[llvm-objdump] Add entry_value locations to variable display

[ostannard]

Summary

This adds the DW_OP_entry_value and DW_OP_stack_value opcodes to the DWARF expression printer, needed to display variable locations which refer to the value of an expression at entry to the function.

[aprantl]

llvm/test/tools/llvm-objdump/ARM/debug-vars-entry-value.s

2

It would be a lot more efficient to test this in unittests/DebugInfo/dwarf, but just dumping the expression bytes themselves. Otherwise the canonical place to test dwarf dumping facilities is usually llvm-dwarfdump.

I'm kind of worried that this test will need to be updated every time someone tunes the output formatting of objdump

[jhenderson]

llvm/test/tools/llvm-objdump/ARM/debug-vars-entry-value.s

2

+1 to this. The prettyPrint function looks ripe for gtest unit testing. I wouldn't necessarily worry about covering every code path in the first instance, but you could work towards it that way.

[ostannard]

Convert tests to unit tests.

[aprantl]

llvm/test/tools/llvm-objdump/ARM/debug-vars-entry-value.s

2

I think this test should be deleted now, it doesn't add anything over the unit test, right?

llvm/unittests/DebugInfo/DWARF/DWARFExpressionCompactPrinterTest.cpp

105

Nice.

[ostannard]

• Delete old test

[jhenderson]

LGTM too.

llvm/include/llvm/DebugInfo/DWARF/DWARFExpression.h

class Operation &operator++() {
           !Op.extract(Expr->Data, Expr->AddressSize, Offset);
       return Op;
     }
 
     class Operation &operator*() {
       return Op;
     }
 
+    iterator skipBytes(uint64_t Add) {
+      return iterator(Expr, Op.EndOffset + Add);
+    }
+
     // Comparison operators are provided out of line.
     friend bool operator==(const iterator &, const iterator &);
   };
 
   DWARFExpression(DataExtractor Data, uint8_t AddressSize)
       : Data(Data), AddressSize(AddressSize) {
     assert(AddressSize == 8 || AddressSize == 4 || AddressSize == 2);
   }

llvm/lib/DebugInfo/DWARF/DWARFExpression.cpp

case dwarf::DW_OP_bregx: {
         return false;
       }
       raw_svector_ostream S(Stack.emplace_back().String);
       S << MRI->getName(*LLVMRegNum);
       if (Offset)
         S << format("%+" PRId64, Offset);
       break;
     }
+    case dwarf::DW_OP_entry_value:
+    case dwarf::DW_OP_GNU_entry_value: {
+      // DW_OP_entry_value contains a sub-expression which must be rendered
+      // separately.
+      uint64_t SubExprLength = Op.getRawOperand(0);
+      DWARFExpression::iterator SubExprEnd = I.skipBytes(SubExprLength);
+      ++I;
+      raw_svector_ostream S(Stack.emplace_back().String);
+      S << "entry(";
+      printCompactDWARFExpr(S, I, SubExprEnd, MRI);
+      S << ")";
+      I = SubExprEnd;
+      continue;
+    }
+    case dwarf::DW_OP_stack_value: {
+      // The top stack entry should be treated as the actual value of tne
+      // variable, rather than the address of the variable in memory.
+      assert(!Stack.empty());
+      Stack.back().Kind = PrintedExpr::Value;
+      break;
+    }
     default:
       if (Opcode >= dwarf::DW_OP_reg0 && Opcode <= dwarf::DW_OP_reg31) {
         // DW_OP_reg<N>: A register, with the register num implied by the
         // opcode. Printed as the plain register name.
         uint64_t DwarfRegNum = Opcode - dwarf::DW_OP_reg0;
         Optional<unsigned> LLVMRegNum = MRI->getLLVMRegNum(DwarfRegNum, false);
         if (!LLVMRegNum) {
           OS << "<unknown register " << DwarfRegNum << ">";

