aprantl created this revision.
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Swift async functions receive function arguments inside a heap-allocated data
structure, similar to how ObjC block captures or C++ coroutine arguments are
implement. In DWARF they are described relative to an entry value that produces
a pointer into that heap object. At typical location looks like
`DW_OP_entry_value [ DW_OP_reg14 ] DW_OP_deref DW_OP_plus_uconst 32 DW_OP_deref`
This allows the unwinder (which has special ABI knowledge to restore the
contents of r14) to push the base address onto the stack thus allowing the
deref/offset operations to continue. The result of the entry value is a scalar,
because DW_OP_reg14 is a register location — as it should be since we want to
restore the pointer value contained in r14 at the beginning of the function and
not the historical memory contents it was pointing to. The entry value should
restore the address, which is still valid, not the contents at function entry.
To make this work, we need to allow LLDB to dereference Scalar stack results
like load addresses, which is what this patch does. Unfortunately it is
difficult to test this in isolation, since the DWARFExpression unit test
doesn't have a process. Are there any situations where we shouldn't allow
Scalars to be dereferences? Could they ever hold a File- or Hostaddress? I
don't think so.
https://reviews.llvm.org/D96549
Files:
lldb/source/Expression/DWARFExpression.cpp
Index: lldb/source/Expression/DWARFExpression.cpp
===================================================================
--- lldb/source/Expression/DWARFExpression.cpp
+++ lldb/source/Expression/DWARFExpression.cpp
@@ -1067,6 +1067,7 @@
stack.back().SetValueType(Value::ValueType::LoadAddress);
// Fall through to load address code below...
} LLVM_FALLTHROUGH;
+ case Value::ValueType::Scalar:
case Value::ValueType::LoadAddress:
if (exe_ctx) {
if (process) {
@@ -1099,7 +1100,6 @@
}
break;
- case Value::ValueType::Scalar:
case Value::ValueType::Invalid:
if (error_ptr)
error_ptr->SetErrorString("Invalid value type for DW_OP_deref.\n");
@@ -1170,6 +1170,7 @@
stack.back().GetScalar() = ptr;
stack.back().ClearContext();
} break;
+ case Value::ValueType::Scalar:
case Value::ValueType::LoadAddress:
if (exe_ctx) {
if (process) {
@@ -1221,7 +1222,6 @@
}
break;
- case Value::ValueType::Scalar:
case Value::ValueType::FileAddress:
case Value::ValueType::Invalid:
if (error_ptr)
Index: lldb/source/Expression/DWARFExpression.cpp
===================================================================
--- lldb/source/Expression/DWARFExpression.cpp
+++ lldb/source/Expression/DWARFExpression.cpp
@@ -1067,6 +1067,7 @@
stack.back().SetValueType(Value::ValueType::LoadAddress);
// Fall through to load address code below...
} LLVM_FALLTHROUGH;
+ case Value::ValueType::Scalar:
case Value::ValueType::LoadAddress:
if (exe_ctx) {
if (process) {
@@ -1099,7 +1100,6 @@
}
break;
- case Value::ValueType::Scalar:
case Value::ValueType::Invalid:
if (error_ptr)
error_ptr->SetErrorString("Invalid value type for DW_OP_deref.\n");
@@ -1170,6 +1170,7 @@
stack.back().GetScalar() = ptr;
stack.back().ClearContext();
} break;
+ case Value::ValueType::Scalar:
case Value::ValueType::LoadAddress:
if (exe_ctx) {
if (process) {
@@ -1221,7 +1222,6 @@
}
break;
- case Value::ValueType::Scalar:
case Value::ValueType::FileAddress:
case Value::ValueType::Invalid:
if (error_ptr)
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