Marvin,

ImageBase was saved in DR2 to help HOST debugger to locate the image base more easily, even though the HOST debugger could find the image base through searching the DOS image signagure.

The reason choosing DR1 and DR2 to save PDB & ImageBase contexts is just implementation only. And it could co-work with Debug Agent Lib implementation and SIMCS.  I am not sure whether is could co-work with INTEl System Debugging tools or not.

I don't understand why the new PeCoffLib implementation would break the existing debugging tools？Could you explain it more details?

Jeff
fanjianfeng@byosoft.com.cn
 
From: Marvin Häuser
Date: 2021-08-01 01:21
To: devel@edk2.groups.io
CC: Hao A Wu
Subject: [edk2-devel] SLDP: Usage of PE library context by debugger?
Good day everyone,
 
While refining the port of SourceLevelDebugPkg to my newly proposed
PeCoffLib rework (RFC upcoming), I noticed that the address of the PE
Image context is written to DR2 [1]. Because the UDK and Intel System
Studio debugging tools are closed source, I cannot verify what happens
to this value. Does the host read the library context and retrieve data
from it? If not, why is its address written to DR2? If so, this would
mean the new PeCoffLib implementation breaks the existing debugging
tools. The following questions would arise:
 
1) Which data are retrieved from the context structure? For GDB, I think
only the Image address and symbol file path are required (to load the
symbols), while PDB is saved in DR1 already.
2) Are there any plans to provide detailed documentation of the
host/client communication protocol?
3) Are there any plans to provide an open source debugger, or at least
the EDK II communication protocol portion?
 
Thank you for your time!
 
Best regards,
Marvin
 
 
[1]
https://github.com/tianocore/edk2/blob/610bcc69ed3d1e8c016332a1862465d41d95dd6c/SourceLevelDebugPkg/Library/PeCoffExtraActionLibDebug/PeCoffExtraActionLib.c#L126