[LLDB] Use r11 as frame pointer on Windows on ARM

[labath]

Presumably, this should change how unwind plans are computed. The unwind machinery will treat a mov %sp, %fp(whatever is the arm equivalent) as a signal that it should switch to an frame-pointer based unwind. This logic should not kick in if lldb does not think this register is the frame pointer register. You should be able to check this via image show-unwind. If that shows some difference then it should be possible to concoct a function where the unwind goes wrong because of this, but that's not necessary -- it should be enough to just check that a reasonable unwind plan is generated.

[mstorsjo]

Added a testcase using a minidump. I had to add recognition of r11 as a potential frame pointer register in thumb mode in the handling of one instruction, to make it pick up the exact form my testcase happened to use. There's potentially other cases also where the thumb emulation doesn't expect r11 to be a frame pointer, but this at least verifies the change to GetFramePointerRegisterNumber.

lldb/source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp

// NEED_BRIDGEOS_TRIPLE case llvm::Triple::BridgeOS:
     is_apple = true;
     break;
   default:
     break;
   }
 
   /* On Apple iOS et al, the frame pointer register is always r7.
    * Typically on other ARM systems, thumb code uses r7; arm code uses r11.
+   * Windows on ARM, which is in thumb mode, uses r11 though.
    */
 
   uint32_t fp_regnum = 11;
 
   if (is_apple)
     fp_regnum = 7;
 
-  if (m_opcode_mode == eModeThumb)
+  if (m_opcode_mode == eModeThumb && !m_arch.GetTriple().isOSWindows())
     fp_regnum = 7;
 
   return fp_regnum;
 }
 
 uint32_t EmulateInstructionARM::GetFramePointerDWARFRegisterNumber() const {
   bool is_apple = false;
   if (m_arch.GetTriple().getVendor() == llvm::Triple::Apple)
     is_apple = true;
   switch (m_arch.GetTriple().getOS()) {
   case llvm::Triple::Darwin:
   case llvm::Triple::MacOSX:
   case llvm::Triple::IOS:
     is_apple = true;
     break;
   default:
     break;
   }
 
   /* On Apple iOS et al, the frame pointer register is always r7.
    * Typically on other ARM systems, thumb code uses r7; arm code uses r11.
+   * Windows on ARM, which is in thumb mode, uses r11 though.
    */
 
   uint32_t fp_regnum = dwarf_r11;
 
   if (is_apple)
     fp_regnum = dwarf_r7;
 
-  if (m_opcode_mode == eModeThumb)
+  if (m_opcode_mode == eModeThumb && !m_arch.GetTriple().isOSWindows())
     fp_regnum = dwarf_r7;
 
   return fp_regnum;
 }
 
 // Push Multiple Registers stores multiple registers to the stack, storing to
 // consecutive memory locations ending just below the address in SP, and
 // updates
if (ConditionPassed(opcode)) {
     uint32_t result = ReadCoreReg(Rm, &success);
     if (!success)
       return false;
 
     // The context specifies that Rm is to be moved into Rd.
     EmulateInstruction::Context context;
     if (Rd == 13)
       context.type = EmulateInstruction::eContextAdjustStackPointer;
+    else if (Rd == GetFramePointerRegisterNumber() && Rm == 13)
+      context.type = EmulateInstruction::eContextSetFramePointer;
     else
       context.type = EmulateInstruction::eContextRegisterPlusOffset;
     RegisterInfo dwarf_reg;
     GetRegisterInfo(eRegisterKindDWARF, dwarf_r0 + Rm, dwarf_reg);
     context.SetRegisterPlusOffset(dwarf_reg, 0);
 
     if (!WriteCoreRegOptionalFlags(context, result, Rd, setflags))
       return false;

