binfmt: Normalize host CPU architecture

Right now information regarding the family each CPU type belongs
to is recorded in two places: the large data table at the top of
the script, and the qemu_host_family() function.

We can make things better by mapping host CPU architecture to
QEMU target in the few cases where the two don't already match
and then using the data table to look up the family, same as
we're already doing for the guest CPU architecture.

Being able to reason in terms of QEMU target regardless of
whether we're looking at the host or guest CPU architecture will
come in handy to implement upcoming changes.

A couple of entries are dropped in the process: BePC and Power
Macintosh. I'm quite certain neither of those have ever been
reported as CPU architectures by Linux. I believe many more of
the entries that are carried forward could be dropped as well,
but I don't have the same level of confidence there so I
decided to play it safe just in case.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-ID: <20250127182924.103510-3-abologna@redhat.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

scripts/qemu-binfmt-conf.sh

@@ -144,35 +144,35 @@ loongarch64_magic='\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x
 loongarch64_mask='\xff\xff\xff\xff\xff\xff\xff\xfc\x00\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff'
 loongarch64_family=loongarch
 
-qemu_get_family() {
-    cpu=${HOST_ARCH:-$(uname -m)}
+# Converts the name of a host CPU architecture to the corresponding QEMU
+# target.
+#
+# FIXME: This can probably be simplified a lot by dropping most entries.
+#        Remember that the script is only used on Linux, so we only need to
+#        handle the strings Linux uses to report the host CPU architecture.
+qemu_normalize() {
+    cpu="$1"
     case "$cpu" in
-    amd64|i386|i486|i586|i686|i86pc|BePC|x86_64)
+    i[3-6]86)
         echo "i386"
         ;;
-    mips*)
-        echo "mips"
+    amd64)
+        echo "x86_64"
         ;;
-    "Power Macintosh"|ppc64|powerpc|ppc)
+    powerpc)
         echo "ppc"
         ;;
-    ppc64el|ppc64le)
-        echo "ppcle"
+    ppc64el)
+        echo "ppc64le"
         ;;
-    arm|armel|armhf|arm64|armv[4-9]*l|aarch64)
+    armel|armhf|armv[4-9]*l)
         echo "arm"
         ;;
-    armeb|armv[4-9]*b|aarch64_be)
+    armv[4-9]*b)
         echo "armeb"
         ;;
-    sparc*)
-        echo "sparc"
-        ;;
-    riscv*)
-        echo "riscv"
-        ;;
-    loongarch*)
-        echo "loongarch"
+    arm64)
+        echo "aarch64"
         ;;
     *)
         echo "$cpu"
@@ -309,7 +309,13 @@ EOF
 
 qemu_set_binfmts() {
     # probe cpu type
-    host_family=$(qemu_get_family)
+    host_cpu=$(qemu_normalize ${HOST_ARCH:-$(uname -m)})
+    host_family=$(eval echo \$${host_cpu}_family)
+
+    if [ "$host_family" = "" ] ; then
+        echo "INTERNAL ERROR: unknown host cpu $host_cpu" 1>&2
+        exit 1
+    fi
 
     # register the interpreter for each cpu except for the native one