llvm/test/tools/llvm-objdump/ARM/debug-vars-entry-value.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 the DW_OP_entry_value opcode,
+## which also requires the DW_OP_stack_value opcode.
+
+## Generated with this compile command and source code:
+## arm-none-eabi-gcc -march=armv7-a -c debug.c -O1 -g -S -o - -gno-as-locview-support
+
+## int foo(int a, int b) {
+##   return a + b;
+## }
+
+# CHECK: 00000000 foo:
+# CHECK-NEXT:                                                                   ┠─ a = R0
+# CHECK-NEXT:                                                                   ┃ ┌─ a = entry(R0)
+# CHECK-NEXT:                                                                   ┃ │ ┠─ b = R1
+# CHECK-NEXT:        0:       add     r0, r0, r1                                ┻ ╈ ┃
+# CHECK-NEXT:        4:       bx      lr                                          ┻ ┻
+
+  .arch armv7-a
+  .eabi_attribute 20, 1
+  .eabi_attribute 21, 1
+  .eabi_attribute 23, 3
+  .eabi_attribute 24, 1
+  .eabi_attribute 25, 1
+  .eabi_attribute 26, 1
+  .eabi_attribute 30, 1
+  .eabi_attribute 34, 1
+  .eabi_attribute 18, 4
+  .file "debug.c"
+  .text
+.Ltext0:
+  .cfi_sections .debug_frame
+  .align  2
+  .global foo
+  .syntax unified
+  .arm
+  .fpu softvfp
+  .type foo, %function
+foo:
+.LFB0:
+  .file 1 "debug.c"
+  .loc 1 1 23
+  .cfi_startproc
+  @ args = 0, pretend = 0, frame = 0
+  @ frame_needed = 0, uses_anonymous_args = 0
+  @ link register save eliminated.
+.LVL0:
+  .loc 1 2 3
+  .loc 1 3 1 is_stmt 0
+  add r0, r0, r1
+.LVL1:
+  bx  lr
+  .cfi_endproc
+.LFE0:
+  .size foo, .-foo
+.Letext0:
+  .section  .debug_info,"",%progbits
+.Ldebug_info0:
+  .4byte  0x5e
+  .2byte  0x4
+  .4byte  .Ldebug_abbrev0
+  .byte 0x4
+  .uleb128 0x1
+  .4byte  .LASF0
+  .byte 0xc
+  .4byte  .LASF1
+  .4byte  .LASF2
+  .4byte  .Ltext0
+  .4byte  .Letext0-.Ltext0
+  .4byte  .Ldebug_line0
+  .uleb128 0x2
+  .ascii  "foo\000"
+  .byte 0x1
+  .byte 0x1
+  .byte 0x5
+  .4byte  0x5a
+  .4byte  .LFB0
+  .4byte  .LFE0-.LFB0
+  .uleb128 0x1
+  .byte 0x9c
+  .4byte  0x5a
+  .uleb128 0x3
+  .ascii  "a\000"
+  .byte 0x1
+  .byte 0x1
+  .byte 0xd
+  .4byte  0x5a
+  .4byte  .LLST0
+  .uleb128 0x4
+  .ascii  "b\000"
+  .byte 0x1
+  .byte 0x1
+  .byte 0x14
+  .4byte  0x5a
+  .uleb128 0x1
+  .byte 0x51
+  .byte 0
+  .uleb128 0x5
+  .byte 0x4
+  .byte 0x5
+  .ascii  "int\000"
+  .byte 0
+  .section  .debug_abbrev,"",%progbits
+.Ldebug_abbrev0:
+  .uleb128 0x1
+  .uleb128 0x11
+  .byte 0x1
+  .uleb128 0x25
+  .uleb128 0xe
+  .uleb128 0x13
+  .uleb128 0xb
+  .uleb128 0x3
+  .uleb128 0xe
+  .uleb128 0x1b
+  .uleb128 0xe
+  .uleb128 0x11
+  .uleb128 0x1
+  .uleb128 0x12
+  .uleb128 0x6
+  .uleb128 0x10
+  .uleb128 0x17
+  .byte 0
+  .byte 0
+  .uleb128 0x2
+  .uleb128 0x2e
+  .byte 0x1
+  .uleb128 0x3f
+  .uleb128 0x19
+  .uleb128 0x3
+  .uleb128 0x8
+  .uleb128 0x3a
+  .uleb128 0xb
+  .uleb128 0x3b
+  .uleb128 0xb
+  .uleb128 0x39
+  .uleb128 0xb
+  .uleb128 0x27
+  .uleb128 0x19
+  .uleb128 0x49
+  .uleb128 0x13
+  .uleb128 0x11
+  .uleb128 0x1
+  .uleb128 0x12
+  .uleb128 0x6
+  .uleb128 0x40
+  .uleb128 0x18
+  .uleb128 0x2117
+  .uleb128 0x19
+  .uleb128 0x1
+  .uleb128 0x13
+  .byte 0
+  .byte 0
+  .uleb128 0x3
+  .uleb128 0x5
+  .byte 0
+  .uleb128 0x3
+  .uleb128 0x8
+  .uleb128 0x3a
+  .uleb128 0xb
+  .uleb128 0x3b
+  .uleb128 0xb
+  .uleb128 0x39
+  .uleb128 0xb
+  .uleb128 0x49
+  .uleb128 0x13
+  .uleb128 0x2
+  .uleb128 0x17
+  .byte 0
+  .byte 0
+  .uleb128 0x4
+  .uleb128 0x5
+  .byte 0
+  .uleb128 0x3
+  .uleb128 0x8
+  .uleb128 0x3a
+  .uleb128 0xb
+  .uleb128 0x3b
+  .uleb128 0xb
+  .uleb128 0x39
+  .uleb128 0xb
+  .uleb128 0x49
+  .uleb128 0x13
+  .uleb128 0x2
+  .uleb128 0x18
+  .byte 0
+  .byte 0
+  .uleb128 0x5
+  .uleb128 0x24
+  .byte 0
+  .uleb128 0xb
+  .uleb128 0xb
+  .uleb128 0x3e
+  .uleb128 0xb
+  .uleb128 0x3
+  .uleb128 0x8
+  .byte 0
+  .byte 0
+  .byte 0
+  .section  .debug_loc,"",%progbits
+.Ldebug_loc0:
+.LLST0:
+  .4byte  .LVL0-.Ltext0
+  .4byte  .LVL1-.Ltext0
+  .2byte  0x1
+  .byte 0x50
+  .4byte  .LVL1-.Ltext0
+  .4byte  .LFE0-.Ltext0
+  .2byte  0x4
+  .byte 0xf3
+  .uleb128 0x1
+  .byte 0x50
+  .byte 0x9f
+  .4byte  0
+  .4byte  0
+  .section  .debug_aranges,"",%progbits
+  .4byte  0x1c
+  .2byte  0x2
+  .4byte  .Ldebug_info0
+  .byte 0x4
+  .byte 0
+  .2byte  0
+  .2byte  0
+  .4byte  .Ltext0
+  .4byte  .Letext0-.Ltext0
+  .4byte  0
+  .4byte  0
+  .section  .debug_line,"",%progbits
+.Ldebug_line0:
+  .section  .debug_str,"MS",%progbits,1
+.LASF0:
+  .ascii  "GNU C17 10.0.0 20190731 (experimental) -mfloat-abi="
+  .ascii  "soft -marm -march=armv7-a -g -gno-as-locview-suppor"
+  .ascii  "t -O1\000"
+.LASF2:
+  .ascii  "/work/scratch\000"
+.LASF1:
+  .ascii  "debug.c\000"
+  .ident  "GCC: (fsf-trunk.1961) 10.0.0 20190731 (experimental)"

