[llvm-objdump] Add simple memory expressions to variable display

[ostannard]

Summary

This adds the DW_OP_breg0..DW_OP_breg31 and DW_OP_bregx opcodes to the DWARF expression printer, so we can display locations for source variables which are in memory.

[aprantl]

llvm/test/tools/llvm-objdump/ARM/debug-vars-breg.s

1

Same comment as applies as in the other review. Could this be tested with a unittest that just dumps a single expression?

[ostannard]

Convert expression printing test to unit tests. Thanks for the suggestion, this is a much neater way to test this.

llvm/lib/DebugInfo/DWARF/DWARFExpression.cpp

case dwarf::DW_OP_regx: {
       if (!LLVMRegNum) {
         OS << "<unknown register " << DwarfRegNum << ">";
         return false;
       }
       raw_svector_ostream S(Stack.emplace_back(PrintedExpr::Value).String);
       S << MRI->getName(*LLVMRegNum);
       break;
     }
+    case dwarf::DW_OP_bregx: {
+      int DwarfRegNum = Op.getRawOperand(0);
+      int64_t Offset = Op.getRawOperand(1);
+      Optional<unsigned> LLVMRegNum = MRI->getLLVMRegNum(DwarfRegNum, false);
+      if (!LLVMRegNum) {
+        OS << "<unknown register " << DwarfRegNum << ">";
+        return false;
+      }
+      raw_svector_ostream S(Stack.emplace_back().String);
+      S << MRI->getName(*LLVMRegNum);
+      if (Offset)
+        S << format("%+" PRId64, Offset);
+      break;
+    }
     default:
       if (Opcode >= dwarf::DW_OP_reg0 && Opcode <= dwarf::DW_OP_reg31) {
         uint64_t DwarfRegNum = Opcode - dwarf::DW_OP_reg0;
         Optional<unsigned> LLVMRegNum = MRI->getLLVMRegNum(DwarfRegNum, false);
         if (!LLVMRegNum) {
           OS << "<unknown register " << DwarfRegNum << ">";
           return false;
         }
         raw_svector_ostream S(Stack.emplace_back(PrintedExpr::Value).String);
         S << MRI->getName(*LLVMRegNum);
+      } else if (Opcode >= dwarf::DW_OP_breg0 &&
+                 Opcode <= dwarf::DW_OP_breg31) {
+        int DwarfRegNum = Opcode - dwarf::DW_OP_breg0;
+        int64_t Offset = Op.getRawOperand(0);
+        Optional<unsigned> LLVMRegNum = MRI->getLLVMRegNum(DwarfRegNum, false);
+        if (!LLVMRegNum) {
+          OS << "<unknown register " << DwarfRegNum << ">";
+          return false;
+        }
+        raw_svector_ostream S(Stack.emplace_back().String);
+        S << MRI->getName(*LLVMRegNum);
+        if (Offset)
+          S << format("%+" PRId64, Offset);
       } else {
         // If we hit an unknown operand, we don't know its effect on the stack,
         // so bail out on the whole expression.
         OS << "<unknown op " << dwarf::OperationEncodingString(Opcode) << " ("
            << (int)Opcode << ")>";
         return false;
       }
       break;
     }
     ++I;
   }
 
   assert(Stack.size() == 1 && "expected one value on stack");
+
+  if (Stack.front().Kind == PrintedExpr::Address)
+    OS << "[" << Stack.front().String << "]";
+  else
     OS << Stack.front().String;
 
   return true;
 }
 
 bool DWARFExpression::prettyPrint(raw_ostream &OS, const MCRegisterInfo *MRI) {
   return prettyPrintDWARFExpr(OS, begin(), end(), MRI);
 }
 
