[PATCH] Fix read and access watchpoint can't stop
Eli Zaretskii
eliz@gnu.org
Thu Jun 18 13:35:01 GMT 2020
> From: Hev <r@hev.cc>
> Date: Thu, 18 Jun 2020 10:05:14 +0800
> Cc: gdb-patches@sourceware.org
>
> > > /* We were stopped by a hardware watchpoint, but the target could
> > > not report the data address. We must check the watchpoint's
> > > value. Access and read watchpoints are out of luck; without
> >
> > The comment below the line you suggest to modify explains why we don't
> > handle access and read watchpoints here. So I don't understand the
> > rationale for this change (it might be a good idea to explain it in
> > more detail in the log message). What am I missing?
> >
> > Thanks.
>
> This problem only occurs on the target that target_stopped_data_address() returns false, and
> b->watchpoint_triggered is set to watch_triggered_unknown when watchpoint is triggered. so, In
> bpstat_check_watchpoint(), the last branch needs to be hit to enable check value:
>
> 4961 int must_check_value = 0;
> 4962
> 4963 if (b->type == bp_watchpoint)
> 4964 /* For a software watchpoint, we must always check the
> 4965 watched value. */
> 4966 must_check_value = 1;
> 4967 else if (b->watchpoint_triggered == watch_triggered_yes)
> 4968 /* We have a hardware watchpoint (read, write, or access)
> 4969 and the target earlier reported an address watched by
> 4970 this watchpoint. */
> 4971 must_check_value = 1;
> 4972 else if (b->watchpoint_triggered == watch_triggered_unknown
> 4973 && b->type == bp_hardware_watchpoint)
> 4974 /* We were stopped by a hardware watchpoint, but the target could
> 4975 not report the data address. We must check the watchpoint's
> 4976 value. Access and read watchpoints are out of luck; without
> 4977 a data address, we can't figure it out. */
> 4978 must_check_value = 1;
>
> However, the b->type is the actual watchpoint type, bp_hardware_watchpoint for write-only,
> bp_read_watchpoint for read-only, and bp_access_watchpoint for read-write, so it will not hit when read-only
> and read-write watching.
>
> On mips we don't know the low order 3 bits of the data address, so we must return false in
> stopped_data_address(). This is why we have not found the problem on other platforms (x86/Aarch64/...).
I understand, but how will this work on MIPS, given that
is_hardware_watchpoint allows any type of watchpoints? How will GDB
know which watchpoint triggered if there's no address?
And what is the value of bs->breakpoint_at, and how is it different
from b->type?
Thanks.
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