Thanks a lot !
Best regards,
Vincent.
Le 19/01/2023 à 18:39, Alex Bennée a écrit :
vincent Dupaquis <v.dupaquis@trusted-objects.com> writes:
(cc: chardev backend maintainers)
[[PGP Signed Part:Undecided]]
Hello,
I've tried to use the semihosting on qemu-system-arm (version 7.0), and was not able to redirect the
input/output to a pipe, for instance.
It seems I've declared the chardev correctly as I do not get any error message, but impossible for me to
redirect the input/output streams. I had to redirect stdout using tee and found another way to access stdin
(through the /dev/pts/x device I can obtain through the ps command).
I digged into the sources to understand what I was doing wrong, and could not :(
Has anyone ever tried to redirect both stdout/stdin while using semihosting ?
Should I expect a new behaviour with the latest version ?
I was using the following options :
-semihosting -chardev pipe,id=pipout,path=pipout -semihosting-config
enable=on,chardev=pipout
I've never tried with a pipe but I have got it working with sockets and
files. Is the pipe ever going to be bi-directional?
Anyway for reference:
./qemu-system-aarch64 -display none -serial mon:stdio \
-M virt -cpu max,pauth-impdef=on \
-semihosting-config enable=on,chardev=shcd \
-kernel ./tests/tcg/aarch64-softmmu/memory \
-chardev file,path=test.out,id=shcd
works as expected, re-directing output to the file. Unfortunately we
don't have many arm-softmmu tests. The only one we build
(test-armv6m-undef) only uses the exit semihosting call.
the pipe being created using mkfifo pipout beforehand.
Regards,
Vincent.
Le 10/01/2023 à 18:39, Alex Bennée a écrit :
The main reason to do this is to document our O_BINARY implementation
decision somewhere. However I've also moved some of the implementation
details out of qemu-options and added links between the two. As a
bonus I've highlighted the scary warnings about host access with the
appropriate RST tags.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
docs/about/features.rst | 10 ++---
docs/specs/index.rst | 1 +
docs/specs/semihosting.rst | 79 ++++++++++++++++++++++++++++++++++++++
qemu-options.hx | 27 +++++--------
4 files changed, 95 insertions(+), 22 deletions(-)
create mode 100644 docs/specs/semihosting.rst
diff --git a/docs/about/features.rst b/docs/about/features.rst
index 0808c35a4a..aed0f9b9a2 100644
--- a/docs/about/features.rst
+++ b/docs/about/features.rst
@@ -187,11 +187,11 @@ See `User Mode Emulation` for more details on running in this mode.
Semihosting
~~~~~~~~~~~~
-A number of guest architecture support semihosting which provides a
-way for guest programs to access the host system though a POSIX-like
-system call layer. This has applications for early software bring-up
-making it easy for a guest to dump data or read configuration files
-before a full operating system is implemented.
+A number of guest architecture support :ref:`Semihosting` which
+provides a way for guest programs to access the host system though a
+POSIX-like system call layer. This has applications for early software
+bring-up making it easy for a guest to dump data or read configuration
+files before a full operating system is implemented.
Some of those guest architectures also support semihosting in
user-mode making the testing of "bare-metal" micro-controller code
diff --git a/docs/specs/index.rst b/docs/specs/index.rst
index a58d9311cb..b46a16b2c8 100644
--- a/docs/specs/index.rst
+++ b/docs/specs/index.rst
@@ -21,3 +21,4 @@ guest hardware that is specific to QEMU.
acpi_erst
sev-guest-firmware
fw_cfg
+ semihosting
diff --git a/docs/specs/semihosting.rst b/docs/specs/semihosting.rst
new file mode 100644
index 0000000000..343eb4bbb3
--- /dev/null
+++ b/docs/specs/semihosting.rst
@@ -0,0 +1,79 @@
+.. _Semihosting:
+
+Semihosting
+-----------
+
+Semihosting is a feature provided by a number of guests that allow the
+program running on the target to interact with the host system. On
+real hardware this is usually provided by a debugger hooked directly
+to the system.
+
+Generally semihosting makes it easier to bring up low level code before a
+more fully functional operating system has been enabled. On QEMU it
+also allows for embedded micro-controller code which typically doesn't
+have a full libc to be run as "bare-metal" code under QEMU's user-mode
+emulation. It is also useful for writing test cases and indeed a
+number of compiler suites as well as QEMU itself use semihosting calls
+to exit test code while reporting the success state.