 } // namespace llvm

llvm/test/tools/llvm-objdump/ARM/debug-vars-breg.s

+# RUN: llvm-mc --triple armv8a--none-eabi < %s --filetype=obj | \
+# RUN:     llvm-objdump - -d --debug-vars --no-show-raw-insn | \
+# RUN:     FileCheck %s
+
+## Check that the --debug-vars option works for memory locations using the
+## DW_OP_breg<N> opcodes.
+
+## Generated with this compile command and source code:
+## clang --target=arm--none-eabi -march=armv7-a -c debug.c -O1 -g -S -o -
+
+## void bar(int*);
+## void foo(int a) {
+##   bar(&a);
+## }
+
+# CHECK: Disassembly of section .text:
+# CHECK-EMPTY:
+# CHECK-NEXT: 00000000 foo:
+# CHECK-NEXT:                                                                   ┠─ a = R0
+# CHECK-NEXT:        0:       push    {r11, lr}                                 ┃
+# CHECK-NEXT:        4:       mov     r11, sp                                   ┃
+# CHECK-NEXT:        8:       sub     sp, sp, #8                                ┃
+# CHECK-NEXT:                                                                   ┃ ┌─ a = [SP+4]
+# CHECK-NEXT:        c:       str     r0, [sp, #4]                              ┻ ╈
+# CHECK-NEXT:       10:       add     r0, sp, #4                                  ┃
+# CHECK-NEXT:       14:       bl      #-8 <foo+0x14>                              ┃
+# CHECK-NEXT:       18:       mov     sp, r11                                     ┻
+# CHECK-NEXT:       1c:       pop     {r11, pc}
+
+
+  .text
+  .syntax unified
+  .eabi_attribute 67, "2.09"
+  .eabi_attribute 6, 10
+  .eabi_attribute 7, 65
+  .eabi_attribute 8, 1
+  .eabi_attribute 9, 2
+  .fpu  neon
+  .eabi_attribute 34, 0
+  .eabi_attribute 17, 1
+  .eabi_attribute 20, 1
+  .eabi_attribute 21, 1
+  .eabi_attribute 23, 3
+  .eabi_attribute 24, 1
+  .eabi_attribute 25, 1
+  .eabi_attribute 38, 1
+  .eabi_attribute 18, 4
+  .eabi_attribute 26, 2
+  .eabi_attribute 14, 0
+  .file "debug.c"
+  .file 1 "/work/scratch" "debug.c"
+  .globl  foo
+  .p2align  2
+  .type foo,%function
+  .code 32
+foo:
+.Lfunc_begin0:
+  .loc  1 2 0
+  .fnstart
+  .cfi_sections .debug_frame
+  .cfi_startproc
+  .save {r11, lr}
+  push  {r11, lr}
+  .cfi_def_cfa_offset 8
+  .cfi_offset lr, -4
+  .cfi_offset r11, -8
+  .setfp  r11, sp
+  mov r11, sp
+  .cfi_def_cfa_register r11
+  .pad  #8
+  sub sp, sp, #8
+  str r0, [sp, #4]
+.Ltmp0:
+  add r0, sp, #4
+.Ltmp1:
+  .loc  1 3 3 prologue_end
+  bl  bar
+.Ltmp2:
+  .loc  1 4 1
+  mov sp, r11
+.Ltmp3:
+  pop {r11, pc}
+.Ltmp4:
+.Lfunc_end0:
+  .size foo, .Lfunc_end0-foo
+  .cfi_endproc
+  .cantunwind
+  .fnend
+
+  .section  .debug_str,"MS",%progbits,1
+.Linfo_string0:
+  .asciz  "clang version 10.0.0 ([e-mail]:llvm/llvm-project.git e73f78acd34360f7450b81167d9dc858ccddc262)"
+.Linfo_string1:
+  .asciz  "debug.c"
+.Linfo_string2:
+  .asciz  "/work/scratch"
