docs/system: convert Texinfo documentation to rST

Apart from targets.rst, which was written by hand, this is an automated
conversion obtained with the following command:

  makeinfo --force -o - --docbook \
    -D 'qemu_system_x86 QEMU_SYSTEM_X86_MACRO' \
    -D 'qemu_system     QEMU_SYSTEM_MACRO' \
    $texi | pandoc -f docbook -t rst+smart | perl -e '
      $/=undef;
      $_ = <>;
      s/^-  − /-  /gm;
      s/QEMU_SYSTEM_MACRO/|qemu_system|/g;
      s/QEMU_SYSTEM_X86_MACRO/|qemu_system_x86|/g;
      s/(?=::\n\n +\|qemu)/.. parsed-literal/g;
      s/:\n\n::$/::/gm;
      print' > $rst

In addition, the following changes were made manually:

- target-i386.rst and target-mips.rst: replace CPU model documentation with
  an include directive

- monitor.rst: replace the command section with a comment

- images.rst: add toctree

- target-arm.rst: Replace use of :math: (which Sphinx complains
  about) with :sup:, and hide it behind |I2C| and |I2C| substitutions.

Content that is not @included remains exclusive to qemu-doc.texi.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200228153619.9906-20-peter.maydell@linaro.org
Message-id: 20200226113034.6741-19-pbonzini@redhat.com
[PMM: Fixed target-arm.rst use of :math:; remove out of date
 note about images.rst from commit message; fixed expansion
 of |qemu_system_x86|; use parsed-literal in invocation.rst
 when we want to use |qemu_system_x86|; fix incorrect subsection
 level for "OS requirements" in target-i386.rst; fix incorrect
 syntax for making links to other sections of the manual]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

docs/system/gdb.rst

@@ -0,0 +1,81 @@
+.. _gdb_005fusage:
+
+GDB usage
+---------
+
+QEMU has a primitive support to work with gdb, so that you can do
+'Ctrl-C' while the virtual machine is running and inspect its state.
+
+In order to use gdb, launch QEMU with the '-s' option. It will wait for
+a gdb connection:
+
+.. parsed-literal::
+
+   |qemu_system| -s -kernel bzImage -hda rootdisk.img -append "root=/dev/hda"
+   Connected to host network interface: tun0
+   Waiting gdb connection on port 1234
+
+Then launch gdb on the 'vmlinux' executable::
+
+   > gdb vmlinux
+
+In gdb, connect to QEMU::
+
+   (gdb) target remote localhost:1234
+
+Then you can use gdb normally. For example, type 'c' to launch the
+kernel::
+
+   (gdb) c
+
+Here are some useful tips in order to use gdb on system code:
+
+1. Use ``info reg`` to display all the CPU registers.
+
+2. Use ``x/10i $eip`` to display the code at the PC position.
+
+3. Use ``set architecture i8086`` to dump 16 bit code. Then use
+   ``x/10i $cs*16+$eip`` to dump the code at the PC position.
+
+Advanced debugging options:
+
+The default single stepping behavior is step with the IRQs and timer
+service routines off. It is set this way because when gdb executes a
+single step it expects to advance beyond the current instruction. With
+the IRQs and timer service routines on, a single step might jump into
+the one of the interrupt or exception vectors instead of executing the
+current instruction. This means you may hit the same breakpoint a number
+of times before executing the instruction gdb wants to have executed.
+Because there are rare circumstances where you want to single step into
+an interrupt vector the behavior can be controlled from GDB. There are
+three commands you can query and set the single step behavior:
+
+``maintenance packet qqemu.sstepbits``
+   This will display the MASK bits used to control the single stepping
+   IE:
+
+   ::
+
+      (gdb) maintenance packet qqemu.sstepbits
+      sending: "qqemu.sstepbits"
+      received: "ENABLE=1,NOIRQ=2,NOTIMER=4"
+
+``maintenance packet qqemu.sstep``
+   This will display the current value of the mask used when single
+   stepping IE:
+
+   ::
+
+      (gdb) maintenance packet qqemu.sstep
+      sending: "qqemu.sstep"
+      received: "0x7"
+
+``maintenance packet Qqemu.sstep=HEX_VALUE``
+   This will change the single step mask, so if wanted to enable IRQs on
+   the single step, but not timers, you would use:
+
+   ::
+
+      (gdb) maintenance packet Qqemu.sstep=0x5
+      sending: "qemu.sstep=0x5"
+      received: "OK"