configure, meson: detect Rust toolchain

Include the correct path and arguments to rustc in the native
and cross files (native compilation is needed for procedural
macros).

Based on the host architecture and OS, the compiler and optionally the argument
to --cpu, the Rust target triple can be detected automatically for either a
native or a cross compiler.

In general, it is only a matter of translating the architecture and OS, and
adding a machine to form the triple, but there are some special cases (e.g.
detecting soft vs. hard floating point on ARM) and some inconsistencies.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Link: https://lore.kernel.org/r/207d2640b32d511e9c27478ce3192f5bb0bf3169.1727961605.git.manos.pitsidianakis@linaro.org
[Leave disabled by default until CI covers the Rust code on supported
 distros. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -207,6 +207,8 @@ for opt do
   ;;
   --objcc=*) objcc="$optarg"
   ;;
+  --rustc=*) RUSTC="$optarg"
+  ;;
   --cpu=*) cpu="$optarg"
   ;;
   --extra-cflags=*)
@@ -252,6 +254,8 @@ python=
 download="enabled"
 skip_meson=no
 use_containers="yes"
+rust="disabled"
+rust_target_triple=""
 gdb_bin=$(command -v "gdb-multiarch" || command -v "gdb")
 gdb_arches=""
 
@@ -310,6 +314,7 @@ objcopy="${OBJCOPY-${cross_prefix}objcopy}"
 ld="${LD-${cross_prefix}ld}"
 ranlib="${RANLIB-${cross_prefix}ranlib}"
 nm="${NM-${cross_prefix}nm}"
+readelf="${READELF-${cross_prefix}readelf}"
 strip="${STRIP-${cross_prefix}strip}"
 widl="${WIDL-${cross_prefix}widl}"
 windres="${WINDRES-${cross_prefix}windres}"
@@ -317,6 +322,8 @@ windmc="${WINDMC-${cross_prefix}windmc}"
 pkg_config="${PKG_CONFIG-${cross_prefix}pkg-config}"
 sdl2_config="${SDL2_CONFIG-${cross_prefix}sdl2-config}"
 
+rustc="${RUSTC-rustc}"
+
 check_define() {
 cat > $TMPC <<EOF
 #if !defined($1)
@@ -425,6 +432,7 @@ fi
 # Please keep it sorted and synchronized with meson.build's host_arch.
 host_arch=
 linux_arch=
+raw_cpu=$cpu
 case "$cpu" in
   aarch64)
     host_arch=aarch64
@@ -658,6 +666,8 @@ for opt do
   ;;
   --objcc=*)
   ;;
+  --rustc=*)
+  ;;
   --make=*)
   ;;
   --install=*)
@@ -777,8 +787,14 @@ for opt do
   ;;
   --container-engine=*) container_engine="$optarg"
   ;;
+  --rust-target-triple=*) rust_target_triple="$optarg"
+  ;;
   --gdb=*) gdb_bin="$optarg"
   ;;
+  --enable-rust) rust=enabled
+  ;;
+  --disable-rust) rust=disabled
+  ;;
   # everything else has the same name in configure and meson
   --*) meson_option_parse "$opt" "$optarg"
   ;;
@@ -881,6 +897,7 @@ Advanced options (experts only):
                            at build time [$host_cc]
   --cxx=CXX                use C++ compiler CXX [$cxx]
   --objcc=OBJCC            use Objective-C compiler OBJCC [$objcc]
+  --rustc=RUSTC            use Rust compiler RUSTC [$rustc]
   --extra-cflags=CFLAGS    append extra C compiler flags CFLAGS
   --extra-cxxflags=CXXFLAGS append extra C++ compiler flags CXXFLAGS
   --extra-objcflags=OBJCFLAGS append extra Objective C compiler flags OBJCFLAGS
@@ -891,8 +908,9 @@ Advanced options (experts only):
   --python=PYTHON          use specified python [$python]
   --ninja=NINJA            use specified ninja [$ninja]
   --static                 enable static build [$static]
-  --without-default-features default all --enable-* options to "disabled"
-  --without-default-devices  do not include any device that is not needed to
+  --rust-target-triple=TRIPLE  compilation target for Rust code [autodetect]
+  --without-default-features   default all --enable-* options to "disabled"
+  --without-default-devices    do not include any device that is not needed to
                            start the emulator (only use if you are including
                            desired devices in configs/devices/)
   --with-devices-ARCH=NAME override default configs/devices
@@ -1166,6 +1184,132 @@ EOF
   fi
 fi
 
