configure: improve inference of compiler flags for pb builds (#829)

When building an pb variant like `tpb64l`, and even when building for
a platform without native-code support, the "configure" script may
still be able to infer suitable C compilation and linking flags for
the kernel. Add an `--os=...` flag that can be used to override that
inference in case it's not correct (as in the case of cross
compilation).

BUILDING

@@ -146,6 +146,14 @@ type of build and the installation location. For example,
 specifies the installation root. Run `./configure --help` for
 information on the supported options.
 
+For platforms without support for native-code compilation in Chez
+Scheme, use a machine specification like `-m=tpb64l`, which is a
+threaded, 64-bit, little-endian build. The "configure" script will
+still attept to infer compilation and linking flags for the kernel; if
+you need to give it a hint, you can use the `--os` flag with something
+like `--os=tXle`, which indicates a threaded configuration (due to the
+leading "t") on Linux (due to the trailing "le").
+
 The generated makefile mostly just ensures that a `zuo` executable is
 built in a `bin` directory, and then it defers the actual build work
 to `zuo`, which uses the "main.zuo" file. If you have `zuo` installed,

c/build.zuo

@@ -93,7 +93,7 @@
          kernel-srcs))
 
   (define kernel-asm-files
-    (if (glob-match? "*nt" (or (lookup 'defaultm) m))
+    (if (glob-match? "*nt" (or (lookup 'flagsm) m))
 	(cond
           [(and msvc?
                 (string=? arch "a6"))
@@ -510,7 +510,7 @@
             [config (hash-set config 'LDFLAGS (if (as-runtime-dll? config) "/MD" "/MT"))]
             [config (hash-set config 'LIBS "rpcrt4.lib ole32.lib advapi32.lib User32.lib")])
        config)]
-    [(and (glob-match? "*nt" (hash-ref config 'defaultm ""))
+    [(and (glob-match? "*nt" (hash-ref config 'flagsm ""))
           (glob-match? "pb*" (m->arch (hash-ref config 'm))))
      (config-merge config 'CFLAGS "-DFEATURE_WINDOWS")]
     [else config]))
@@ -554,7 +554,7 @@
 (define (for-windows? config)
   (or (is-msvc? config)
       (glob-match? "*nt" (hash-ref config 'm))
-      (glob-match? "*nt" (or (hash-ref config 'defaultm #f) ""))))
+      (glob-match? "*nt" (or (hash-ref config 'flagsm #f) ""))))
 
 (define (lib-build-suffix config)
   (if (is-msvc? config)

configure

@@ -49,8 +49,21 @@ else
     cflagsset=no    
 fi
 
+# Machine type to build:
 m=""
+
+# Working directory, defaults to $m
 w=""
+
+# Machine describing the OS that the kernel runs on, so it determines
+# default compiler and linker flags; when $m is a pb variant, then
+# this OS is inferred if not specified with `--osmachine=`
+flagsm=""
+
+# Used to select a default $m, but in the end corresponds to
+# the target machine for boot files when built via pb
+defaultm=""
+
 pb=no
 pbarch=no
 threads=yes
@@ -257,6 +270,9 @@ while [ $# != 0 ] ; do
     --machine=*)
       m=`echo $1 | sed -e 's/^--machine=//'`
       ;;
+    --os=*)
+      flagsm=`echo $1 | sed -e 's/^--os=//'`
+      ;;
     --boot=*)
       mboot=`echo $1 | sed -e 's/^--boot=//'`
       ;;
@@ -477,15 +493,6 @@ if [ $emscripten = yes ] ; then
     tm32=tpb32l
 fi
 
-case "$m" in
-    pb)
-        echo "Don't select pb using -m or --machine, because pb prefers to use the"
-        echo " machine as the kernel host machine. Instead, use --pb or --pbarch"
-        echo " to select a pb (portable bytecode) build."
-        exit 1
-        ;;
-esac
-
 if [ "$bits" = "" ] ; then
   # infer default bits; this will be irrelevant if a machine is specified
   if [ "$unamebits" != "" ] ; then
@@ -506,7 +513,14 @@ fi
 # to the host platform's threadedness, and we want that to default
 # the same way as when `--pb` is not used
 if [ "$threads" = "" ] ; then
-    defaultthreads=yes
+    case "$m" in
+        pb*)
+            defaultthreads=no
+            ;;
+        *)
+            defaultthreads=yes
+            ;;
+    esac
 else
     defaultthreads=$threads
 fi
@@ -542,36 +556,48 @@ if [ "$m" = "" ] ; then
   machine_supplied=no
   if [ $pb = yes ] ; then
      m=pb
-     if [ "$threads" = yes ] ; then m=t$m ; fi
-     if [ $bits = 64 ] ; then mpbhost=$m64 ; else mpbhost=$m32 ; fi
-     flagsm=$mpbhost
-     if [ "$mpbhost" = "" ] ; then
-         flagsm=unknown
+     if [ $bits = 64 ] ; then defaultflagsm=$m64 ; else defaultflagsm=$m32 ; fi
+     if [ "$defaultflagsm" = "" ] ; then
+         defaultflagsm=unknown
+     fi
+     if [ "$threads" = yes ] ; then
+         m=t$m
+         defaultflagsm=t$defaultflagsm
      fi
   else
     if [ "$unknownm" != "yes" ] ; then
         m=$defaultm
     fi
-    flagsm=$defaultm
-    # note that m (and flagsm) could still be "" at this point, in which
+    defaultflagsm=$defaultm
+    # note that m (and defaultflagsm) could still be "" at this point, in which
     # case "No suitable machine type" will be reported further below
   fi
 elif [ $pb = yes ] ; then
-  mpbhost=$m
-  flagsm=$m
+  defaultflagsm=$m
   m=pb
 else
-  flagsm=$m
+  case "${m}" in
+      pb*|tpb*)
+          defaultflagsm=$defaultm
+          ;;
+      *)
+          defaultflagsm=$m
+  esac
   defaultm=$m
 fi
 
 if [ $pbarch = yes ] ; then
     m=pb$bits$pbendian
     if [ "$defaultthreads" = yes ] ; then
         m=t$m
+        defaultflagsm=t$defaultflagsm
     fi
 fi
 
+if [ "$flagsm" = "" ] ; then
+    flagsm=$defaultflagsm
+fi
+
 if [ "$mboot" = "" ] ; then
     mboot="$m"
 else
@@ -623,6 +649,7 @@ if [ "$help" = "yes" ]; then
   echo "Options (defaults shown in parens):"
   echo "  --machine=<machine type>          explicitly specify machine type ($m)"
   echo "  -m=<machine type>                 same as --machine=<machine type> ($m)"
+  echo "  --os=<machine type>               specify OS as a machine type ($flagsm)"
   echo "  --threads                         specify threaded version ($threads)"
   echo "  --nothreads                       specify non-threaded version ($nothreads)"
   echo "  --32|--64                         specify 32/64-bit version ($bits)"
@@ -1042,6 +1069,10 @@ else
     configuringin=" in $w"
 fi
 
+if [ "$flagsm" != "$m" ] ; then
+    configuringin="$configuringin to run on $flagsm"
+fi
+
 if [ "$m" = "" ] ; then
     enableFrompb=no
     forceworkarea=no
@@ -1113,6 +1144,7 @@ srcdir=$srcdir
 upsrcdir=$upsrcdir
 m=$m
 defaultm=$defaultm
+flagsm=$flagsm
 mboot=$mboot
 buildKernelOnly=$buildKernelOnly
 enableFrompb=$enableFrompb