[MinnowBoard] [edk2] How to DebugPrint in SMM at runtime?

[Andrew Fish]

> On Feb 13, 2015, at 3:24 PM, Edward Chicopee <edward.chicopee at gmail.com> wrote:
> 
> After finding out OVMF doesn't do SMM (on the EDK2-devel list), I decided to try working on a MinnowboardMax (hello minnow list too!)
> 
> I can see with the MinnowboardMax serial port debug output that if I write 0x01 to port 0xB2, it prints some things like 
> "PiSmmCommunicationHandler Enter"
> "PiSmmCommunicationHandler CommunicateHeader - 0"
> etc
> But when I search through the source code such lines don't seem to be present.
> 
> Eventually I found that they exist in a binary-only package, MinMAX076\Vlv2BinaryPkg\IA32DEBUG\IA32\PiSmmCommunicationSmm.efi
> Running strings on the binary seems to imply that it was linked against things like MdePkg\Library\BaseDebugLibSerialPort\DebugLib.c
> 
> As I did with OVMF, I just put a "DebugPrint (0xFFFFFFFF, "Hi from SMM\n"); into PiSmmCore.c. I see printout at boot time, but not at runtime upon forcing an SMI. I assume this is because it's just using some DXE DebugPrint which goes away at runtime? And I assume the reason the binary package can continue to DebugPrint into runtime is because it has (static?) linked against the DebugLib.c and so it contains all the code it needs internally? Or maybe the serial port configuration gets screwed up at runtime? But then I would expect after the first PiSmmCommunicationHandler print for it to be reconfigured properly.
> 
> I can see that PiSmmCode.inf says MdePkg/MdePkg.dec is under [Packages], and DebugLib is under [LibraryClasses], so maybe it's some other reason I can't see my DebugPrint in PiSmmCore.c at runtime only?
> 

Ed,

The INF defines the Library Class (think API) that the driver consumes. There is not a 1:1 mapping between a Library Class (API) and a Library Instance (Implementation). 

The DSC defines the which Library Instance is linked against the driver. The idea is the library choices are pushed into the platform build, and don’t exist in the INF. So for example if you get Reference Code for the Silicon you don’t need to modify it to use a different debug scheme. 

> So any help on how to see the print and/or (static?) link against the DebugLib.c that so

All linking in the edk2 is static linking. Dynamic stuff is all done in code via Protocols. 

> I can keep printing at runtime would be very appreciated.
> 

I don’t know the specifics of your platform but the best way to see what is going on is to generate a build report. You do this by adding a -y build.log to the build command. You can lookup the driver you care about and it will show you what libraries where used. If those libraries depended on libraries it will show you that too. 

A quick way to figure out the different DebugLib instances is to do something like:
~/work/src/edk2(master)>git grep DebugLib -- *.inf | grep LIBRARY_CLASS 
ArmPkg/Library/SemiHostingDebugLib/SemiHostingDebugLib.inf:24:  LIBRARY_CLASS                  = DebugLib|BASE SEC DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SAL_DRIVER DXE_SMM_DRIVER UEFI_APPLICATION UEFI_DRIVER
IntelFrameworkModulePkg/Library/PeiDxeDebugLibReportStatusCode/PeiDxeDebugLibReportStatusCode.inf:24:  LIBRARY_CLASS                  = DebugLib|DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SAL_DRIVER DXE_SMM_DRIVER SMM_CORE PEIM SEC PEI_CORE UEFI_APPLICATION UEFI_DRIVER
IntelFspPkg/Library/BaseFspDebugLibSerialPort/BaseFspDebugLibSerialPort.inf:21:  LIBRARY_CLASS                  = DebugLib
MdePkg/Library/BaseDebugLibNull/BaseDebugLibNull.inf:23:  LIBRARY_CLASS                  = DebugLib 
MdePkg/Library/BaseDebugLibSerialPort/BaseDebugLibSerialPort.inf:24:  LIBRARY_CLASS                  = DebugLib 
MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf:25:  LIBRARY_CLASS                  = DebugLib|DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SAL_DRIVER DXE_SMM_DRIVER UEFI_APPLICATION UEFI_DRIVER 
MdePkg/Library/UefiDebugLibStdErr/UefiDebugLibStdErr.inf:25:  LIBRARY_CLASS                  = DebugLib|DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SAL_DRIVER DXE_SMM_DRIVER UEFI_APPLICATION UEFI_DRIVER 
OvmfPkg/Library/PlatformDebugLibIoPort/PlatformDebugLibIoPort.inf:24:  LIBRARY_CLASS                  = DebugLib

This will show you the set of Library Instances that produce the DebugLib LibraryClass, and what module types they support. 

Good luck,

Andrew Fish

> Ed
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