(nuttx) 02/02: Documentation/qemu-armv8a: Note fork() and the semihosting flag.

[ac...@apache.org]

This is an automated email from the ASF dual-hosted git repository.

acassis pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/nuttx.git

commit a2a1f881e29f3aacd7f064508aa601386dee2243
Author: Marco Casaroli <ma...@gmail.com>
AuthorDate: Mon Aug 10 22:03:13 2026 +0200

    Documentation/qemu-armv8a: Note fork() and the semihosting flag.
    
    The kernel mode section shows the QEMU command but does not say why
    -semihosting is there.  Without it the guest traps in smh_call and stops in
    AppBringUp, which reads as a kernel defect and is not one.  It cost me a
    session once.
    
    Also state that a kernel build is the only mode on this board with POSIX
    fork(), and that vfork() is available in every mode.
    
    Assisted-by: Claude Opus 5 (1M context) <no...@anthropic.com>
    Signed-off-by: Marco Casaroli <ma...@gmail.com>
---
 .../platforms/arm64/qemu/boards/qemu-armv8a/index.rst          | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/platforms/arm64/qemu/boards/qemu-armv8a/index.rst b/Documentation/platforms/arm64/qemu/boards/qemu-armv8a/index.rst
index 5b488b0a147..675a02bb5f5 100644
--- a/Documentation/platforms/arm64/qemu/boards/qemu-armv8a/index.rst
+++ b/Documentation/platforms/arm64/qemu/boards/qemu-armv8a/index.rst
@@ -463,6 +463,16 @@ Running with QEMU:
      -net none -chardev stdio,id=con,mux=on -serial chardev:con \
      -mon chardev=con,mode=readline -kernel ./nuttx
 
+``-semihosting`` is necessary.  A kernel build loads its applications over
+hostfs.  Without the flag the guest traps in ``smh_call`` and stops in
+``AppBringUp``, which looks like a kernel defect and is not one.
+
+A kernel build gives each process its own address environment.  This is the
+only build mode on this board that provides POSIX ``fork()``:  the child
+receives its own copy of the memory of the parent, at the same virtual
+addresses.  ``vfork()`` is available in every build mode.
+
+
 Inter-VM share memory Device (ivshmem)
 --------------------------------------