qemu: build variants

README.adoc

@@ -8445,6 +8445,19 @@ This technique is implemented semi-hackishly by moving symlinks around inside th
 
 ==== gem5 build variants
 
+Analogous to the <<linux-kernel-build-variants>> but with the `-Q` option instead:
+
+....
+./build
+git -C qemu checkout v2.12.0
+./build -Q v4.16
+git -C qemu checkout -
+./run
+./run -Q v4.16
+....
+
+==== gem5 build variants
+
 Analogous to the <<linux-kernel-build-variants>> but with the `-M` option instead:
 
 ....

build

@@ -209,7 +209,9 @@ symlink_buildroot_variant() (
 )
 symlink_buildroot_variant "$common_linux_custom_dir" "$common_linux_variant_dir"
 symlink_buildroot_variant "$common_qemu_custom_dir" "$common_qemu_variant_dir"
-symlink_buildroot_variant "$common_qemu_guest_custom_dir" "$common_qemu_guest_variant_dir"
+# TODO: this breaks the build. But then I noticed that it wouldn't make sense,
+# because this is a guest tool, and we don't have image variants yet. Some other day maybe.
+#symlink_buildroot_variant "$common_qemu_guest_custom_dir" "$common_qemu_guest_variant_dir"
 
 # Manage gem5 variants.
 if "$gem5"; then

build-usage.adoc

@@ -35,6 +35,7 @@
                              on top of it.
 |`-M` |`VARIANT`            |gem5 build variant.
 |`-p` |                     |Pass extra arguments to the `rootfs_post_build_script`.
+|`-Q` |`VARIANT`            |QEMU build variant.
 |`-S` |                     |Don't build QEMU with SDL support.
                              Graphics such as X11 won't work, only the terminal.
 |`-s` |                     |Add a custom suffix to the build.

common

@@ -112,6 +112,12 @@ set_common_vars() {
       ;;
   esac
   common_linux_image="${common_linux_variant_dir}/${common_linux_image}"
+  if "$common_prebuilt"; then
+    common_mkdir
+    common_qemu_executable="qemu-system-${arch}"
+  else
+    common_qemu_executable="${common_qemu_variant_dir}/${arch}-softmmu/qemu-system-${arch}"
+  fi
 
   # Ports.
   common_run_id_number="$(echo "$common_run_id" | cut -d . -f 2)"
@@ -150,6 +156,7 @@ common_gem5_default_src_dir="${root_dir}/gem5/gem5"
 common_gem5_non_default_src_root_dir="${data_dir}/gem5"
 common_gem5_worktree=
 common_gem5_variant=default
+common_prebuilt=false
 common_run_id=0
 f="${data_dir}/cli"
 if [ -f "$f" ]; then

run

@@ -26,7 +26,6 @@ initrd=false
 initramfs=false
 memory=256M
 nographic=true
-prebuilt=false
 root=
 tmux=false
 tmux_args=
@@ -35,7 +34,7 @@ trace_enabled=false
 # just to prevent QEMU from emitting a warning that '' is not valid.
 trace_type=pr_manager_run
 vnc=
-while getopts a:c:DdE:e:F:f:G:ghIiKkL:M:m:N:n:PT:t:U:uVX:x OPT; do
+while getopts a:c:DdE:e:F:f:G:ghIiKkL:M:m:N:n:PQ:T:t:U:uVX:x OPT; do
   case "$OPT" in
     a)
       arch="$OPTARG"
@@ -106,7 +105,10 @@ while getopts a:c:DdE:e:F:f:G:ghIiKkL:M:m:N:n:PT:t:U:uVX:x OPT; do
       common_run_id="$OPTARG"
       ;;
     P)
-      prebuilt=true
+      common_prebuilt=true
+      ;;
+    Q)
+      common_qemu_variant="$OPTARG"
       ;;
     T)
       trace_enabled=true
@@ -256,16 +258,10 @@ else
     extra_flags_qemu="$extra_flags_qemu -serial 'tcp::${common_gdb_port},server,nowait' \\
 "
   fi
-  if "$prebuilt"; then
-    common_mkdir
-    qemu_executable="qemu-system-${arch}"
-  else
-    qemu_executable="${buildroot_out_dir}/host/usr/bin/qemu-system-${arch}"
-  fi
   extra_flags="${extra_flags_qemu} ${extra_flags}"
   qemu_common="\
 ${debug_vm} \
-${qemu_executable} \\
+${common_qemu_executable} \\
 -device rtl8139,netdev=net0 \\
 -gdb 'tcp::${common_gdb_port}' \\
 -kernel '${common_linux_image}' \\
@@ -297,7 +293,7 @@ ${vnc}"
       if "$kgdb"; then
         extra_append="${extra_append} kgdboc=ttyS0,115200"
       fi
-      if "$prebuilt"; then
+      if "$common_prebuilt"; then
         custom_devices=
       else
         custom_devices="-device lkmc_pci_min \\