Re: [RFC 1/1] UefiCpuPkg/CpuExceptionHandlerLib/X64: Add stack trace support

[Paulo Alcantara <pcacjr@zytor.com>]

Hi Andrew,

On 14/11/2017 12:01, Andrew Fish wrote:
C> Paulo,
> 
> Cool feature. How does this code deal with VC++ that code does not store the frame pointer and requires symbols to unwind.

I haven't tested in with MSVC, so I'd hope to get some help from Intel's 
guys to help supporting and testing it :-)

Regarding the symbols, I performed some tests by writing a userspace 
PE/COFF application [1] and tried to:

(a) handle the RUNTIME_FUNCTION entries in exception table (.pdata 
section) to find the function starting address and then its respective 
symbol name in COFF symbol table.

(b) Walk through UNWIND_INFO entries in .xdata section to figure out 
which CPU register a function used as a frame pointer or if it didn't 
use any at
all.

The problem I had with (a) was that the COFF symbol table is not mapped 
directory into the image's address space -- that is, the 
"PointerToSymbolTable" in File Header *should* be 0 as per PE/COFF 
format specific when handling an executable file rather a object file. 
Additionally, if it's non-zero, it contains a file offset rather than a 
RVA address, so impossible to parse it at runtime.

In (b), I realized that the CodeView format data in debug directory 
should be kept in a separate file (PDB file?) and they aren't mapped 
into image's address space as well.

I don't have so much experience with PE/COFF format, so please correct 
me if I'm mistaken.

IMHO, there should be exist a function like AsmGetFrameAddress() and/or 
AsmGetStackAddress() which would get implemented for both GCC and MSVC 
toolchains.

Thank you very much for your comments!

> Also on the page fault you can print the fault address since it is in CR2.

Good point! We should also do that.

> It should be possible to post process the text file and make a symbolicated backtrace.

Yes.

Thanks!
Paulo

> 
> Thanks,
> 
> Andrew Fish
> 
>> On Nov 14, 2017, at 4:47 AM, Paulo Alcantara <pcacjr@zytor.com> wrote:
>>
>> This patch adds stack trace support during a X64 CPU exception.
>>
>> It will dump out back trace, stack contents as well as image module
>> names that were part of the call stack.
>>
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Cc: Eric Dong <eric.dong@intel.com>
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> Signed-off-by: Paulo Alcantara <pcacjr@zytor.com>
>> ---
>> UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c | 344 +++++++++++++++++++-
>> 1 file changed, 342 insertions(+), 2 deletions(-)
>>
>> diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
>> index 65f0cff680..7048247be3 100644
>> --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
>> +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
>> @@ -14,6 +14,11 @@
>>
>> #include "CpuExceptionCommon.h"
>>
>> +//
>> +// Unknown PDB file name
>> +//
>> +GLOBAL_REMOVE_IF_UNREFERENCED CONST CHAR8 *mUnknownPdbFileName = "????";
>> +
>> /**
>>    Return address map of exception handler template so that C code can generate
>>    exception tables.
>> @@ -243,6 +248,325 @@ DumpCpuContext (
>> }
>>
>> /**
>> +  Dump stack contents.
>> +
>> +  @param[in]  ImageBase            Base address of PE/COFF image.
>> +  @param[out] PdbAbsoluteFilePath  Absolute path of PDB file.
>> +  @param[out] PdbFileName          File name of PDB file.
>> +**/
>> +STATIC
>> +VOID
>> +GetPdbFileName (
>> +  IN  UINTN    ImageBase,
>> +  OUT CHAR8    **PdbAbsoluteFilePath,
>> +  OUT CHAR8    **PdbFileName
>> +  )
>> +{
>> +  VOID   *PdbPointer;
>> +  CHAR8  *Str;
>> +
>> +  //
>> +  // Get PDB file name from PE/COFF image
>> +  //
>> +  PdbPointer = PeCoffLoaderGetPdbPointer ((VOID *)ImageBase);
>> +  if (PdbPointer == NULL) {
>> +    //
>> +    // No PDB file name found. Set it to an unknown file name.
>> +    //
>> +    *PdbFileName = (CHAR8 *)mUnknownPdbFileName;
>> +    if (PdbAbsoluteFilePath != NULL) {
>> +      *PdbAbsoluteFilePath = NULL;
>> +    }
>> +  } else {
>> +    //
>> +    // Get file name portion out of PDB file in PE/COFF image
>> +    //
>> +    Str = (CHAR8 *)((UINTN)PdbPointer +
>> +                    AsciiStrLen ((CHAR8 *)PdbPointer) - sizeof *Str);
>> +    for (; *Str != '/' && *Str != '\\'; Str--) {
>> +      ;
>> +    }
>> +
>> +    //
>> +    // Set PDB file name (also skip trailing path separator: '/' or '\\')
>> +    //
>> +    *PdbFileName = Str + 1;
>> +
>> +    if (PdbAbsoluteFilePath != NULL) {
>> +      //
>> +      // Set absolute file path of PDB file
>> +      //
>> +      *PdbAbsoluteFilePath = PdbPointer;
>> +    }
>> +  }
>> +}
>> +
>> +/**
>> +  Dump stack contents.
>> +
>> +  @param[in]  CurrentRsp         Current stack pointer address.
>> +  @param[in]  UnwondStacksCount  Count of unwond stack frames.
>> +**/
>> +STATIC
>> +VOID
>> +DumpStackContents (
>> +  IN UINT64  CurrentRsp,
>> +  IN INTN    UnwondStacksCount
>> +  )
>> +{
>> +  if (UnwondStacksCount == 0) {
>> +    return;
>> +  }
>> +
>> +  //
>> +  // Dump out stack contents
>> +  //
>> +  InternalPrintMessage ("\nStack dump:\n");
>> +  while (UnwondStacksCount-- > 0) {
>> +    InternalPrintMessage (
>> +      "0x%016lx: %016lx %016lx\n",
>> +      CurrentRsp,
>> +      *(UINT64 *)CurrentRsp,
>> +      *(UINT64 *)((UINTN)CurrentRsp + 8)
>> +      );
>> +
>> +    //
>> +    // As per Microsoft x64 ABI, the stack pointer must be aligned on a 16 byte
>> +    // boundary.
>> +    //
>> +    CurrentRsp = CurrentRsp + 16;
>> +  }
>> +}
>> +
>> +/**
>> +  Dump all image module names from call stack.
>> +
>> +  @param[in]  SystemContext  Pointer to EFI_SYSTEM_CONTEXT.
>> +**/
>> +STATIC
>> +VOID
>> +DumpImageModuleNames (
>> +  IN EFI_SYSTEM_CONTEXT   SystemContext
>> +  )
>> +{
>> +  EFI_STATUS  Status;
>> +  UINT64      Rip;
>> +  UINTN       ImageBase;
>> +  VOID        *EntryPoint;
>> +  CHAR8       *PdbAbsoluteFilePath;
>> +  CHAR8       *PdbFileName;
>> +  UINT64      Rbp;
>> +
>> +  //
>> +  // Set current RIP address
>> +  //
>> +  Rip = SystemContext.SystemContextX64->Rip;
>> +
>> +  //
>> +  // Set current frame pointer address
>> +  //
>> +  Rbp = SystemContext.SystemContextX64->Rbp;
>> +
>> +  //
>> +  // Get initial PE/COFF image base address from current RIP
>> +  //
>> +  ImageBase = PeCoffSearchImageBase (Rip);
>> +  if (ImageBase == 0) {
>> +    InternalPrintMessage ("!!!! Could not find image module names. !!!!");
>> +    return;
>> +  }
>> +
>> +  //
>> +  // Get initial PE/COFF image's entry point
>> +  //
>> +  Status = PeCoffLoaderGetEntryPoint ((VOID *)ImageBase, &EntryPoint);
>> +  if (EFI_ERROR (Status)) {
>> +    EntryPoint = NULL;
>> +  }
>> +
>> +  //
>> +  // Get file name and absolute path of initial PDB file
>> +  //
>> +  GetPdbFileName (ImageBase, &PdbAbsoluteFilePath, &PdbFileName);
>> +
>> +  //
>> +  // Print out initial image module name (if any)
>> +  //
>> +  if (PdbAbsoluteFilePath != NULL) {
>> +    InternalPrintMessage (
>> +      "\n%a (ImageBase=0x%016lx, EntryPoint=0x%016lx):\n",
>> +      PdbFileName,
>> +      ImageBase,
>> +      (UINTN)EntryPoint
>> +      );
>> +    InternalPrintMessage ("%a\n", PdbAbsoluteFilePath);
>> +  }
>> +
>> +  //
>> +  // Walk through call stack and find next module names
>> +  //
>> +  for (;;) {
>> +    //
>> +    // Set RIP with return address from current stack frame
>> +    //
>> +    Rip = *(UINT64 *)((UINTN)Rbp + 8);
>> +
>> +    //
>> +    // Check if RIP is within another PE/COFF image base address
>> +    //
>> +    if (Rip < ImageBase) {
>> +      //
>> +      // Search for the respective PE/COFF image based on RIP
>> +      //
>> +      ImageBase = PeCoffSearchImageBase (Rip);
>> +      if (ImageBase == 0) {
>> +        //
>> +        // Stop stack trace
>> +        //
>> +        break;
>> +      }
>> +
>> +      //
>> +      // Get PE/COFF image's entry point
>> +      //
>> +      Status = PeCoffLoaderGetEntryPoint ((VOID *)ImageBase, &EntryPoint);
>> +      if (EFI_ERROR (Status)) {
>> +        EntryPoint = NULL;
>> +      }
>> +
>> +      //
>> +      // Get file name and absolute path of PDB file
>> +      //
>> +      GetPdbFileName (ImageBase, &PdbAbsoluteFilePath, &PdbFileName);
>> +
>> +      //
>> +      // Print out image module name (if any)
>> +      //
>> +      if (PdbAbsoluteFilePath != NULL) {
>> +        InternalPrintMessage (
>> +          "%a (ImageBase=0x%016lx, EntryPoint=0x%016lx):\n",
>> +          PdbFileName,
>> +          ImageBase,
>> +          (UINTN)EntryPoint
>> +          );
>> +        InternalPrintMessage ("%a\n", PdbAbsoluteFilePath);
>> +      }
>> +    }
>> +
>> +    //
>> +    // Unwind the stack
>> +    //
>> +    Rbp = *(UINT64 *)(UINTN)Rbp;
>> +  }
>> +}
>> +
>> +/**
>> +  Dump stack trace.
>> +
>> +  @param[in]  SystemContext      Pointer to EFI_SYSTEM_CONTEXT.
>> +  @param[out] UnwondStacksCount  Count of unwond stack frames.
>> +**/
>> +STATIC
>> +VOID
>> +DumpStackTrace (
>> +  IN  EFI_SYSTEM_CONTEXT   SystemContext,
>> +  OUT INTN                 *UnwondStacksCount
>> +  )
>> +{
>> +  UINT64  Rip;
>> +  UINT64  Rbp;
>> +  UINTN   ImageBase;
>> +  CHAR8   *PdbFileName;
>> +
>> +  //
>> +  // Initialize count of unwond stacks
>> +  //
>> +  *UnwondStacksCount = 0;
>> +
>> +  //
>> +  // Set current RIP address
>> +  //
>> +  Rip = SystemContext.SystemContextX64->Rip;
>> +
>> +  //
>> +  // Set current frame pointer address
>> +  //
>> +  Rbp = SystemContext.SystemContextX64->Rbp;
>> +
>> +  //
>> +  // Get initial PE/COFF image base address from current RIP
>> +  //
>> +  ImageBase = PeCoffSearchImageBase (Rip);
>> +  if (ImageBase == 0) {
>> +    InternalPrintMessage ("!!!! Could not find backtrace information. !!!!");
>> +    return;
>> +  }
>> +
>> +  //
>> +  // Get PDB file name from initial PE/COFF image
>> +  //
>> +  GetPdbFileName (ImageBase, NULL, &PdbFileName);
>> +
>> +  //
>> +  // Print out back trace
>> +  //
>> +  InternalPrintMessage ("\nBack trace:\n");
>> +
>> +  for (;;) {
>> +    //
>> +    // Print stack frame in the following format:
>> +    //
>> +    // # <RIP> @ <ImageBase>+<RelOffset> (RBP) in [<ModuleName> | ????]
>> +    //
>> +    InternalPrintMessage (
>> +      "%d 0x%016lx @ 0x%016lx+0x%x (0x%016lx) in %a\n",
>> +      *UnwondStacksCount,
>> +      Rip,
>> +      ImageBase,
>> +      Rip - ImageBase - 1,
>> +      Rbp,
>> +      PdbFileName
>> +      );
>> +
>> +    //
>> +    // Set RIP with return address from current stack frame
>> +    //
>> +    Rip = *(UINT64 *)((UINTN)Rbp + 8);
>> +
>> +    //
>> +    // Check if RIP is within another PE/COFF image base address
>> +    //
>> +    if (Rip < ImageBase) {
>> +      //
>> +      // Search for the respective PE/COFF image based on RIP
>> +      //
>> +      ImageBase = PeCoffSearchImageBase (Rip);
>> +      if (ImageBase == 0) {
>> +        //
>> +        // Stop stack trace
>> +        //
>> +        break;
>> +      }
>> +
>> +      //
>> +      // Get PDB file name
>> +      //
>> +      GetPdbFileName (ImageBase, NULL, &PdbFileName);
>> +    }
>> +
>> +    //
>> +    // Unwind the stack
>> +    //
>> +    Rbp = *(UINT64 *)(UINTN)Rbp;
>> +
>> +    //
>> +    // Increment count of unwond stacks
>> +    //
>> +    (*UnwondStacksCount)++;
>> +  }
>> +}
>> +
>> +/**
>>    Display CPU information.
>>
>>    @param ExceptionType  Exception type.
>> @@ -254,9 +578,25 @@ DumpImageAndCpuContent (
>>    IN EFI_SYSTEM_CONTEXT   SystemContext
>>    )
>> {
>> +  INTN UnwondStacksCount;
>> +
>> +  //
>> +  // Dump CPU context
>> +  //
>>    DumpCpuContext (ExceptionType, SystemContext);
>> +
>> +  //
>> +  // Dump stack trace
>> +  //
>> +  DumpStackTrace (SystemContext, &UnwondStacksCount);
>> +
>> +  //
>> +  // Dump image module names
>> +  //
>> +  DumpImageModuleNames (SystemContext);
>> +
>>    //
>> -  // Dump module image base and module entry point by RIP
>> +  // Dump stack contents
>>    //
>> -  DumpModuleImageInfo (SystemContext.SystemContextX64->Rip);
>> +  DumpStackContents (SystemContext.SystemContextX64->Rsp, UnwondStacksCount);
>> }
>> -- 
>> 2.11.0
>>
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