llvm/unittests/DebugInfo/DWARF/DWARFExpressionCompactPrinterTest.cpp

 
 TEST_F(DWARFExpressionCompactPrinterTest, Test_OP_breg0_negative) {
   TestExprPrinter({DW_OP_breg0, 0x70}, "[R0-16]");
 }
 
 TEST_F(DWARFExpressionCompactPrinterTest, Test_OP_bregx) {
   TestExprPrinter({DW_OP_bregx, 0x0d, 0x28}, "[SP+40]");
 }
+
+TEST_F(DWARFExpressionCompactPrinterTest, Test_OP_stack_value) {
+  TestExprPrinter({DW_OP_breg13, 0x04, DW_OP_stack_value}, "SP+4");
+}
+
+TEST_F(DWARFExpressionCompactPrinterTest, Test_OP_entry_value) {
+  TestExprPrinter({DW_OP_entry_value, 0x01, DW_OP_reg0, DW_OP_stack_value},
+                  "entry(R0)");
+}
+
+TEST_F(DWARFExpressionCompactPrinterTest, Test_OP_entry_value_mem) {
+  TestExprPrinter(
+      {DW_OP_entry_value, 0x02, DW_OP_breg13, 0x10, DW_OP_stack_value},
+      "entry([SP+16])");
+}