Re: Incompatible implementat ion of 'x' packet in GDB vs LLDB

On 28/01/2025 09:26, Pavel Labath via Gdb wrote:
> Hello everyone, an lldb dev here :)
> 
> I'm sorry for the trouble our implementation of 'x' has caused. I have 
> to admit I was surprised to find that the packet was not in the gdb 
> documentation already. It's been implemented in lldb for as long as I 
> can remember (~10 years), and the new packets we're adding nowadays have 
> much longer names, so I had assumed that it was always a part of the gdb 
> spec.
> 
> For what it's worth, I think your definition of the packet makes much 
> more sense. LLDB's definition is indeed ambiguous (and I didn't realize 
> how ambiguous until now) -- it cannot distinguish between a (truncated?) 
> memory read and an error. This behavior is not completely easy to 
> trigger because lldb will by default round the memory reads to 512-byte 
> boundaries (so truncation is unlikely), but with the right commands, I 
> was able to get it to treat valid memory as an error.
> 
> For this reason, I am going to propose to migrate lldb to the gdb 
> ("official") definition of the packet. Since we have users which need 
> (fairly long) windows of compatibility with old server, this is going to 
> require method to detect the implementation in use, so I'd like to reuse 
> the same mechanism that's going to be used in gdb (both the zero length 
> probe and the qSupported method seem fine to me).
> 
> regards,
> Pavel

And this 
<https://discourse.llvm.org/t/rfc-fixing-incompatibilties-of-the-x-packet-w-r-t-gdb/84288/1> 
is the lldb thread for that.

pl