lldb/test/Shell/Minidump/Windows/Inputs/arm-fp-unwind.dmp.yaml

+--- !minidump
+Version:         0xA0BAA793
+Flags:           0x0000000000000800
+Streams:
+  - Type:            ThreadList
+    Threads:
+      - Thread Id:       0x00004034
+        Suspend Count:   0x00000001
+        Priority Class:  0x00000020
+        Environment Block: 0x00000000007E6000
+        Context:         0000000000000000
+        Stack:
+          Start of Memory Range: 0x00000000008FF758
+          Content:         00000000000000
+  - Type:            ModuleList
+    Modules:
+      - Base of Image:   0x0000000000C70000
+        Size of Image:   0x00002000
+        Time Date Stamp: 1574942531
+        Module Name:     'arm-fp-unwind.exe'
+        CodeView Record: ''
+        Reserved0:       0x0000000000008140
+  - Type:            SystemInfo
+    Processor Arch:  ARM
+    Processor Level: 2049
+    Processor Revision: 2564
+    Number of Processors: 8
+    Product type:    1
+    Major Version:   10
+    Build Number:    18362
+    Platform ID:     Win32NT
+    Suite Mask:      0x0100
+    CPU:
+      CPUID:           0xEB8C1004
+  - Type:            MiscInfo
+    Content:         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
+...

lldb/test/Shell/Minidump/Windows/Inputs/arm-fp-unwind.exe.yaml

+--- !COFF
+OptionalHeader:
+  AddressOfEntryPoint: 4097
+  ImageBase:       4194304
+  SectionAlignment: 4096
+  FileAlignment:   512
+  MajorOperatingSystemVersion: 6
+  MinorOperatingSystemVersion: 0
+  MajorImageVersion: 0
+  MinorImageVersion: 0
+  MajorSubsystemVersion: 6
+  MinorSubsystemVersion: 0
+  Subsystem:       IMAGE_SUBSYSTEM_WINDOWS_CUI
+  DLLCharacteristics: [ IMAGE_DLL_CHARACTERISTICS_DYNAMIC_BASE, IMAGE_DLL_CHARACTERISTICS_NX_COMPAT, IMAGE_DLL_CHARACTERISTICS_TERMINAL_SERVER_AWARE ]
+  SizeOfStackReserve: 1048576
+  SizeOfStackCommit: 4096
+  SizeOfHeapReserve: 1048576
+  SizeOfHeapCommit: 4096
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+    Size:            0
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+    Size:            0
+  GlobalPtr:
+    RelativeVirtualAddress: 0
+    Size:            0
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+    Size:            0
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+    Size:            0
+  DelayImportDescriptor:
+    RelativeVirtualAddress: 0
+    Size:            0
+  ClrRuntimeHeader:
+    RelativeVirtualAddress: 0
+    Size:            0
+header:
+  Machine:         IMAGE_FILE_MACHINE_ARMNT
+  Characteristics: [ IMAGE_FILE_EXECUTABLE_IMAGE, IMAGE_FILE_32BIT_MACHINE ]
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    VirtualAddress:  4096
+    VirtualSize:     38
+    SectionData:     2DE90048EB46ADF5007D684600F004F80DF5007DBDE8008800BE01784278415C805C08447047
+symbols:
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+    StorageClass:    IMAGE_SYM_CLASS_STATIC
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+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            other
+    Value:           24
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...

lldb/test/Shell/Minidump/Windows/arm-fp-unwind.test

+Test that unwind plans use the frame pointer register correctly.
+
+REQUIRES: arm
+
+RUN: yaml2obj %S/Inputs/arm-fp-unwind.exe.yaml > %T/arm-fp-unwind.exe
+RUN: yaml2obj %S/Inputs/arm-fp-unwind.dmp.yaml > %T/arm-fp-unwind.dmp
+RUN: %lldb -O "settings set target.exec-search-paths %T" \
+RUN:   -c %T/arm-fp-unwind.dmp -o "image show-unwind -a 0x00c71010" -b \
+RUN:   | FileCheck %s
+
+CHECK: Assembly language inspection UnwindPlan:
+CHECK-NEXT: This UnwindPlan originally sourced from EmulateInstructionARM
+CHECK-NEXT: This UnwindPlan is sourced from the compiler: no.
+CHECK-NEXT: This UnwindPlan is valid at all instruction locations: yes.
+CHECK-NEXT: row[0]:    0: CFA=sp +0 =>
+CHECK-NEXT: row[1]:    4: CFA=sp +8 => fp=[CFA-8] lr=[CFA-4]
+CHECK-NEXT: row[2]:    6: CFA=fp +8 => fp=[CFA-8] lr=[CFA-4]