+.Linfo_string3:
+  .asciz  "bar"
+.Linfo_string4:
+  .asciz  "int"
+.Linfo_string5:
+  .asciz  "foo"
+.Linfo_string6:
+  .asciz  "a"
+  .section  .debug_loc,"",%progbits
+.Ldebug_loc0:
+  .long .Lfunc_begin0-.Lfunc_begin0
+  .long .Ltmp0-.Lfunc_begin0
+  .short  1
+  .byte 80
+  .long .Ltmp0-.Lfunc_begin0
+  .long .Ltmp3-.Lfunc_begin0
+  .short  2
+  .byte 125
+  .byte 4
+  .long 0
+  .long 0
+  .section  .debug_abbrev,"",%progbits
+  .byte 1
+  .byte 17
+  .byte 1
+  .byte 37
+  .byte 14
+  .byte 19
+  .byte 5
+  .byte 3
+  .byte 14
+  .byte 16
+  .byte 23
+  .byte 27
+  .byte 14
+  .byte 17
+  .byte 1
+  .byte 18
+  .byte 6
+  .byte 0
+  .byte 0
+  .byte 2
+  .byte 46
+  .byte 1
+  .byte 3
+  .byte 14
+  .byte 58
+  .byte 11
+  .byte 59
+  .byte 11
+  .byte 39
+  .byte 25
+  .byte 60
+  .byte 25
+  .byte 63
+  .byte 25
+  .byte 0
+  .byte 0
+  .byte 3
+  .byte 5
+  .byte 0
+  .byte 73
+  .byte 19
+  .byte 0
+  .byte 0
+  .byte 4
+  .byte 15
+  .byte 0
+  .byte 73
+  .byte 19
+  .byte 0
+  .byte 0
+  .byte 5
+  .byte 36
+  .byte 0
+  .byte 3
+  .byte 14
+  .byte 62
+  .byte 11
+  .byte 11
+  .byte 11
+  .byte 0
+  .byte 0
+  .byte 6
+  .byte 46
+  .byte 1
+  .byte 17
+  .byte 1
+  .byte 18
+  .byte 6
+  .byte 64
+  .byte 24
+  .ascii  "\227B"
+  .byte 25
+  .byte 3
+  .byte 14
+  .byte 58
+  .byte 11
+  .byte 59
+  .byte 11
+  .byte 39
+  .byte 25
+  .byte 63
+  .byte 25
+  .byte 0
+  .byte 0
+  .byte 7
+  .byte 5
+  .byte 0
+  .byte 2
+  .byte 23
+  .byte 3
+  .byte 14
+  .byte 58
+  .byte 11
+  .byte 59
+  .byte 11
+  .byte 73
+  .byte 19
+  .byte 0
+  .byte 0
+  .byte 8
+  .ascii  "\211\202\001"
+  .byte 0
+  .byte 49
+  .byte 19
+  .byte 17
+  .byte 1
+  .byte 0
+  .byte 0
+  .byte 0
+  .section  .debug_info,"",%progbits
+.Lcu_begin0:
+  .long .Ldebug_info_end0-.Ldebug_info_start0
+.Ldebug_info_start0:
+  .short  4
+  .long .debug_abbrev
+  .byte 4
+  .byte 1
+  .long .Linfo_string0
+  .short  12
+  .long .Linfo_string1
+  .long .Lline_table_start0
+  .long .Linfo_string2
+  .long .Lfunc_begin0
+  .long .Lfunc_end0-.Lfunc_begin0
+  .byte 2
+  .long .Linfo_string3
+  .byte 1
+  .byte 1
+
+
+
+  .byte 3
+  .long 51
+  .byte 0
+  .byte 4
+  .long 56
+  .byte 5
+  .long .Linfo_string4
+  .byte 5
+  .byte 4
+  .byte 6
+  .long .Lfunc_begin0
+  .long .Lfunc_end0-.Lfunc_begin0
+  .byte 1
+  .byte 91
+
+  .long .Linfo_string5
+  .byte 1
+  .byte 2
+
+
+  .byte 7
+  .long .Ldebug_loc0
+  .long .Linfo_string6
+  .byte 1
+  .byte 2
+  .long 56
+  .byte 8
+  .long 38
+  .long .Ltmp2
+  .byte 0
+  .byte 0
+.Ldebug_info_end0:
+  .ident  "clang version 10.0.0 ([e-mail]:llvm/llvm-project.git e73f78acd34360f7450b81167d9dc858ccddc262)"
+  .section  ".note.GNU-stack","",%progbits
+  .addrsig
+  .eabi_attribute 30, 1
+  .section  .debug_line,"",%progbits
+.Lline_table_start0:

