Add experimental aarch64-pc-msys support

PORTING_ARM64_CLANG.md

@@ -0,0 +1,119 @@
+# MSYS2 runtime ARM64/Clang port attempt
+
+Target: native Windows ARM64 (`aarch64-pc-msys`) using LLVM-MinGW Clang.
+
+The ARM64 runtime foundation comes from the
+[Windows-on-ARM-Experiments](https://github.com/Windows-on-ARM-Experiments)
+Cygwin work. This branch adapts that direction to the MSYS2/Clang build and
+records reproducible validation in a Windows 11 ARM64 QEMU VM. Its primary
+result is the tested QEMU path, not an independently completed runtime port.
+
+## Bootstrap order
+
+1. Build GNU binutils for `aarch64-w64-mingw32`.
+2. Use Clang as the C/C++ frontend with the ARM64 PE/COFF target.
+3. Build newlib plus the MSYS/Cygwin public headers and w32api surface.
+4. Build and link `msys-2.0.dll`.
+5. Build the shell and core packages against that runtime.
+
+GNU binutils was cloned separately from sourceware because the MSYS2 runtime
+repository does not carry the `bfd`, `gas`, `ld`, or `binutils` source trees.
+Upstream binutils commit `ebf22fc26326ad138bea9dee536cf081e46dd6e1`
+built successfully on macOS for `aarch64-w64-mingw32`.  The resulting GNU ld
+2.46.50 exposes both `aarch64pe` and `arm64pe` emulations, along with GAS,
+`dlltool`, `windres`, `objcopy`, `objdump`, `nm`, and archive tools.
+
+## Baseline
+
+- Upstream commit: `01d6c708f9221334d18ab332621b6d87eb12d37e`
+- The top-level configure accepts `aarch64-pc-msys` when Clang is supplied as
+  `CC_FOR_TARGET`.
+- ARM64 newlib compiles substantially before the first failure.
+
+## First failure
+
+LLVM-MinGW's compiler wrapper injects its UCRT sysroot while the runtime build
+also injects newlib.  The two header worlds disagree about `ssize_t` on LLP64:
+
+```text
+LLVM-MinGW corecrt.h: typedef __int64 ssize_t;
+newlib sys/types.h:  typedef long _ssize_t;
+```
+
+The port toolchain wrapper uses LLVM's ARM64 PE/COFF backend and builtin headers
+but suppresses the UCRT include tree with `-nostdinc`.
+
+## Second failure
+
+The generic LLVM-MinGW ARM64 target follows the Windows ABI and uses 64-bit
+`long double`.  That bootstrap exposed a newlib source-selection bug: after
+detecting `_LDBL_EQ_DBL`, newlib still selected `libm/ld` sources requiring
+an extended `fpmath.h` layout.  The added Automake conditional skips those
+sources whenever the compiler reports identical double representations.
+
+The final `CygwinARM64TargetInfo` deliberately exposes an LP64 Unix ABI with
+IEEE binary128 `long double`; it therefore selects AArch64's `libm/ld128`
+sources.  Compiler, newlib, and support libraries must agree on that choice.
+
+## Explicit upstream architecture gates found
+
+- `winsup/configure.ac` rejected every target except `x86_64`.
+- MinGW helper discovery required GCC-named executables.
+- `winsup/cygwin/cygwin.sc.in` only emitted `pei-x86-64`.
+- Runtime startup, context switching, TLS, exception unwinding, fork, and math
+  still contain numerous x86-64 assembly and register-layout assumptions.
+
+This is an early bring-up branch, not yet a production runtime.
+
+## Third failure
+
+After excluding UCRT, newlib reaches its MSYS/Windows allocator and requires
+`windows.h`.  The wrapper therefore searches LLVM-MinGW's Win32 headers with
+`-idirafter` (after newlib), while defining the UCRT compatibility guards for
+the ABI types already owned by newlib.
+
+Generic LLVM-MinGW also defines the build as ordinary Win32, selecting
+newlib's obsolete 32-bit `VirtualAlloc`-based `wsbrk`.  The port driver defines
+the Cygwin/MSYS target macros so newlib follows the runtime-provided `sbrk`
+path, matching what an eventual `aarch64-pc-msys-clang` target should do
+natively inside Clang.
+
+Defining the runtime identity also makes newlib include `cygwin/config.h`, so
+the bootstrap driver stages `winsup/cygwin/include` before the full winsup
+install exists.
+
+## First runtime architecture primitive
+
+`cygwin/config.h::__getreent()` obtains the per-thread newlib state through
+the Windows TEB.  x86-64 reads `GS:8`; Windows ARM64 reserves `x18` as the TEB
+pointer, so the ARM64 implementation loads the corresponding pointer from
+`x18 + 8` before applying `__CYGTLS_PADSIZE__`.
+
+The next newlib dependency is the public signal/ucontext ABI.  The port adds an
+ARM64 `__mcontext` matching Windows `ARM64_NT_CONTEXT` (X0-X30, SP, PC, NEON,
+FP status/control, breakpoint and watchpoint registers), followed by Cygwin's
+`oldmask` and `cr2` extension fields.
+
+## Current result
+
+The paired LLVM patch provides an LP64 `CygwinARM64TargetInfo`, and the patched
+newlib and winsup sources produce a native ARM64 `msys-2.0.dll`.  The tested
+runtime loads natively and runs Bash 5.3, fork, pipe-fork, command substitution,
+subshell status, and external-process probes in Windows 11 ARM64 under QEMU.
+
+This remains bring-up validation rather than production support.  Long Bash
+argument vectors can be corrupted, `/tmp` setup emits a warning, transient
+child-start faults are retried, and the full runtime testsuite is not green.
+The reproducibility bundle records exact hashes and observed probe output.
+
+## MSYS newlib target recognition
+
+`newlib/configure.host` carried Cygwin-specific runtime flags only for
+`*-*-cygwin*`; the `aarch64-pc-msys` target therefore tried to compile its own
+allocator and syscalls.  MSYS uses the same integration contract, so the MSYS
+patterns now receive `MALLOC_PROVIDED`, `GETREENT_PROVIDED`, signal/syscall
+flags, POSIX/XDR directories, and the winsup include staging.
+
+Clang's resource headers are placed with `-idirafter`.  Its builtin `float.h`
+uses `include_next` and otherwise reaches LLVM-MinGW's UCRT `float.h` ahead of
+newlib, causing macro and ABI collisions.

compile

@@ -1,9 +1,9 @@
 #! /bin/sh
 # Wrapper for compilers which do not understand '-c -o'.
 
-scriptversion=2012-10-14.11; # UTC
+scriptversion=2025-06-18.21; # UTC
 
-# Copyright (C) 1999-2014 Free Software Foundation, Inc.
+# Copyright (C) 1999-2025 Free Software Foundation, Inc.
 # Written by Tom Tromey <tromey@cygnus.com>.
 #
 # This program is free software; you can redistribute it and/or modify
@@ -17,7 +17,7 @@ scriptversion=2012-10-14.11; # UTC
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 # As a special exception to the GNU General Public License, if you
 # distribute this file as part of a program that contains a
@@ -37,11 +37,11 @@ IFS=" ""	$nl"
 
 file_conv=
 
-# func_file_conv build_file lazy
+# func_file_conv build_file unneeded_conversions
 # Convert a $build file to $host form and store it in $file
 # Currently only supports Windows hosts. If the determined conversion
-# type is listed in (the comma separated) LAZY, no conversion will
-# take place.
+# type is listed in (the comma separated) UNNEEDED_CONVERSIONS, no
+# conversion will take place.
 func_file_conv ()
 {
   file=$1
@@ -51,9 +51,20 @@ func_file_conv ()
 	# lazily determine how to convert abs files
 	case `uname -s` in
 	  MINGW*)
-	    file_conv=mingw
+	    if test -n "$MSYSTEM" && (cygpath --version) >/dev/null 2>&1; then
+	      # MSYS2 environment.
+	      file_conv=cygwin
+	    else
+	      # Original MinGW environment.
+	      file_conv=mingw
+	    fi
+	    ;;
+	  MSYS*)
+	    # Old MSYS environment, or MSYS2 with 32-bit MSYS2 shell.
+	    file_conv=cygwin
 	    ;;
 	  CYGWIN*)
+	    # Cygwin environment.
 	    file_conv=cygwin
 	    ;;
 	  *)
@@ -63,12 +74,14 @@ func_file_conv ()
       fi
       case $file_conv/,$2, in
 	*,$file_conv,*)
+	  # This is the optimization mentioned above:
+	  # If UNNEEDED_CONVERSIONS contains $file_conv, don't convert.
 	  ;;
 	mingw/*)
 	  file=`cmd //C echo "$file " | sed -e 's/"\(.*\) " *$/\1/'`
 	  ;;
 	cygwin/*)
-	  file=`cygpath -m "$file" || echo "$file"`
+	  file=`cygpath -w "$file" || echo "$file"`
 	  ;;
 	wine/*)
 	  file=`winepath -w "$file" || echo "$file"`
@@ -143,7 +156,7 @@ func_cl_wrapper ()
 	  # configure might choose to run compile as 'compile cc -o foo foo.c'.
 	  eat=1
 	  case $2 in
-	    *.o | *.[oO][bB][jJ])
+	    *.o | *.lo | *.[oO][bB][jJ])
 	      func_file_conv "$2"
 	      set x "$@" -Fo"$file"
 	      shift
@@ -248,14 +261,18 @@ If you are trying to build a whole package this is not the
 right script to run: please start by reading the file 'INSTALL'.
 
 Report bugs to <bug-automake@gnu.org>.
+GNU Automake home page: <https://www.gnu.org/software/automake/>.
+General help using GNU software: <https://www.gnu.org/gethelp/>.
 EOF
     exit $?
     ;;
   -v | --v*)
-    echo "compile $scriptversion"
+    echo "compile (GNU Automake) $scriptversion"
     exit $?
     ;;
-  cl | *[/\\]cl | cl.exe | *[/\\]cl.exe )
+  cl | *[/\\]cl | cl.exe | *[/\\]cl.exe | \
+  clang-cl | *[/\\]clang-cl | clang-cl.exe | *[/\\]clang-cl.exe | \
+  icl | *[/\\]icl | icl.exe | *[/\\]icl.exe )
     func_cl_wrapper "$@"      # Doesn't return...
     ;;
 esac
@@ -339,9 +356,9 @@ exit $ret
 # Local Variables:
 # mode: shell-script
 # sh-indentation: 2
-# eval: (add-hook 'write-file-hooks 'time-stamp)
+# eval: (add-hook 'before-save-hook 'time-stamp nil t)
 # time-stamp-start: "scriptversion="
-# time-stamp-format: "%:y-%02m-%02d.%02H"
-# time-stamp-time-zone: "UTC"
+# time-stamp-format: "%Y-%02m-%02d.%02H"
+# time-stamp-time-zone: "UTC0"
 # time-stamp-end: "; # UTC"
 # End: