Ray,
How do you know that the debugger does not automatically set breakpoints to
enable features? We have these kind of features in our debugger.
How do you clear the breakpoints? You need the debugger to stop prior to a
state change to clear the breakpoints, and to do this you you need the
callback.
As far as I can tell all the calls to SaveAndSetDebugTimerInterrupt (FALSE),
that are not internal to the debugger, imply the debugger needs to undo any
state that could cause an exception (S/W breakpoints injected in the code, and
H/W breakpoint registers). If you look most of the calls to
SaveAndSetDebugTimerInterrupt (FALSE) have to do with an IDT switch and the new
IDT will cause a system crash
All the following points could cause crashes if the debugger leaves behind
state that causes an exception.
BootScriptEcecutorDxe: S3BootScriptExecutorEntryFunction()
S3ResumePei: S3RestoreConfig2()
CapsulePei: Thunk32To64()
DXE IPL: HandOffToDxeCore() with PcdDxeIplSwitchToLongMode
DXE Core: CoreExitBootServices()
CSM: GenericLegacyBoot()
Thus the debugger should only leave behind system state that can cause an
exception if it is hooked into the IDT. If the IDT is going to be changed then
the debugger needs to be notified. The debugger should not hard crash the
system into a jmp $ loop if I as a user pick the wrong watchpoint to set in the
debugger, of set a breakpoint on _ModuleEntryPoint in the DXE Core.
At this point I'm working around this issue by disabling all debugger exception
sources when SaveAndSetDebugTimerInterrupt (FALSE) is called. This is a much
bigger issue on X64 than on ARM or IPF as the 32-bit to 64-bit mode changes are
causing most of the issues. The OS boot issue is generic.
Andrew Fish
On Aug 28, 2012, at 9:44 AM, Ni, Ruiyu wrote:
> Andrew,
> In my opinion, if user sets software/hardware breakpoints and doesn’t clear
> them before booting to runtime. The result is undefined. User is responsible
> to clear the breakpoints.
>
> Thanks,
> Ray
>
> From: Andrew Fish [mailto:[email protected]]
> Sent: Wednesday, August 29, 2012 12:21 AM
> To: [email protected]
> Subject: Re: [edk2] DebugAgentLib question
>
> Jeff,
>
> The location you note is very far into PEI Core Init. In the DXE Core the
> debugger is initialized right away, and in my local copy that is what I did
> in the PEI Core. Initing early implies you need to use InitializeDebugAgent
> () Function callback so the debugger context can be stored on the stack.
> Given the context is on the stack the 2nd call is needed to migrate the data
> to the stack that ends up on moved into system memory. It kind of makes
> sense if you think about it that if you want to start the debugger as early
> as possible in the PEI Core you need to use a scheme that is similar to the
> SEC scheme.
>
> I'm a little worried that almost every place we have a call to
> SaveAndSetInterruptTimer () to disable the interrupt timer we need to also
> stop the debugger. What happens if the debugger sets a port 0x80 trap and the
> IDT is switched over for DXE IPL or S3 resume? Seems like you will crash in
> the stub IDTs set up for these new environments. I'm thinking of making my
> implementation of SaveAndSetDebugTimerInterrupt() turn off the debug
> registers too, but this is not really a clean solution. We could add an
> InitFlag to IntializeDebugAgent() for this, but I'm worried this will start
> to leak chunks of the debugger that are not needed into various modules (DXE
> IPL, S3 Resume, ...).
>
> Andrew Fish
>
>
>
>
>
> On Aug 27, 2012, at 10:40 PM, Fan, Jeff wrote:
>
>
> Andrew,
>
> We have defined one InitFlag DEBUG_AGENT_INIT_PEI, which could be used by one
> PEI module to initialize Debug Agent. I think it also could be used by PEI
> Core.
>
> For example,
> It could be invoked in PEI Core at below,
> //
> // Initialize PEI Core Services
> //
> InitializeMemoryServices (&PrivateData, SecCoreData, OldCoreData);
> InitializePpiServices (&PrivateData, OldCoreData);
>
> InitializeDebugAgent (DEBUG_AGENT_INIT_PEI, NULL, NULL);
>
> Debug Agent Library instance could initialize Debug Agent and use HOB service
> to save some private contents. HOB services will be consistence before/after
> physical memory is ready.
> Debug Agent Library instance also could register one PPI callback function on
> gEfiPeiMemoryDiscoveredPpiGuid, to send memory ready packet to HOST when
> memory is ready.
>
> Does it meet your requirement?
>
> Now I think DEBUG_AGENT_INIT_PEI_POSTMEM is not needed. If you encountered
> some issue when enabling Debug Agent in PEI Core module, we could revisit
> this flag at that time.
>
> Thanks!
> Jeff
>
> From: Andrew Fish [mailto:[email protected]]
> Sent: Tuesday, August 28, 2012 2:45 AM
> To: [email protected]
> Subject: Re: [edk2] DebugAgentLib question
>
> Jeff,
>
> Since we need to add an InitFlag, can we also add
> DEBUG_AGENT_INIT_PEI_POSTMEM?
>
> The code base does not seem to offer the option of having the debugger be
> part of the PEI Core, which I think is a design bug. I could envision system
> architectures where it is not wise to have a debugger integrated into the
> SEcurity Core, but a debugger for PEI is till wanted. So I think the PEI Core
> should have InitializeDebugagent() calls for DEBUG_AGENT_INIT_PEI, and
> DEBUG_AGENT_INIT_PEI_POSTMEM.
>
> Thanks,
>
> Andrew Fish
>
>
>
>
>
>
> On Aug 27, 2012, at 1:15 AM, Fan, Jeff wrote:
>
>
>
> Andrew,
>
> Good catch! Now, only Debug Timer interrupt was disabled before hand-off to
> OS.
>
> Besides Debug Registers, we also need to think how to clear the soft break
> points set by WinDbg or GDB in runtime services or in SMM code. One new
> InitFlag could be introduced to help HOST debugger to clear such break points
> if needed.
>
> Jeff
> From: Andrew Fish [mailto:[email protected]]
> Sent: Saturday, August 25, 2012 3:01 AM
> To: [email protected]
> Subject: [edk2] DebugAgentLib question
>
> #define DEBUG_AGENT_INIT_PREMEM_SEC 1
> #define DEBUG_AGENT_INIT_POSTMEM_SEC 2
> #define DEBUG_AGENT_INIT_DXE_CORE 3
> #define DEBUG_AGENT_INIT_SMM 4
> #define DEBUG_AGENT_INIT_ENTER_SMI 5
> #define DEBUG_AGENT_INIT_EXIT_SMI 6
> #define DEBUG_AGENT_INIT_S3 7
> #define DEBUG_AGENT_INIT_DXE_AP 8
> #define DEBUG_AGENT_INIT_PEI 9
> #define DEBUG_AGENT_INIT_DXE_LOAD 10
> #define DEBUG_AGENT_INIT_DXE_UNLOAD 11
>
> I was looking for a InitializeDebugAgent() InitFlag to turn off the debugger
> on boot? I was worried that if debug register were active when the OS boots
> that may cause an issue. Is it safe to assume the OS would clear debug
> registers prior to switching over the IDT? That seems to be implied by this
> interface?
>
> Andrew Fish
>
> https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2/MdeModulePkg/Include/Library/DebugAgentLib.h
>
>
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