Re: [PATCH 2/2] ArmPkg/DefaultExceptionHandlerLib AARCH64: add minimal backtrace to crash dump

From: Michael Zimmermann <sigmaepsilon92@gmail.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: "edk2-devel@lists.01.org" <edk2-devel@lists.01.org>,
	Leif Lindholm <leif.lindholm@linaro.org>
Subject: Re: [PATCH 2/2] ArmPkg/DefaultExceptionHandlerLib AARCH64: add minimal backtrace to crash dump
Date: Wed, 7 Sep 2016 13:25:51 +0200	[thread overview]
Message-ID: <CAN9vWDK4u4uwR60C1DbzmrtFSz2GsoQKYWc5OJ98wUjqdq=fTw@mail.gmail.com> (raw)
In-Reply-To: <CAKv+Gu9B-2Emc2cXAEhT6AK5+5AasWwN6YJKiowVaUr8bDquoQ@mail.gmail.com>

> However, looking at this
> code, this is still not sufficient to find the *next* frame pointer on
> the stack.
are you sure about that? this code looks like it does just that:
https://github.com/torvalds/linux/blob/master/arch/arm/kernel/stacktrace.c

On Wed, Sep 7, 2016 at 1:03 PM, Ard Biesheuvel <ard.biesheuvel@linaro.org>
wrote:

> On 7 September 2016 at 10:48, Michael Zimmermann
> <sigmaepsilon92@gmail.com> wrote:
> > nice, can we do this for ARM too? I usually need to add DEBUG((...))'s
> all
> > over the place for hours until I found the reason for a fault.
> >
>
> This is going to be tricky. Unlike AARCH64, which unambiguously
> describes in the AAPCS how to link the stack frames using x29, the
> AAPCS for ARM does not standardise this, and so different compilers
> may do different things, also depending on whether you are executing
> in ARM or Thumb mode. For instance, the following prologue was snipped
> from a BdsDxe.dll build using GCC5 in Thumb2 mode.
>
> 00000254 <_ModuleEntryPoint>:
>      254:       e96d 7e02       strd    r7, lr, [sp, #-8]!
>      258:       b084            sub     sp, #16
>      25a:       af00            add     r7, sp, #0
>
> Googling around, i can indeed find sources that describe how GCC uses
> r7 as the frame pointer for Thumb2 code. However, looking at this
> code, this is still not sufficient to find the *next* frame pointer on
> the stack. IOW, there is no standardised layout to find the next frame
> pointer inside the stack frame.
>
> The only way to do this reliably is using unwind tables, but this is
> *much* more complicated than the 20 line patch that enables it for
> AArch64
>
> Ard.
>
>
> > On Wed, Sep 7, 2016 at 10:21 AM, Ard Biesheuvel <
> ard.biesheuvel@linaro.org>
> > wrote:
> >>
> >> When dumping the CPU state after an unhandled fault, walk the stack
> >> frames and decode the return addresses so we can show a minimal
> >> backtrace. Unfortunately, we do not have sufficient information to
> >> show the function names, but at least we can see the modules and the
> >> return addresses inside the modules.
> >>
> >> Contributed-under: TianoCore Contribution Agreement 1.0
> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> >> ---
> >>
> >> Example output:
> >>
> >> Synchronous Exception at 0x00000000F5EA4C8C
> >>
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_
> GCC5/AARCH64/ArmPlatformPkg/Drivers/NorFlashDxe/NorFlashDxe/DEBUG/
> ArmVeNorFlashDxe.dll
> >> loaded at 0x00000000F5E90000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_
> GCC5/AARCH64/ArmPlatformPkg/Drivers/NorFlashDxe/NorFlashDxe/DEBUG/
> ArmVeNorFlashDxe.dll
> >> (0x00000000F5EA4AE8) loaded at 0x00000000F5E90000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_
> GCC5/AARCH64/ArmPlatformPkg/Drivers/NorFlashDxe/NorFlashDxe/DEBUG/
> ArmVeNorFlashDxe.dll
> >> (0x00000000F5EA1BFC) loaded at 0x00000000F5E90000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_
> GCC5/AARCH64/ArmPlatformPkg/Drivers/NorFlashDxe/NorFlashDxe/DEBUG/
> ArmVeNorFlashDxe.dll
> >> (0x00000000F5EA23F4) loaded at 0x00000000F5E90000
> >> called from
> >> /work/jenkins/workspace/ap-uefi-bin/EDK2_ARCH/ARM/EDK2_
> BINARY/FatPkg/label/sas-sw/Build/Fat/RELEASE_GCC49/
> AARCH64/FatPkg/EnhancedFatDxe/Fat/DEBUG/Fat.dll
> >> (0x00000000FADC454C) loaded at 0x00000000FADC3000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_
> GCC5/AARCH64/MdeModulePkg/Core/Dxe/DxeMain/DEBUG/DxeCore.dll
> >> (0x00000000FE47C868) loaded at 0x00000000FE471000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_GCC5/AARCH64/
> IntelFrameworkModulePkg/Universal/BdsDxe/BdsDxe/DEBUG/BdsDxe.dll
> >> (0x00000000FAE2C50C) loaded at 0x00000000FAE01000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_GCC5/AARCH64/
> IntelFrameworkModulePkg/Universal/BdsDxe/BdsDxe/DEBUG/BdsDxe.dll
> >> (0x00000000FAE2C674) loaded at 0x00000000FAE01000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_GCC5/AARCH64/
> IntelFrameworkModulePkg/Universal/BdsDxe/BdsDxe/DEBUG/BdsDxe.dll
> >> (0x00000000FAE2C264) loaded at 0x00000000FAE01000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_GCC5/AARCH64/
> IntelFrameworkModulePkg/Universal/BdsDxe/BdsDxe/DEBUG/BdsDxe.dll
> >> (0x00000000FAE36998) loaded at 0x00000000FAE01000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_GCC5/AARCH64/
> IntelFrameworkModulePkg/Universal/BdsDxe/BdsDxe/DEBUG/BdsDxe.dll
> >> (0x00000000FAE03668) loaded at 0x00000000FAE01000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_
> GCC5/AARCH64/MdeModulePkg/Core/Dxe/DxeMain/DEBUG/DxeCore.dll
> >> (0x00000000FE4733F0) loaded at 0x00000000FE471000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_
> GCC5/AARCH64/MdeModulePkg/Core/Dxe/DxeMain/DEBUG/DxeCore.dll
> >> (0x00000000FE4724A0) loaded at 0x00000000FE471000
> >> called from
> >> /home/ard/build/edk2/Build/ArmVExpress-FVP-AArch64/DEBUG_
> GCC5/AARCH64/MdeModulePkg/Core/Dxe/DxeMain/DEBUG/DxeCore.dll
> >> (0x00000000FE472024) loaded at 0x00000000FE471000
> >> ---
> >>  .../AArch64/DefaultExceptionHandler.c               | 21
> >> +++++++++++++++++++++
> >>  1 file changed, 21 insertions(+)
> >>
> >> diff --git
> >> a/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/
> DefaultExceptionHandler.c
> >> b/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/
> DefaultExceptionHandler.c
> >> index 31fc936b21ff..84b442f2b6f4 100644
> >> ---
> >> a/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/
> DefaultExceptionHandler.c
> >> +++
> >> b/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/
> DefaultExceptionHandler.c
> >> @@ -152,9 +152,30 @@ DefaultExceptionHandler (
> >>      CHAR8  *Pdb;
> >>      UINTN  ImageBase;
> >>      UINTN  PeCoffSizeOfHeader;
> >> +    UINT64 *Fp;
> >> +
> >>      Pdb = GetImageName (SystemContext.SystemContextAArch64->ELR,
> >> &ImageBase, &PeCoffSizeOfHeader);
> >>      if (Pdb != NULL) {
> >>        DEBUG ((EFI_D_ERROR, "%a loaded at 0x%016lx \n", Pdb,
> ImageBase));
> >> +
> >> +      Pdb = GetImageName (SystemContext.SystemContextAArch64->LR,
> >> &ImageBase,
> >> +              &PeCoffSizeOfHeader);
> >> +      if (Pdb != NULL) {
> >> +        DEBUG ((EFI_D_ERROR, "called from %a (0x%016lx) loaded at
> >> 0x%016lx \n",
> >> +          Pdb, SystemContext.SystemContextAArch64->LR, ImageBase));
> >> +      }
> >> +      for (Fp = (UINT64 *)SystemContext.SystemContextAArch64->FP;
> >> +           *Fp != 0;
> >> +           Fp = (UINT64 *)Fp[0]) {
> >> +        if (Fp[1] == SystemContext.SystemContextAArch64->LR) {
> >> +         continue;
> >> +        }
> >> +        Pdb = GetImageName (Fp[1], &ImageBase, &PeCoffSizeOfHeader);
> >> +        if (Pdb != NULL) {
> >> +          DEBUG ((EFI_D_ERROR, "called from %a (0x%016lx) loaded at
> >> 0x%016lx \n",
> >> +            Pdb, Fp[1], ImageBase));
> >> +        }
> >> +      }
> >>      }
> >>    DEBUG_CODE_END ();
> >>
> >> --
> >> 2.7.4
> >>
> >> _______________________________________________
> >> edk2-devel mailing list
> >> edk2-devel@lists.01.org
> >> https://lists.01.org/mailman/listinfo/edk2-devel
> >
> >
>