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docs: document breakpoint and watchpoint support

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This varies by accelerator. Also mention the modern bear trap that is
ASLR.

Message-Id: <20230503091244.1450613-4-alex.bennee@linaro.org>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
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Alex Bennée 2023-05-02 15:23:50 +01:00
parent 3217b84f3c
commit ab9d29b0a4
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docs/system/gdb.rst
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@ -46,6 +46,28 @@ Here are some useful tips in order to use gdb on system code:
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.
Breakpoint and Watchpoint support
=================================
While GDB can always fall back to inserting breakpoints into memory
(if writable) other features are very much dependent on support of the
accelerator. For TCG system emulation we advertise an infinite number
of hardware assisted breakpoints and watchpoints. For other
accelerators it will depend on if support has been added (see
supports_guest_debug and related hooks in AccelOpsClass).
As TCG cannot track all memory accesses in user-mode there is no
support for watchpoints.
Relocating code
---------------
On modern kernels confusion can be caused by code being relocated by
features such as address space layout randomisation. To avoid
confusion when debugging such things you either need to update gdb's
view of where things are in memory or perhaps more trivially disable
ASLR when booting the system.
Debugging multicore machines
============================