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From: "simark at simark dot ca" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug gdb/28412] syscall that writes memory does not trigger hardware
 watchpoint.
Date: Sat, 09 Oct 2021 17:26:38 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D28412

Simon Marchi <simark at simark dot ca> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |simark at simark dot ca

--- Comment #1 from Simon Marchi <simark at simark dot ca> ---
(In reply to Yichao Yu from comment #0)
> When a watchpoint is set on `c` with `watch -l c` or `watch c`, the value=
 is
> changed by `read` without triggering the watch point. Turning off hardware
> watchpoint fixes the issue. Seems that when hardware watch point is used,
> checks needs to be added around syscalls to see if they modify memory?

That sounds doable (although at a cost).  GDB uses PTRACE_SYSCALL to cause =
the
program to stop on syscall entry only if the user has set up some syscall
catchpoints.  But it could also be enabled if the user has some hardware
watchpoints set.  When a thread exits, we would get an event, and we could
check all watchpoints, see if the memory they watch has changed.

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