[llvm] r344960 - [DWARF] Use a function-local offset for AT_call_return_pc
Vedant Kumar via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 22 14:44:21 PDT 2018
Author: vedantk
Date: Mon Oct 22 14:44:21 2018
New Revision: 344960
URL: http://llvm.org/viewvc/llvm-project?rev=344960&view=rev
Log:
[DWARF] Use a function-local offset for AT_call_return_pc
Logs provided by @stella.stamenova indicate that on Linux, lldb adds a
spurious slide offset to the return PC it loads from AT_call_return_pc
attributes (see the list thread: "[PATCH] D50478: Add support for
artificial tail call frames").
This patch side-steps the issue by getting rid of the load address
calculation in lldb's CallEdge::GetReturnPCAddress.
The idea is to have the DWARF writer emit function-local offsets to the
instruction after a call. I.e. return-pc = label-after-call-insn -
function-entry. LLDB can simply add this offset to the base address of a
function to get the return PC.
Differential Revision: https://reviews.llvm.org/D53469
Modified:
llvm/trunk/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
llvm/trunk/lib/CodeGen/AsmPrinter/DebugHandlerBase.h
llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp?rev=344960&r1=344959&r2=344960&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp (original)
+++ llvm/trunk/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp Mon Oct 22 14:44:21 2018
@@ -125,6 +125,21 @@ MCSymbol *DebugHandlerBase::getLabelAfte
return LabelsAfterInsn.lookup(MI);
}
+// Return the function-local offset of an instruction.
+const MCExpr *
+DebugHandlerBase::getFunctionLocalOffsetAfterInsn(const MachineInstr *MI) {
+ MCContext &MC = Asm->OutContext;
+
+ MCSymbol *Start = Asm->getFunctionBegin();
+ const auto *StartRef = MCSymbolRefExpr::create(Start, MC);
+
+ MCSymbol *AfterInsn = getLabelAfterInsn(MI);
+ assert(AfterInsn && "Expected label after instruction");
+ const auto *AfterRef = MCSymbolRefExpr::create(AfterInsn, MC);
+
+ return MCBinaryExpr::createSub(AfterRef, StartRef, MC);
+}
+
/// If this type is derived from a base type then return base type size.
uint64_t DebugHandlerBase::getBaseTypeSize(const DITypeRef TyRef) {
DIType *Ty = TyRef.resolve();
Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DebugHandlerBase.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DebugHandlerBase.h?rev=344960&r1=344959&r2=344960&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/AsmPrinter/DebugHandlerBase.h (original)
+++ llvm/trunk/lib/CodeGen/AsmPrinter/DebugHandlerBase.h Mon Oct 22 14:44:21 2018
@@ -125,6 +125,10 @@ public:
/// Return Label immediately following the instruction.
MCSymbol *getLabelAfterInsn(const MachineInstr *MI);
+ /// Return the function-local offset of an instruction. A label for the
+ /// instruction \p MI should exist (\ref getLabelAfterInsn).
+ const MCExpr *getFunctionLocalOffsetAfterInsn(const MachineInstr *MI);
+
/// If this type is derived from a base type then return base type size.
static uint64_t getBaseTypeSize(const DITypeRef TyRef);
};
Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp?rev=344960&r1=344959&r2=344960&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp (original)
+++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp Mon Oct 22 14:44:21 2018
@@ -821,7 +821,7 @@ void DwarfCompileUnit::constructAbstract
DIE &DwarfCompileUnit::constructCallSiteEntryDIE(DIE &ScopeDIE,
const DISubprogram &CalleeSP,
bool IsTail,
- const MCSymbol *ReturnPC) {
+ const MCExpr *PCOffset) {
// Insert a call site entry DIE within ScopeDIE.
DIE &CallSiteDIE =
createAndAddDIE(dwarf::DW_TAG_call_site, ScopeDIE, nullptr);
@@ -838,8 +838,8 @@ DIE &DwarfCompileUnit::constructCallSite
} else {
// Attach the return PC to allow the debugger to disambiguate call paths
// from one function to another.
- assert(ReturnPC && "Missing return PC information for a call");
- addLabelAddress(CallSiteDIE, dwarf::DW_AT_call_return_pc, ReturnPC);
+ assert(PCOffset && "Missing return PC information for a call");
+ addAddressExpr(CallSiteDIE, dwarf::DW_AT_call_return_pc, PCOffset);
}
return CallSiteDIE;
}
@@ -1103,6 +1103,12 @@ void DwarfCompileUnit::addExpr(DIELoc &D
Die.addValue(DIEValueAllocator, (dwarf::Attribute)0, Form, DIEExpr(Expr));
}
+void DwarfCompileUnit::addAddressExpr(DIE &Die, dwarf::Attribute Attribute,
+ const MCExpr *Expr) {
+ Die.addValue(DIEValueAllocator, Attribute, dwarf::DW_FORM_addr,
+ DIEExpr(Expr));
+}
+
void DwarfCompileUnit::applySubprogramAttributesToDefinition(
const DISubprogram *SP, DIE &SPDie) {
auto *SPDecl = SP->getDeclaration();
Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h?rev=344960&r1=344959&r2=344960&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h (original)
+++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h Mon Oct 22 14:44:21 2018
@@ -210,10 +210,10 @@ public:
/// Construct a call site entry DIE describing a call within \p Scope to a
/// callee described by \p CalleeSP. \p IsTail specifies whether the call is
- /// a tail call. \p ReturnPC must be non-null for non-tail calls and point
- /// to the PC value after the call returns.
+ /// a tail call. \p PCOffset must be non-zero for non-tail calls or be the
+ /// function-local offset to PC value after the call instruction.
DIE &constructCallSiteEntryDIE(DIE &ScopeDIE, const DISubprogram &CalleeSP,
- bool IsTail, const MCSymbol *ReturnPC);
+ bool IsTail, const MCExpr *PCOffset);
/// Construct import_module DIE.
DIE *constructImportedEntityDIE(const DIImportedEntity *Module);
@@ -292,6 +292,9 @@ public:
/// Add a Dwarf expression attribute data and value.
void addExpr(DIELoc &Die, dwarf::Form Form, const MCExpr *Expr);
+ /// Add an attribute containing an address expression to \p Die.
+ void addAddressExpr(DIE &Die, dwarf::Attribute Attribute, const MCExpr *Expr);
+
void applySubprogramAttributesToDefinition(const DISubprogram *SP,
DIE &SPDie);
Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp?rev=344960&r1=344959&r2=344960&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp (original)
+++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp Mon Oct 22 14:44:21 2018
@@ -548,14 +548,15 @@ void DwarfDebug::constructCallSiteEntryD
// For tail calls, no return PC information is needed. For regular calls,
// the return PC is needed to disambiguate paths in the call graph which
// could lead to some target function.
- const MCSymbol *ReturnPC = IsTail ? nullptr : getLabelAfterInsn(&MI);
+ const MCExpr *PCOffset =
+ IsTail ? nullptr : getFunctionLocalOffsetAfterInsn(&MI);
- assert((IsTail || ReturnPC) && "Call without return PC information");
+ assert((IsTail || PCOffset) && "Call without return PC information");
LLVM_DEBUG(dbgs() << "CallSiteEntry: " << MF.getName() << " -> "
<< CalleeDecl->getName() << (IsTail ? " [tail]" : "")
<< "\n");
CU.constructCallSiteEntryDIE(ScopeDIE, *CalleeDecl->getSubprogram(),
- IsTail, ReturnPC);
+ IsTail, PCOffset);
}
}
}
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