teemperor created this revision.
teemperor added reviewers: JDevlieghere, jingham.
Herald added subscribers: lldb-commits, abidh, jfb, christof.
Herald added a project: LLDB.
Currently the data formatter is treating `std::atomic` variables as transparent
wrappers
around their underlying value type. This causes that when printing
`std::atomic<A *>`, the data
formatter will forward all requests for the children of the atomic variable to
the `A *` pointer type
which will then return the respective members of `A`. If `A` in turn has a
member that contains
the original atomic variable, this causes LLDB to infinitely recurse when
printing an object with
such a `std::atomic` pointer member.
We could implement a workaround similar to whatever we do for pointer values
but this patch
just implements the `std::atomic` formatter in the same way as we already
implement other
formatters (e.g. smart pointers or `std::optional`) that just model the
contents of the as a child
"Value". This way LLDB knows when it actually prints a pointer and can just use
its normal
workaround if "Value" is a recursive pointer.
Fixes rdar://59189235
Repository:
rLLDB LLDB
https://reviews.llvm.org/D74310
Files:
lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/atomic/TestLibCxxAtomic.py
lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/atomic/main.cpp
lldb/source/Plugins/Language/CPlusPlus/LibCxxAtomic.cpp
Index: lldb/source/Plugins/Language/CPlusPlus/LibCxxAtomic.cpp
===================================================================
--- lldb/source/Plugins/Language/CPlusPlus/LibCxxAtomic.cpp
+++ lldb/source/Plugins/Language/CPlusPlus/LibCxxAtomic.cpp
@@ -7,6 +7,7 @@
//===----------------------------------------------------------------------===//
#include "LibCxxAtomic.h"
+#include "lldb/DataFormatters/FormattersHelpers.h"
using namespace lldb;
using namespace lldb_private;
@@ -100,8 +101,6 @@
size_t GetIndexOfChildWithName(ConstString name) override;
- lldb::ValueObjectSP GetSyntheticValue() override;
-
private:
ValueObject *m_real_child;
};
@@ -127,26 +126,20 @@
size_t lldb_private::formatters::LibcxxStdAtomicSyntheticFrontEnd::
CalculateNumChildren() {
- return m_real_child ? m_real_child->GetNumChildren() : 0;
+ return m_real_child ? 1 : 0;
}
lldb::ValueObjectSP
lldb_private::formatters::LibcxxStdAtomicSyntheticFrontEnd::GetChildAtIndex(
size_t idx) {
- return m_real_child ? m_real_child->GetChildAtIndex(idx, true) : nullptr;
+ if (idx == 0)
+ return m_real_child->GetSP()->Clone(ConstString("Value"));
+ return nullptr;
}
size_t lldb_private::formatters::LibcxxStdAtomicSyntheticFrontEnd::
GetIndexOfChildWithName(ConstString name) {
- return m_real_child ? m_real_child->GetIndexOfChildWithName(name)
- : UINT32_MAX;
-}
-
-lldb::ValueObjectSP lldb_private::formatters::LibcxxStdAtomicSyntheticFrontEnd::
- GetSyntheticValue() {
- if (m_real_child && m_real_child->CanProvideValue())
- return m_real_child->GetSP();
- return nullptr;
+ return formatters::ExtractIndexFromString(name.GetCString());
}
SyntheticChildrenFrontEnd *
Index: lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/atomic/main.cpp
===================================================================
--- lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/atomic/main.cpp
+++ lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/atomic/main.cpp
@@ -8,6 +8,18 @@
#include <atomic>
+// Define a Parent and Child struct that can point to each other.
+class Parent;
+struct Child {
+ // This should point to the parent which in turn owns this
+ // child instance. This cycle should not cause LLDB to infinite loop
+ // during printing.
+ std::atomic<Parent*> parent{nullptr};
+};
+struct Parent {
+ Child child;
+};
+
struct S {
int x = 1;
int y = 2;
@@ -19,7 +31,11 @@
s.store(S());
std::atomic<int> i;
i.store(5);
-
+
+ Parent p;
+ // Let the child node know what its parent is.
+ p.child.parent = &p;
+
return 0; // Set break point at this line.
}
Index: lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/atomic/TestLibCxxAtomic.py
===================================================================
--- lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/atomic/TestLibCxxAtomic.py
+++ lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/atomic/TestLibCxxAtomic.py
@@ -42,13 +42,19 @@
substrs=['stopped',
'stop reason = breakpoint'])
- s = self.get_variable('s')
- i = self.get_variable('i')
+ s_atomic = self.get_variable('s')
+ i_atomic = self.get_variable('i')
if self.TraceOn():
- print(s)
+ print(s_atomic)
if self.TraceOn():
- print(i)
+ print(i_atomic)
+
+ # Extract the content of the std::atomic wrappers.
+ self.assertEqual(s_atomic.GetNumChildren(), 1)
+ s = s_atomic.GetChildAtIndex(0)
+ self.assertEqual(i_atomic.GetNumChildren(), 1)
+ i = i_atomic.GetChildAtIndex(0)
self.assertTrue(i.GetValueAsUnsigned(0) == 5, "i == 5")
self.assertTrue(s.GetNumChildren() == 2, "s has two children")
@@ -58,3 +64,7 @@
self.assertTrue(
s.GetChildAtIndex(1).GetValueAsUnsigned(0) == 2,
"s.y == 2")
+
+ # Try printing the child that points to its own parent object.
+ # This should just treat the atomic pointer as a normal pointer.
+ self.expect("frame var p.child", substrs=["Value = 0x"])
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