+
+Semihosting is only available using TCG emulation. This is because the
+instructions to trigger a semihosting call are typically reserved
+causing most hypervisors to trap and fault on them.
+
+.. warning::
+ Semihosting inherently bypasses any isolation there may be between
+ the guest and the host. As a result a program using semihosting can
+ happily trash your host system. You should only ever run trusted
+ code with semihosting enabled.
+
+Redirection
+~~~~~~~~~~~
+
+Semihosting calls can be re-directed to a (potentially remote) gdb
+during debugging via the :ref:`gdbstub<GDB usage>`. Output to the
+semihosting console is configured as a ``chardev`` so can be
+redirected to a file, pipe or socket like any other ``chardev``
+device.
+
+See :ref:`Semihosting Options<Semihosting Options>` for details.
+
+Supported Targets
+~~~~~~~~~~~~~~~~~
+
+Most targets offer a similar semihosting implementations with some
+minor changes to define the appropriate instruction to encode the
+semihosting call and which registers hold the parameters. They tend to
+presents a simple POSIX-like API which allows your program to read and
+write files, access the console and some other basic interactions.
+
+.. note::
+ QEMU makes an implementation decision to implement all file access
+ in ``O_BINARY`` mode regardless of the host operating system. This
+ is because gdb semihosting support doesn't make the distinction
+ between the modes and magically processing line endings can be confusing.
+
+.. list-table:: Guest Architectures supporting Semihosting
+ :widths: 10 10 80
+ :header-rows: 1
+
+ * - Architecture
+ - Modes
+ - Specification
+ * - Arm
+ - System and User-mode
+ - https://github.com/ARM-software/abi-aa/blob/main/semihosting/semihosting.rst
+ * - m68k
+ - System
+ - https://sourceware.org/git/?p=newlib-cygwin.git;a=blob;f=libgloss/m68k/m68k-semi.txt;hb=HEAD
+ * - mips
+ - System
+ - Unified Hosting Interface (MD01069)
+ * - Nios II
+ - System
+ - https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=libgloss/nios2/nios2-semi.txt;hb=HEAD
+ * - RISC-V
+ - System and User-mode
+ - https://github.com/riscv/riscv-semihosting-spec/blob/main/riscv-semihosting-spec.adoc
+ * - Xtensa
+ - System
+ - Tensilica ISS SIMCALL
diff --git a/qemu-options.hx b/qemu-options.hx
index 3aa3a2f5a3..de3a368f58 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4633,10 +4633,13 @@ DEF("semihosting", 0, QEMU_OPTION_semihosting,
QEMU_ARCH_MIPS | QEMU_ARCH_NIOS2 | QEMU_ARCH_RISCV)
SRST
``-semihosting``
- Enable semihosting mode (ARM, M68K, Xtensa, MIPS, Nios II, RISC-V only).
+ Enable :ref:`Semihosting` mode (ARM, M68K, Xtensa, MIPS, Nios II, RISC-V only).
- Note that this allows guest direct access to the host filesystem, so
- should only be used with a trusted guest OS.
+ .. warning::
+ Note that this allows guest direct access to the host filesystem, so
+ should only be used with a trusted guest OS.
+
+ .. _Semihosting Options:
See the -semihosting-config option documentation for further
information about the facilities this enables.
@@ -4648,22 +4651,12 @@ QEMU_ARCH_ARM | QEMU_ARCH_M68K | QEMU_ARCH_XTENSA |
QEMU_ARCH_MIPS | QEMU_ARCH_NIOS2 | QEMU_ARCH_RISCV)
SRST
``-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,userspace=on|off][,arg=str[,...]]``
- Enable and configure semihosting (ARM, M68K, Xtensa, MIPS, Nios II, RISC-V
+ Enable and configure :ref:`Semihosting` (ARM, M68K, Xtensa, MIPS, Nios II, RISC-V
only).
- Note that this allows guest direct access to the host filesystem, so
- should only be used with a trusted guest OS.
-
- On Arm this implements the standard semihosting API, version 2.0.
-
- On M68K this implements the "ColdFire GDB" interface used by
- libgloss.
-
- Xtensa semihosting provides basic file IO calls, such as
- open/read/write/seek/select. Tensilica baremetal libc for ISS and
- linux platform "sim" use this interface.
-
- On RISC-V this implements the standard semihosting API, version 0.2.
+ .. warning::
+ Note that this allows guest direct access to the host filesystem, so
+ should only be used with a trusted guest OS.
``target=native|gdb|auto``
Defines where the semihosting calls will be addressed, to QEMU
OpenPGP_signature