hope to add a
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reasonable knob for those comfortable with doing unsupported things
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already.
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Thanks to Arsen who on IRC discussed these things with me, including in
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particular making it a cache var not `--with-model` flag, to not
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prematurely foster expectations that this is stable.
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[1]: https://github.com/richfelker/musl-cross-make
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Suggested-by: Arsen Arsenović <arsen@aarsen.me>
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---
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config/gthr.m4 | 32 ++++++++++++++++++++++++++++++++
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config/gthr.m4 | 23 +++++++++++++++++++++++
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libatomic/configure.ac | 4 +---
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libgcc/configure.ac | 4 +---
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libphobos/m4/druntime/os.m4 | 2 +-
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libstdc++-v3/acinclude.m4 | 8 +++-----
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5 files changed, 38 insertions(+), 12 deletions(-)
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5 files changed, 29 insertions(+), 12 deletions(-)
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diff --git a/config/gthr.m4 b/config/gthr.m4
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index 11996247f15..7aed5d3df0d 100644
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index 11996247f15..e8fac4a5721 100644
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--- a/config/gthr.m4
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+++ b/config/gthr.m4
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@@ -5,6 +5,35 @@ dnl Public License, this file may be distributed as part of a program
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@@ -5,6 +5,26 @@ dnl Public License, this file may be distributed as part of a program
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dnl that contains a configuration script generated by Autoconf, under
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dnl the same distribution terms as the rest of that program.
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@ -62,34 +53,25 @@ index 11996247f15..7aed5d3df0d 100644
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+dnl usage: GCC_AC_THREAD_MODEL
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+AC_DEFUN([GCC_AC_THREAD_MODEL],
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+[
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+# With threads
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+# Specify the threading model for this GCC runtime library
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+# Pass with no value to take from compiler's metadata
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+# Pass with a value to specify a thread package
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+# 'single' means single threaded -- without threads.
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+AC_ARG_WITH(threads,
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+[AS_HELP_STRING([[--with-threads=MODEL]],
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+ [specify thread model for this GCC
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+ runtime library])],,
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+[with_threads=''])
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+
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+if test x"$with_threads" = x'yes'; then
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+ AC_MSG_ERROR([Cannot pass bare --with-threads, must pass explicit --with-threads=MODEL])
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+elif test x"$with_threads" = x'no'; then
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+ target_thread_file=single
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+elif test x"$with_threads" = x''; then
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+ AC_MSG_CHECKING([for thread model used by GCC])
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+ target_thread_file=`$CC -v 2>&1 | sed -n 's/^Thread model: //p'`
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+ AC_MSG_RESULT([$target_thread_file])
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+else
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+ target_thread_file=$with_threads
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+fi
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+AC_CACHE_CHECK([for the threading model used by GCC], [gcc_cv_target_thread_file], [
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+ # Set new cache variable
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+ gcc_cv_target_thread_file=`$CC -v 2>&1 | sed -n 's/^Thread model: //p'`
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+])
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+# Set variable name (not prefixed enough to be a good cache variable
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+# name) traditionally used for this purpose, to avoid having to change
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+# a bunch of configure scripts.
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+target_thread_file="$gcc_cv_target_thread_file"
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+])
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+
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+
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dnl Define header location by thread model
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dnl usage: GCC_AC_THREAD_HEADER([thread_model])
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@@ -23,6 +52,9 @@ case $1 in
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@@ -23,6 +43,9 @@ case $1 in
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vxworks) thread_header=config/gthr-vxworks.h ;;
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win32) thread_header=config/i386/gthr-win32.h ;;
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mcf) thread_header=config/i386/gthr-mcf.h ;;
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@ -100,7 +82,7 @@ index 11996247f15..7aed5d3df0d 100644
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AC_SUBST(thread_header)
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])
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diff --git a/libatomic/configure.ac b/libatomic/configure.ac
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index 85824fa7614..691f4948f6c 100644
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index aafae71028d..a1aa3bdf69f 100644
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--- a/libatomic/configure.ac
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+++ b/libatomic/configure.ac
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@@ -162,9 +162,7 @@ libtool_VERSION=3:0:2
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@ -115,7 +97,7 @@ index 85824fa7614..691f4948f6c 100644
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case "$target" in
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*aarch64*)
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diff --git a/libgcc/configure.ac b/libgcc/configure.ac
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index 4e8c036990f..acf54e24c79 100644
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index 85e4f1bc48b..d44493f9653 100644
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--- a/libgcc/configure.ac
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+++ b/libgcc/configure.ac
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@@ -305,9 +305,7 @@ AC_SUBST([use_tm_clone_registry])
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@ -130,7 +112,7 @@ index 4e8c036990f..acf54e24c79 100644
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# Check for assembler CFI support.
