[Lldb-commits] [PATCH] D61018: RegisterContextLLDB: Push CFA value on DWARF stack when evaluating register expressions

[Pavel Labath via Phabricator via lldb-commits]

labath created this revision.
labath added reviewers: jasonmolenda, clayborg.
Herald added a subscriber: aprantl.

This behavior is specified in the Section 6.4.2.3 (Register Rule
instructions) of the DWARF4 spec. We were not doing that, which meant
that any register rule which was relying on the cfa value being there
was not evaluated correctly (it was aborted due to "out of bounds"
access).

I'm not sure how come this wasn't noticed before, but I guess this has
something to do with the fact that dwarf unwind expressions are not used
very often, and when they are, the situation is so complicated that the
CFA is of no use. I noticed this when I started emitting dwarf
expressions for the unwind information present in breakpad symbol files.


https://reviews.llvm.org/D61018

Files:
  lit/Unwind/Inputs/eh-frame-dwarf-unwind.s
  lit/Unwind/eh-frame-dwarf-unwind.test
  source/Plugins/Process/Utility/RegisterContextLLDB.cpp


Index: source/Plugins/Process/Utility/RegisterContextLLDB.cpp
===================================================================
--- source/Plugins/Process/Utility/RegisterContextLLDB.cpp
+++ source/Plugins/Process/Utility/RegisterContextLLDB.cpp
@@ -1507,9 +1507,11 @@
     DWARFExpression dwarfexpr(opcode_ctx, dwarfdata, nullptr, 0,
                               unwindplan_regloc.GetDWARFExpressionLength());
     dwarfexpr.SetRegisterKind(unwindplan_registerkind);
+    Value cfa_val = Scalar(m_cfa);
+    cfa_val.SetValueType(Value::eValueTypeLoadAddress);
     Value result;
     Status error;
-    if (dwarfexpr.Evaluate(&exe_ctx, this, 0, nullptr, nullptr, result,
+    if (dwarfexpr.Evaluate(&exe_ctx, this, 0, &cfa_val, nullptr, result,
                            &error)) {
       addr_t val;
       val = result.GetScalar().ULongLong();
Index: lit/Unwind/eh-frame-dwarf-unwind.test
===================================================================
--- /dev/null
+++ lit/Unwind/eh-frame-dwarf-unwind.test
@@ -0,0 +1,22 @@
+# Test handing of dwarf expressions specifying the location of registers, if
+# those expressions refer to the frame's CFA value.
+
+# REQUIRES: target-x86_64, system-linux, native
+
+# RUN: %clang %p/Inputs/eh-frame-dwarf-unwind.s -o %t
+# RUN: %lldb %t -s %s -o exit | FileCheck %s
+
+breakpoint set -n bar
+# CHECK: Breakpoint 1: where = {{.*}}`bar
+
+process launch
+# CHECK: stop reason = breakpoint 1.1
+
+thread backtrace
+# CHECK: frame #0: {{.*}}`bar
+# CHECK: frame #1: {{.*}}`foo + 5
+# CHECK: frame #2: {{.*}}`main + 19
+
+target modules show-unwind -n foo
+# CHECK: eh_frame UnwindPlan:
+# CHECK: row[0]: 0: CFA=rsp +8 => rip=DW_OP_lit8 , DW_OP_minus , DW_OP_deref , DW_OP_const1u 0x47, DW_OP_minus
Index: lit/Unwind/Inputs/eh-frame-dwarf-unwind.s
===================================================================
--- /dev/null
+++ lit/Unwind/Inputs/eh-frame-dwarf-unwind.s
@@ -0,0 +1,49 @@
+        .text
+        .globl  bar
+        .type   bar, @function
+bar:
+.LFB0:
+        .cfi_startproc
+        leal    (%edi, %edi), %eax
+        ret
+        .cfi_endproc
+.LFE0:
+        .size   bar, .-bar
+        .globl  foo
+        .type   foo, @function
+foo:
+.LFB1:
+        .cfi_startproc
+        .cfi_escape 0x16, 0x10, 0x06, 0x38, 0x1c, 0x06, 0x08, 0x47, 0x1c
+        call    bar
+        addl    $1, %eax
+        popq    %rdi
+        subq    $0x47, %rdi
+        jmp     *%rdi # Return
+        .cfi_endproc
+.LFE1:
+        .size   foo, .-foo
+        .globl  main
+        .type   main, @function
+main:
+.LFB2:
+        .cfi_startproc
+        pushq   %rbp
+        .cfi_def_cfa_offset 16
+        .cfi_offset 6, -16
+        movq    %rsp, %rbp
+        .cfi_def_cfa_register 6
+        movl    $47, %edi
+
+        # Non-standard calling convention. The real return address must be
+        # decremented by 0x47.
+        leaq    0x47+1f(%rip), %rax
+        pushq   %rax
+        jmp     foo # call
+1:
+        popq    %rbp
+        .cfi_def_cfa 7, 8
+        ret
+        .cfi_endproc
+.LFE2:
+        .size   main, .-main


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