+##########################################
+# detect rust triple
+
+if test "$rust" != disabled && has "$rustc" && $rustc -vV > "${TMPDIR1}/${TMPB}.out"; then
+  rust_host_triple=$(sed -n 's/^host: //p' "${TMPDIR1}/${TMPB}.out")
+else
+  if test "$rust" = enabled; then
+    error_exit "could not execute rustc binary \"$rustc\""
+  fi
+  rust=disabled
+fi
+if test "$rust" != disabled && test -z "$rust_target_triple"; then
+  # arch and os generally matches between meson and rust
+  rust_arch=$host_arch
+  rust_os=$host_os
+  rust_machine=unknown
+  rust_osvariant=
+
+  # tweak rust_os if needed; also, machine and variant depend on the OS
+  android=no
+  case "$host_os" in
+  darwin)
+    # e.g. aarch64-apple-darwin
+    rust_machine=apple
+    ;;
+
+  linux)
+    # detect android/glibc/musl
+    if check_define __ANDROID__; then
+      rust_osvariant=android
+      android=yes
+    else
+      cat > $TMPC << EOF
+#define _GNU_SOURCE
+#include <features.h>
+#ifndef __USE_GNU
+error using musl
+#endif
+EOF
+      if compile_object; then
+        rust_osvariant=gnu
+      else
+        rust_osvariant=musl
+      fi
+    fi
+
+    case "$host_arch" in
+    arm)
+      # e.g. arm-unknown-linux-gnueabi, arm-unknown-linux-gnueabihf
+      write_c_skeleton
+      compile_object
+      if $READELF -A $TMPO | grep Tag_API_VFP_args: > /dev/null; then
+        rust_osvariant=${rust_osvariant}eabihf
+      else
+        rust_osvariant=${rust_osvariant}eabi
+      fi
+      ;;
+
+    mips64)
+      # e.g. mips64-unknown-linux-gnuabi64
+      rust_osvariant=${rust_osvariant}abi64
+      ;;
+    esac
+    ;;
+
+  netbsd)
+    # e.g. arm-unknown-netbsd-eabihf
+    test "$host_arch" = arm && rust_osvariant=eabihf
+    ;;
+
+  sunos)
+    rust_machine=pc
+    rust_os=solaris
+    ;;
+
+  windows)
+    # e.g. aarch64-pc-windows-gnullvm, x86_64-pc-windows-gnu (MSVC not supported)
+    rust_machine=pc
+    if test "$host_arch" = aarch64; then
+      rust_osvariant=gnullvm
+    else
+      rust_osvariant=gnu
+    fi
+    ;;
+  esac
+
+  # now tweak the architecture part, possibly based on pre-canonicalization --cpu
+  case "$host_arch" in
+  arm)
+    # preserve ISA version (armv7 etc.) from $raw_cpu if passed via --cpu
+    rust_arch=$raw_cpu
+    test "$rust_arch" = arm && test "$rust_os" != linux && rust_arch=armv7
+    ;;
+
+  mips|mips64)
+    # preserve ISA version (mipsisa64r6 etc.) and include endianness
+    rust_arch=${raw_cpu%el}
+    test "$bigendian" = no && rust_arch=${rust_arch}el
+    ;;
+
+  riscv32|riscv64)
+    # e.g. riscv64gc-unknown-linux-gnu, but riscv64-linux-android
+    test "$android" = no && rust_arch=${rust_arch}gc
+    ;;
+
+  sparc64)
+    if test "$rust_os" = solaris; then
+      rust_arch=sparcv9
+      rust_machine=sun
+    fi
+    ;;
+
+  x86_64)
+    # e.g. x86_64-unknown-linux-gnux32
+    test "$raw_cpu" = x32 && rust_osvariant=${rust_osvariant}x32
+    ;;
+  esac
+
+  if test "$android" = yes; then
+    # e.g. aarch64-linux-android
+    rust_target_triple=$rust_arch-$rust_os-$rust_osvariant
+  else
+    rust_target_triple=$rust_arch-$rust_machine-$rust_os${rust_osvariant:+-$rust_osvariant}
+  fi
+fi
+
 ##########################################
 # functions to probe cross compilers
 