llvm/test/tools/llvm-objdump/ARM/debug-vars-bregx.s

+# RUN: llvm-mc --triple armv8a--none-eabi < %s --filetype=obj | \
+# RUN:     llvm-objdump - -d --debug-vars --no-show-raw-insn | \
+# RUN:     FileCheck %s
+
+## Check that the --debug-vars option works for memory locations using the
+## DW_OP_bregx opcode.
+
+## Generated with this compile command and source code, then modified to use
+## DW_OP_bregx instead of DW_OP_breg13:
+## clang --target=arm--none-eabi -march=armv7-a -c debug.c -O1 -g -S -o -
+
+## void bar(int*);
+## void foo(int a) {
+##   bar(&a);
+## }
+
+# CHECK: Disassembly of section .text:
+# CHECK-EMPTY:
+# CHECK-NEXT: 00000000 foo:
+# CHECK-NEXT:                                                                   ┠─ a = R0
+# CHECK-NEXT:        0:       push    {r11, lr}                                 ┃
+# CHECK-NEXT:        4:       mov     r11, sp                                   ┃
+# CHECK-NEXT:        8:       sub     sp, sp, #8                                ┃
+# CHECK-NEXT:                                                                   ┃ ┌─ a = [SP+4]
+# CHECK-NEXT:        c:       str     r0, [sp, #4]                              ┻ ╈
+# CHECK-NEXT:       10:       add     r0, sp, #4                                  ┃
+# CHECK-NEXT:       14:       bl      #-8 <foo+0x14>                              ┃
+# CHECK-NEXT:       18:       mov     sp, r11                                     ┻
+# CHECK-NEXT:       1c:       pop     {r11, pc}
+
+
+  .text
+  .syntax unified
+  .eabi_attribute 67, "2.09"
+  .eabi_attribute 6, 10
+  .eabi_attribute 7, 65
+  .eabi_attribute 8, 1
+  .eabi_attribute 9, 2
+  .fpu  neon
+  .eabi_attribute 34, 0
+  .eabi_attribute 17, 1
+  .eabi_attribute 20, 1
+  .eabi_attribute 21, 1
+  .eabi_attribute 23, 3
+  .eabi_attribute 24, 1
+  .eabi_attribute 25, 1
+  .eabi_attribute 38, 1
+  .eabi_attribute 18, 4
+  .eabi_attribute 26, 2
+  .eabi_attribute 14, 0
+  .file "debug.c"
+  .file 1 "/work/scratch" "debug.c"
+  .globl  foo
+  .p2align  2
+  .type foo,%function
+  .code 32
+foo:
+.Lfunc_begin0:
+  .loc  1 2 0
+  .fnstart
+  .cfi_sections .debug_frame
+  .cfi_startproc
+  .save {r11, lr}
+  push  {r11, lr}
+  .cfi_def_cfa_offset 8
+  .cfi_offset lr, -4
+  .cfi_offset r11, -8
+  .setfp  r11, sp
+  mov r11, sp
+  .cfi_def_cfa_register r11
+  .pad  #8
+  sub sp, sp, #8
+  str r0, [sp, #4]
+.Ltmp0:
+  add r0, sp, #4
+.Ltmp1:
+  .loc  1 3 3 prologue_end
+  bl  bar
+.Ltmp2:
+  .loc  1 4 1
+  mov sp, r11
+.Ltmp3:
+  pop {r11, pc}
+.Ltmp4:
+.Lfunc_end0:
+  .size foo, .Lfunc_end0-foo
+  .cfi_endproc
+  .cantunwind
+  .fnend
+
+  .section  .debug_str,"MS",%progbits,1
+.Linfo_string0:
+  .asciz  "clang version 10.0.0 ([e-mail]:llvm/llvm-project.git e73f78acd34360f7450b81167d9dc858ccddc262)"
+.Linfo_string1:
+  .asciz  "debug.c"
+.Linfo_string2:
+  .asciz  "/work/scratch"
+.Linfo_string3:
+  .asciz  "bar"
+.Linfo_string4:
+  .asciz  "int"
+.Linfo_string5:
+  .asciz  "foo"
+.Linfo_string6:
+  .asciz  "a"
+  .section  .debug_loc,"",%progbits
+.Ldebug_loc0:
+  .long .Lfunc_begin0-.Lfunc_begin0
+  .long .Ltmp0-.Lfunc_begin0
+  .short  1
+  .byte 80
+  .long .Ltmp0-.Lfunc_begin0
+  .long .Ltmp3-.Lfunc_begin0
+  // Modified debug info:
+  .short  3   // Expr length 3 bytes
+  .byte 0x92  // DW_OP_bregx
+  .byte 13    // Register SP
+  .byte 4     // Offset 4
+  // End modified debug info.
+  .long 0
+  .long 0
+  .section  .debug_abbrev,"",%progbits
+  .byte 1
+  .byte 17
+  .byte 1
+  .byte 37
+  .byte 14
+  .byte 19
+  .byte 5
+  .byte 3
+  .byte 14
+  .byte 16
+  .byte 23
+  .byte 27
+  .byte 14
+  .byte 17
+  .byte 1
+  .byte 18
+  .byte 6
+  .byte 0
+  .byte 0
+  .byte 2
+  .byte 46
+  .byte 1
+  .byte 3
+  .byte 14
+  .byte 58
+  .byte 11
+  .byte 59
+  .byte 11
+  .byte 39
+  .byte 25
+  .byte 60
+  .byte 25
+  .byte 63
+  .byte 25
+  .byte 0
+  .byte 0
+  .byte 3
+  .byte 5
+  .byte 0
+  .byte 73
+  .byte 19
+  .byte 0
+  .byte 0
+  .byte 4
+  .byte 15
+  .byte 0
+  .byte 73
+  .byte 19
+  .byte 0
+  .byte 0
+  .byte 5
+  .byte 36
+  .byte 0
+  .byte 3
+  .byte 14
+  .byte 62
+  .byte 11
+  .byte 11
+  .byte 11
+  .byte 0
+  .byte 0
+  .byte 6
+  .byte 46
+  .byte 1
+  .byte 17
+  .byte 1
+  .byte 18
+  .byte 6
+  .byte 64
+  .byte 24
+  .ascii  "\227B"
+  .byte 25
+  .byte 3
+  .byte 14
+  .byte 58
+  .byte 11
+  .byte 59
+  .byte 11
+  .byte 39
+  .byte 25
+  .byte 63
+  .byte 25
+  .byte 0
+  .byte 0
+  .byte 7
+  .byte 5
+  .byte 0
+  .byte 2
+  .byte 23
+  .byte 3
+  .byte 14
+  .byte 58
+  .byte 11
+  .byte 59
+  .byte 11
+  .byte 73
+  .byte 19
+  .byte 0
+  .byte 0
+  .byte 8
+  .ascii  "\211\202\001"
+  .byte 0
+  .byte 49
+  .byte 19
+  .byte 17
+  .byte 1
+  .byte 0
+  .byte 0
+  .byte 0
+  .section  .debug_info,"",%progbits
+.Lcu_begin0:
+  .long .Ldebug_info_end0-.Ldebug_info_start0
+.Ldebug_info_start0:
+  .short  4
+  .long .debug_abbrev
+  .byte 4
+  .byte 1
+  .long .Linfo_string0
+  .short  12
+  .long .Linfo_string1
+  .long .Lline_table_start0
+  .long .Linfo_string2
+  .long .Lfunc_begin0
+  .long .Lfunc_end0-.Lfunc_begin0
+  .byte 2
+  .long .Linfo_string3
+  .byte 1
+  .byte 1
+
+
+
+  .byte 3
+  .long 51
+  .byte 0
+  .byte 4
+  .long 56
+  .byte 5
+  .long .Linfo_string4
+  .byte 5
+  .byte 4
+  .byte 6
+  .long .Lfunc_begin0
+  .long .Lfunc_end0-.Lfunc_begin0
+  .byte 1
+  .byte 91
+
+  .long .Linfo_string5
+  .byte 1
+  .byte 2
+
+
+  .byte 7
+  .long .Ldebug_loc0
+  .long .Linfo_string6
+  .byte 1
+  .byte 2
+  .long 56
+  .byte 8
+  .long 38
+  .long .Ltmp2
+  .byte 0
+  .byte 0
+.Ldebug_info_end0:
+  .ident  "clang version 10.0.0 ([e-mail]:llvm/llvm-project.git e73f78acd34360f7450b81167d9dc858ccddc262)"
+  .section  ".note.GNU-stack","",%progbits
+  .addrsig
+  .eabi_attribute 30, 1
+  .section  .debug_line,"",%progbits
+.Lline_table_start0: