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[PULL,2/8] docs: document breakpoint and watchpoint support

Message ID 20230510150658.1399087-3-alex.bennee@linaro.org
State Accepted
Commit ab9d29b0a4ab2fec433f18b809b66bc43db1d228
Headers show
Series [PULL,1/8] tests/docker: bump the xtensa base to debian:11-slim | expand

Commit Message

Alex Bennée May 10, 2023, 3:06 p.m. UTC
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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Patch

diff --git a/docs/system/gdb.rst b/docs/system/gdb.rst
index 453eb73f6c..7d3718deef 100644
--- a/docs/system/gdb.rst
+++ b/docs/system/gdb.rst
@@ -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
 ============================