gem5 semihosting

README.adoc

@@ -747,6 +747,7 @@ Alternatively, for the sake of tab completion, we also accept full paths inside
 To use gem5 instead of QEMU do:
 
 ....
+patch -d "$(./getvar gem5_src_dir)" -p 1 < patches/manual/gem5-semihost.patch && \
 ./configure --baremetal --gem5             && \
 ./build-gem5 --arch arm                    && \
 ./build-crosstool-ng --arch arm            && \
@@ -761,10 +762,9 @@ and then <<qemu-buildroot-setup,as usual>> open a shell with:
 ./gem5-shell
 ....
 
-TODO:
+TODO: the carriage returns are a bit different than in QEMU, see: <<gem5-baremetal-carriage-return>>.
 
-* the carriage returns are a bit different than in QEMU, see: <<gem5-baremetal-carriage-return>>.
-* semihosting is disabled, and all examples that rely on it fail, including  how to enable it? See <<gem5-semihosting>>
+The semihosting patch is required to enable <<semihosting>>, on which base functionality such as `exit()` depends, see also: https://stackoverflow.com/questions/52475268/how-to-enable-arm-semihosting-in-gem5/52475269#52475269
 
 Note that `./build-baremetal` requires the `--gem5` option, and generates separate executable images for both, as can be seen from:
 
@@ -9821,16 +9821,6 @@ Bibliography:
 * https://stackoverflow.com/questions/31990487/how-to-cleanly-exit-qemu-after-executing-bare-metal-program-without-user-interve/40957928#40957928
 * https://balau82.wordpress.com/2010/11/04/qemu-arm-semihosting/
 
-==== gem5 semihosting
-
-TODO how to enable it? <<config-ini>> contains:
-
-....
-root.system.semihosting=Null
-....
-
-and there are no hits under `configs/`.
-
 === gem5 baremetal carriage return
 
 TODO: our example is printing newlines without automatic carriage return `\r` as in:

baremetal/arch/aarch64/no_bootloader/semihost_exit.S

@@ -0,0 +1,10 @@
+.global mystart
+mystart:
+    mov x1, #0x26
+    movk x1, #2, lsl #16
+    str x1, [sp,#0]
+    mov x0, #0
+    str x0, [sp,#8]
+    mov x1, sp
+    mov w0, #0x18
+    hlt 0xf000

baremetal/interactive/README.adoc

@@ -0,0 +1 @@
+This folder contains examples that are not very testable: either are supposed to return 0, or are interactive, etc.

baremetal/interactive/exit1.c

@@ -0,0 +1,6 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+void main(void) {
+	exit(1);
+}

build-baremetal

@@ -119,6 +119,14 @@ def main(args, extra_args=None):
             bootloader_obj=bootloader_obj,
             common_obj=common_obj,
         )
+        build_dir(
+            'interactive',
+            gcc=gcc,
+            cflags=cflags,
+            entry_address=entry_address,
+            bootloader_obj=bootloader_obj,
+            common_obj=common_obj,
+        )
         arch_dir = os.path.join('arch', args.arch)
         if os.path.isdir(os.path.join(common.baremetal_src_dir, arch_dir)):
             build_dir(

patches/manual/gem5-semihost.patch

@@ -0,0 +1,12 @@
+diff --git a/configs/example/fs.py b/configs/example/fs.py
+index 3997ed76c..43bebcd66 100644
+--- a/configs/example/fs.py
++++ b/configs/example/fs.py
+@@ -376,5 +376,7 @@ if buildEnv['TARGET_ISA'] == "arm" and options.generate_dtb:
+             sys = getattr(root, sysname)
+             sys.dtb_filename = create_dtb_for_system(sys, '%s.dtb' % sysname)
+ 
++from m5.objects import ArmSemihosting
++test_sys.semihosting = ArmSemihosting()
+ Simulation.setWorkCountOptions(test_sys, options)
+ Simulation.run(options, root, test_sys, FutureClass)