DWARFExpression: Resolve file addresses in the linked module

This is a follow-up to https://reviews.llvm.org/D46362.

When evaluating a complex expression in DWARFExpression::Evaluate,
file addresses must be resolved to load addresses before we can
perform operations such as DW_OP_deref on them.

For this the address goes through three steps

1. Read the file address as stored in the DWARF
2. Link/relocate the file address (when reading from a .dSYM, this is a no-op)
3. Convert the file address to a load address.

D46362 implemented step (3) by resolving the file address using the
Module that the original DWARF came from. In the case of a dSYM that
is correct, but when reading from .o files, we need to look up
relocated/linked addresses, so the right place to look them up is the
current frame's module. This patch fixes that by setting the
expression's Module to point to the linked debugmap object.

A word a bout the unorthodox testcase: The motivating testcase for
this fix is in Swift, but I managed to hand-modify LLVM-IR for a
trivial C program to exhibit the same problem, so we can fix this in
llvm.org.

rdar://problem/44689915

Differential Revision: https://reviews.llvm.org/D52678

llvm-svn: 343612

lldb/include/lldb/Expression/DWARFExpression.h

@@ -152,6 +152,8 @@ class DWARFExpression {
   lldb::addr_t GetLocation_DW_OP_addr(uint32_t op_addr_idx, bool &error) const;
 
   bool Update_DW_OP_addr(lldb::addr_t file_addr);
+
+  void SetModule(const lldb::ModuleSP &module) { m_module_wp = module; }
 
   bool ContainsThreadLocalStorage() const;
 

lldb/packages/Python/lldbsuite/test/functionalities/target_var/Makefile

@@ -0,0 +1,10 @@
+LEVEL = ../../make
+
+include $(LEVEL)/Makefile.rules
+
+a.out: globals.ll
+	$(CC) $(CFLAGS) -g -c $^ -o globals.o
+	$(LD) $(LDFLAGS) -g globals.o -o $@
+
+clean::
+	rm -rf globals.o a.out *.dSYM

lldb/packages/Python/lldbsuite/test/functionalities/target_var/TestTargetVar.py

@@ -0,0 +1,22 @@
+"""
+Test that target var can resolve complex DWARF expressions.
+"""
+
+import lldb
+import sys
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class targetCommandTestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @skipUnlessDarwin
+    @skipIfDarwinEmbedded           # needs x86_64
+    @skipIf(debug_info="gmodules")  # not relevant
+    def testTargetVarExpr(self):
+        self.build()
+        lldbutil.run_to_name_breakpoint(self, 'main')
+        self.expect("target variable i", substrs=['i', '42'])

lldb/packages/Python/lldbsuite/test/functionalities/target_var/globals.c

@@ -0,0 +1,6 @@
+int i = 42;
+int *p = &i;
+
+int main() {
+  return *p;
+}

lldb/packages/Python/lldbsuite/test/functionalities/target_var/globals.ll

@@ -0,0 +1,42 @@
+source_filename = "globals.c"
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.14.0"
+
+@i = global i32 42, align 4
+@p = global i32* @i, align 8, !dbg !0, !dbg !6
+
+; Function Attrs: noinline nounwind optnone ssp uwtable
+define i32 @main() #0 !dbg !15 {
+entry:
+  %retval = alloca i32, align 4
+  store i32 0, i32* %retval, align 4
+  %0 = load i32*, i32** @p, align 8, !dbg !18
+  %1 = load i32, i32* %0, align 4, !dbg !18
+  ret i32 %1, !dbg !18
+}
+
+attributes #0 = { noinline nounwind optnone ssp uwtable }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!10, !11, !12, !13}
+!llvm.ident = !{!14}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression(DW_OP_deref))
+!1 = distinct !DIGlobalVariable(name: "i", scope: !2, file: !3, line: 1, type: !9, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, emissionKind: FullDebug, globals: !5, nameTableKind: None)
+!3 = !DIFile(filename: "globals.c", directory: "/")
+!4 = !{}
+!5 = !{!0, !6}
+!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = distinct !DIGlobalVariable(name: "p", scope: !2, file: !3, line: 2, type: !8, isLocal: false, isDefinition: true)
+!8 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64)
+!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!10 = !{i32 2, !"Dwarf Version", i32 4}
+!11 = !{i32 2, !"Debug Info Version", i32 3}
+!12 = !{i32 1, !"wchar_size", i32 4}
+!13 = !{i32 7, !"PIC Level", i32 2}
+!14 = !{!"clang version 8.0.0 (trunk 340838) (llvm/trunk 340843)"}
+!15 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 4, type: !16, isLocal: false, isDefinition: true, scopeLine: 4, isOptimized: false, unit: !2, retainedNodes: !4)
+!16 = !DISubroutineType(types: !17)
+!17 = !{!9}
+!18 = !DILocation(line: 5, scope: !15)

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

@@ -3437,6 +3437,11 @@ VariableSP SymbolFileDWARF::ParseVariableDIE(const SymbolContext &sc,
             is_static_lifetime = true;
         }
         SymbolFileDWARFDebugMap *debug_map_symfile = GetDebugMapSymfile();
+        if (debug_map_symfile)
+          // Set the module of the expression to the linked module
+          // instead of the oject file so the relocated address can be
+          // found there.
+          location.SetModule(debug_map_symfile->GetObjectFile()->GetModule());
 
         if (is_static_lifetime) {
           if (is_external)