Re: [PATCH 4/4] ArmPkg/DefaultExceptionHandlerLib: use console if available

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Wed, 26 Dec 2018 at 22:34, Laszlo Ersek <lersek@redhat.com> wrote:
>
> On 12/20/18 18:31, Ard Biesheuvel wrote:
> > Print the minimal 'exception occurred' message to the console instead
> > of straight to the serial port if the console is available. This makes
> > such messages visible on systems where the console is graphical and
> > the serial is not connected.
> >
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > ---
> >  ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c | 16 +++++++++++++---
> >  ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c     |  7 ++++++-
> >  ArmPkg/Library/DefaultExceptionHandlerLib/DefaultExceptionHandlerLib.inf    |  1 +
> >  3 files changed, 20 insertions(+), 4 deletions(-)
> >
> > diff --git a/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c b/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c
> > index 1024bf48c63d..1aaf3c88f21e 100644
> > --- a/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c
> > +++ b/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c
> > @@ -22,6 +22,7 @@
> >  #include <Library/PrintLib.h>
> >  #include <Library/ArmDisassemblerLib.h>
> >  #include <Library/SerialPortLib.h>
> > +#include <Library/UefiBootServicesTableLib.h>
> >
> >  #include <Guid/DebugImageInfoTable.h>
> >  #include <Protocol/DebugSupport.h>
> > @@ -159,14 +160,23 @@ DefaultExceptionHandler (
> >    INT32  Offset;
> >
> >    if (mRecursiveException) {
> > -    CharCount = AsciiSPrint (Buffer, sizeof (Buffer),"\nRecursive exception occurred while dumping the CPU state\n");
> > -    SerialPortWrite ((UINT8 *) Buffer, CharCount);
> > +    STATIC CHAR8 CONST Message[] = "\nRecursive exception occurred while dumping the CPU state\n";
> > +
> > +    if (gST->ConOut != NULL) {
> > +      AsciiPrint (Message);
> > +    } else {
> > +      SerialPortWrite ((UINT8 *)Message, AsciiStrLen (Message));
> > +    }
> >      CpuDeadLoop ();
> >    }
> >    mRecursiveException = TRUE;
> >
> >    CharCount = AsciiSPrint (Buffer,sizeof (Buffer),"\n\n%a Exception at 0x%016lx\n", gExceptionTypeString[ExceptionType], SystemContext.SystemContextAArch64->ELR);
> > -  SerialPortWrite ((UINT8 *) Buffer, CharCount);
> > +  if (gST->ConOut != NULL) {
> > +    AsciiPrint (Buffer);
> > +  } else {
> > +    SerialPortWrite ((UINT8 *)Buffer, CharCount);
> > +  }
> >
> >    DEBUG_CODE_BEGIN ();
> >      CHAR8  *Pdb, *PrevPdb;
> > diff --git a/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c b/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c
> > index 0b9da031b47d..9159b579da6f 100644
> > --- a/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c
> > +++ b/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c
> > @@ -21,6 +21,7 @@
> >  #include <Library/PrintLib.h>
> >  #include <Library/ArmDisassemblerLib.h>
> >  #include <Library/SerialPortLib.h>
> > +#include <Library/UefiBootServicesTableLib.h>
> >
> >  #include <Guid/DebugImageInfoTable.h>
> >
> > @@ -194,7 +195,11 @@ DefaultExceptionHandler (
> >
> >    CharCount = AsciiSPrint (Buffer,sizeof (Buffer),"\n%a Exception PC at 0x%08x  CPSR 0x%08x ",
> >           gExceptionTypeString[ExceptionType], SystemContext.SystemContextArm->PC, SystemContext.SystemContextArm->CPSR);
> > -  SerialPortWrite ((UINT8 *) Buffer, CharCount);
> > +  if (gST->ConOut != NULL) {
> > +    AsciiPrint (Buffer);
> > +  } else {
> > +    SerialPortWrite ((UINT8 *)Buffer, CharCount);
> > +  }
> >
> >    DEBUG_CODE_BEGIN ();
> >      CHAR8   *Pdb;
> > diff --git a/ArmPkg/Library/DefaultExceptionHandlerLib/DefaultExceptionHandlerLib.inf b/ArmPkg/Library/DefaultExceptionHandlerLib/DefaultExceptionHandlerLib.inf
> > index 7609f82d89a1..6bc48714c9dc 100644
> > --- a/ArmPkg/Library/DefaultExceptionHandlerLib/DefaultExceptionHandlerLib.inf
> > +++ b/ArmPkg/Library/DefaultExceptionHandlerLib/DefaultExceptionHandlerLib.inf
> > @@ -42,6 +42,7 @@
> >    PeCoffGetEntryPointLib
> >    ArmDisassemblerLib
> >    SerialPortLib
> > +  UefiBootServicesTableLib
> >
> >  [Guids]
> >    gEfiDebugImageInfoTableGuid
> >
>
> I feel that invoking such high level functionality from an exception
> handler is risky, but I do understand this is a last resort / best
> effort action, and if it *happens* to work on systems with no serial,
> then it's already a win.
>
> However, I'd suggest improving the robustness by preserving the serial
> write first, and then performing the (optional) console write in
> addition, second. I guess it can lead to the message appearing twice on
> serial (if the console is available, and it happens to be multiplexed to
> the serial port as well), but I think that's a better compromise than
> possibly losing the message altogether.
>
> I don't feel strongly about it either way, I just thought this worth
> raising.
>

Excellent point. I'll change this in v2