SLDP: Usage of PE library context by debugger?

SLDP: Usage of PE library context by debugger?

[Marvin Häuser]

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

Re: [edk2-devel] SLDP: Usage of PE library context by debugger?

[Ni, Ray]

Marvin,
Host assumes first 8-byte (little endian) of memory pointed by DR2 is the value of Image base address.
DR1 points to the PDB path (I am sure you noticed that in the SourceLevelDebugPkg code).

There is no plan to provide detailed documentation of host/client communication protocol. So far, the brief explanation can be seen in SourceLevelDebugPkg\Include\TransferProtocol.h.

I admit that if the old me had the mindset of today's me, a detailed markdown doc should have been provided in SourceLevelDebugPkg.
I will check internally on the open source plan, but please don't heavily rely on that.

Thanks,
Ray

-----Original Message-----
From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Marvin H?user
Sent: Sunday, August 1, 2021 1:21 AM
To: devel@edk2.groups.io
Cc: Wu, Hao A <hao.a.wu@intel.com>
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

Re: [edk2-devel] SLDP: Usage of PE library context by debugger?

[Jeff Fan]

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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
 
 

 
 
 

[-- Attachment #2: Type: text/html, Size: 4348 bytes --]

Re: [edk2-devel] SLDP: Usage of PE library context by debugger?

[Marvin Häuser]

02.08.2021 05:09:29 Ni, Ray <ray.ni@intel.com>:

> Marvin,
> Host assumes first 8-byte (little endian) of memory pointed by DR2 is the value of Image base address.

Thanks Ray! So I can be confident no further data from the context are or will be queried and I can just publish the Image base from the stack for example?

Maybe another thing, is the Image base address used for anything but loading the symbols (analogous to GCC "add-symbol-file")? E.g. does it ever try to read and parse the Image header? Mostly I am interested in how changes to the TE format would affect the tool.

Best regards,
Marvin

> DR1 points to the PDB path (I am sure you noticed that in the SourceLevelDebugPkg code).
>
> There is no plan to provide detailed documentation of host/client communication protocol. So far, the brief explanation can be seen in SourceLevelDebugPkg\Include\TransferProtocol.h.
>
> I admit that if the old me had the mindset of today's me, a detailed markdown doc should have been provided in SourceLevelDebugPkg.
> I will check internally on the open source plan, but please don't heavily rely on that.

Thanks!

>
> Thanks,
> Ray
>
> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Marvin H?user
> Sent: Sunday, August 1, 2021 1:21 AM
> To: devel@edk2.groups.io
> Cc: Wu, Hao A <hao.a.wu@intel.com>
> 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
>
>
> 

Re: [edk2-devel] SLDP: Usage of PE library context by debugger?

[Marvin Häuser]

02.08.2021 06:51:39 Jeff Fan <fanjianfeng@byosoft.com.cn>:

> 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.

Good day Jeff,

Thanks for your response!

I've read that Intel System Debugger superseded the UDK debugging tool, 
maybe that was incorrect though. I use GDB. :)

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

Please refer to the mail from Ray and my response. It is not the Image 
base address that is saved in DR2, but the PeCoffLib context address, 
and my new library simply has a new context structure for various 
reasons.

Best regards,
Marvin

> 
> ----------------------------------------
> 
> Jeff
> fanjianfeng@byosoft.com.cn
> 
>  
> *From:* Marvin Häuser[mhaeuser@posteo.de]
> *Date:* 2021-08-01 01:21
> *To:* devel@edk2.groups.io
> *CC:* Hao A Wu[hao.a.wu@intel.com]
> *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
>  
>  
>  
>  
>  
>