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

Greg Clayton gclayton at apple.com
Mon Jun 9 10:14:58 PDT 2014

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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