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AC_CACHE_CHECK([whether assembler supports CFI directives], [libgcc_cv_cfi],
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diff --git a/libphobos/m4/druntime/os.m4 b/libphobos/m4/druntime/os.m4
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index 15cde3b04b8..28bd4d3d2bd 100644
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index ef8ca434407..7bb91362dbe 100644
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--- a/libphobos/m4/druntime/os.m4
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+++ b/libphobos/m4/druntime/os.m4
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@@ -32,7 +32,7 @@ case $1 in
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@ -143,10 +125,10 @@ index 15cde3b04b8..28bd4d3d2bd 100644
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AC_SUBST(DCFG_THREAD_MODEL)
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])
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diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
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index 51a08bcc8b1..71697f59d6d 100644
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index a0094c2dd95..66fc3abe4fd 100644
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--- a/libstdc++-v3/acinclude.m4
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+++ b/libstdc++-v3/acinclude.m4
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@@ -4342,9 +4342,7 @@ dnl Substs:
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@@ -4345,9 +4345,7 @@ dnl Substs:
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dnl thread_header
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dnl
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AC_DEFUN([GLIBCXX_ENABLE_THREADS], [
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@ -157,7 +139,7 @@ index 51a08bcc8b1..71697f59d6d 100644
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GCC_AC_THREAD_HEADER([$target_thread_file])
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])
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@@ -4354,7 +4352,8 @@ dnl Check if gthread implementation defines the types and functions
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@@ -4357,7 +4355,8 @@ dnl Check if gthread implementation defines the types and functions
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dnl required by the c++0x thread library. Conforming gthread
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dnl implementations can define __GTHREADS_CXX0X to enable use with c++0x.
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dnl
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@ -167,7 +149,7 @@ index 51a08bcc8b1..71697f59d6d 100644
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dnl
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AC_DEFUN([GLIBCXX_CHECK_GTHREADS], [
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GLIBCXX_ENABLE(libstdcxx-threads,auto,,[enable C++11 threads support])
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@@ -4369,7 +4368,6 @@ AC_DEFUN([GLIBCXX_CHECK_GTHREADS], [
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@@ -4372,7 +4371,6 @@ AC_DEFUN([GLIBCXX_CHECK_GTHREADS], [
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CXXFLAGS="$CXXFLAGS -fno-exceptions \
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-I${toplevel_srcdir}/libgcc -I${toplevel_builddir}/libgcc"
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@ -176,5 +158,5 @@ index 51a08bcc8b1..71697f59d6d 100644
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posix)
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CXXFLAGS="$CXXFLAGS -DSUPPORTS_WEAK -DGTHREAD_USE_WEAK -D_PTHREADS"
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--
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2.44.1
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2.47.2
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@ -51,21 +51,10 @@ stdenv.mkDerivation (finalAttrs: {
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];
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patches = [
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# Submitted:
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# - https://gcc.gnu.org/pipermail/gcc-patches/2021-August/577639.html
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# - https://gcc.gnu.org/pipermail/gcc-patches/2021-August/577640.html
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# - https://gcc.gnu.org/pipermail/gcc-patches/2021-August/577638.html
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#
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# In Git: https://github.com/Ericson2314/gcc/tree/prog-target-15
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(getVersionFile "gcc/0001-find_a_program-First-search-with-machine-prefix.patch")
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(getVersionFile "gcc/0002-driver-for_each_pass-Pass-to-callback-whether-dir-is.patch")
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(getVersionFile "gcc/0003-find_a_program-Only-search-for-prefixed-paths-in-und.patch")
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# Submitted: https://inbox.sourceware.org/gcc-patches/20210818203840.1550133-1-John.Ericson@Obsidian.Systems/T/#t
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# In Git: https://github.com/Ericson2314/gcc/tree/libgcc-custom-threading-model-15
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(getVersionFile "gcc/custom-threading-model.patch")
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# TODO: fix up and send to upstream
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(getVersionFile "gcc/fix-collect2-paths.diff")
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];
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@ -169,7 +169,7 @@ stdenv.mkDerivation (finalAttrs: {
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configureFlags = [
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"--disable-dependency-tracking"
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"--with-threads=single"
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"gcc_cv_target_thread_file=single"
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# $CC cannot link binaries, let alone run then
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"cross_compiling=true"
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# Do not have dynamic linker without libc
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@ -158,7 +158,7 @@ stdenv.mkDerivation (finalAttrs: {
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configureFlags = [
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"--disable-dependency-tracking"
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"--with-threads=single"
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"gcc_cv_target_thread_file=single"
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# $CC cannot link binaries, let alone run then
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"cross_compiling=true"
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];
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@ -53,7 +53,7 @@ stdenv.mkDerivation (finalAttrs: {
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configureFlags = [
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"--disable-dependency-tracking"
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"--with-toolexeclibdir=${builtins.placeholder "out"}/lib"
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"--with-threads=posix"
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"gcc_cv_target_thread_file=posix"
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"cross_compiling=true"
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"--disable-multilib"
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@ -1,10 +1,18 @@
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{
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# TODO: fix up and send to upstream
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"gcc/fix-collect2-paths.diff" = [
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{
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after = "15";
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path = ../15;
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}
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];
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# Submitted (001--003):
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# - https://gcc.gnu.org/pipermail/gcc-patches/2021-August/577639.html
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# - https://gcc.gnu.org/pipermail/gcc-patches/2021-August/577640.html
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# - https://gcc.gnu.org/pipermail/gcc-patches/2021-August/577638.html
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#
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# In Git: https://github.com/Ericson2314/gcc/tree/prog-target-15
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"gcc/0001-find_a_program-First-search-with-machine-prefix.patch" = [
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{
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after = "15";
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@ -23,6 +31,9 @@
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path = ../15;
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}
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];
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# Submitted: https://gcc.gnu.org/pipermail/gcc-patches/2025-July/689429.html
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# In Git: https://github.com/Ericson2314/gcc/tree/libgcc-custom-threading-model-15
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"gcc/custom-threading-model.patch" = [
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{
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after = "15";
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