@@ -1628,6 +1772,9 @@ if test "$container" != no; then
     echo "RUNC=$runc" >> $config_host_mak
 fi
 echo "SUBDIRS=$subdirs" >> $config_host_mak
+if test "$rust" != disabled; then
+  echo "RUST_TARGET_TRIPLE=$rust_target_triple" >> $config_host_mak
+fi
 echo "PYTHON=$python" >> $config_host_mak
 echo "MKVENV_ENSUREGROUP=$mkvenv ensuregroup $mkvenv_online_flag" >> $config_host_mak
 echo "GENISOIMAGE=$genisoimage" >> $config_host_mak
@@ -1764,12 +1911,20 @@ if test "$skip_meson" = no; then
   echo "c = [$(meson_quote $cc $CPU_CFLAGS)]" >> $cross
   test -n "$cxx" && echo "cpp = [$(meson_quote $cxx $CPU_CFLAGS)]" >> $cross
   test -n "$objcc" && echo "objc = [$(meson_quote $objcc $CPU_CFLAGS)]" >> $cross
+  if test "$rust" != disabled; then
+    if test "$rust_host_triple" != "$rust_target_triple"; then
+      echo "rust = [$(meson_quote $rustc --target "$rust_target_triple")]" >> $cross
+    else
+      echo "rust = [$(meson_quote $rustc)]" >> $cross
+    fi
+  fi
   echo "ar = [$(meson_quote $ar)]" >> $cross
   echo "dlltool = [$(meson_quote $dlltool)]" >> $cross
   echo "nm = [$(meson_quote $nm)]" >> $cross
   echo "pkgconfig = [$(meson_quote $pkg_config)]" >> $cross
   echo "pkg-config = [$(meson_quote $pkg_config)]" >> $cross
   echo "ranlib = [$(meson_quote $ranlib)]" >> $cross
+  echo "readelf = [$(meson_quote $readelf)]" >> $cross
   if has $sdl2_config; then
     echo "sdl2-config = [$(meson_quote $sdl2_config)]" >> $cross
   fi
@@ -1799,6 +1954,9 @@ if test "$skip_meson" = no; then
     echo "# Automatically generated by configure - do not modify" > $native
     echo "[binaries]" >> $native
     echo "c = [$(meson_quote $host_cc)]" >> $native
+    if test "$rust" != disabled; then
+      echo "rust = [$(meson_quote $rustc)]" >> $cross
+    fi
     mv $native config-meson.native
     meson_option_add --native-file
     meson_option_add config-meson.native
@@ -1817,6 +1975,7 @@ if test "$skip_meson" = no; then
   test "$pie" = no && meson_option_add -Db_pie=false
 
   # QEMU options
+  test "$rust" != "auto" && meson_option_add "-Drust=$rust"
   test "$cfi" != false && meson_option_add "-Dcfi=$cfi" "-Db_lto=$cfi"
   test "$docs" != auto && meson_option_add "-Ddocs=$docs"
   test -n "${LIB_FUZZING_ENGINE+xxx}" && meson_option_add "-Dfuzzing_engine=$LIB_FUZZING_ENGINE"

meson.build

@@ -4325,8 +4325,9 @@ else
 endif
 summary_info += {'Rust support':      have_rust}
 if have_rust
-  summary_info += {'rustc version':      rustc.version()}
-  summary_info += {'rustc':      ' '.join(rustc.cmd_array())}
+  summary_info += {'rustc version':   rustc.version()}
+  summary_info += {'rustc':           ' '.join(rustc.cmd_array())}
+  summary_info += {'Rust target':     config_host['RUST_TARGET_TRIPLE']}
 endif
 option_cflags = (get_option('debug') ? ['-g'] : [])
 if get_option('optimization') != 'plain'