[lldb-dev] qHostInfo proposal to add breakpoint pc offset

[Ted Woodward]

That was actually my first thought, but then I found m_breakpoint_pc_offset
and thought it would be useful to expose it via RSP instead of just by
target definition file.

My implementation keeps the same behavior if the GDB server doesn't use
bp_pc_decr; it sets m_breakpoint_pc_offset to 0.

Ted 

-----Original Message-----
From: Greg Clayton [mailto:gclayton at apple.com] 
Sent: Monday, June 09, 2014 12:15 PM
To: Ted Woodward
Cc: lldb-dev at cs.uiuc.edu
Subject: Re: [lldb-dev] qHostInfo proposal to add breakpoint pc offset

On Jun 6, 2014, at 6:56 AM, Ted Woodward <ted.woodward at codeaurora.org>
wrote:
> 
> Yes - we have 2 GDB servers. One is in a simulator, and uses "hardware"
> breakpoints. These give us the PC correctly. The other is a stub 
> running on hardware that uses software breakpoints, and gives us PC+4. 
> We could change it, but we're using GDB to talk to it right now, and GDB
expects PC+4.

Maybe if one of the LLDB specific packets is sent to your GDB server
(qHostInfo would be a good one) you can switch over to returning the correct
PC? Then you can still work with GDB and LLDB. 
> 
> Ted
> 
> -----Original Message-----
> From: Greg Clayton [mailto:gclayton at apple.com]
> Sent: Thursday, June 05, 2014 7:02 PM
> To: Ted Woodward
> Cc: lldb-dev at cs.uiuc.edu
> Subject: Re: [lldb-dev] qHostInfo proposal to add breakpoint pc offset
> 
> It is always better if the GDB server can do the backing up of the PC 
> and we generally want this to happen. We don't always know how 
> breakpoints are set when we use the Z packets to set/clear 
> breakpoints. If there are hardware resources, then a breakpoint might 
> get set as a hardware breakpoint and not require the backing up of the 
> PC. Again, these are all details that the GDB server should be in 
> charge of. If you hit a breakpoint that was set by the user, then the 
> PC should be backed up. If you hit a hard coded breakpoint trap that was
compiled in to the code, then you don't backup the PC.
> 
> I believe this support was added for one GDB server that didn't do the 
> backing up, but I would rather not have every GDB server have to tell 
> us that. Do you have one such GDB server that doesn't backup the PC 
> when it should be?
> 
> Greg
> 
>> On Jun 5, 2014, at 1:49 PM, Ted Woodward 
>> <ted.woodward at codeaurora.org>
> wrote:
>> 
>> On some architectures, when a breakpoint is hit, the PC is set to a
> different value and needs to be adjusted. This is handled in 
> ProcesGDBRemote.cpp by the variable m_breakpoint_pc_offset. The 
> problem is this variable is only set via a python target definition file.
>> 
>> 
>> 
>> I propose extending qHostInfo to add bp_pc_decr:<offset>.
> m_breakpoint_pc_offset would be set to this signed integer.
>> 
>> 
>> 
>> Ted
>> 
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> 
>