[lldb] Fix StdUnorderedMapSynthProvider for GCC (llvm#164251)

DrSergei · Debadri Basak · commit ea30df1f73a3 · 2025-11-03T11:34:28.000Z
This patch adds small workaround for [issue](llvm#152504). It looks like code compiled with gcc has lack of some important debug information (e.g. DW_TAG_template_type_parameter for allocator). Example code: ```cpp #include <unordered_map> int main() { std::unordered_map<int, int> map = { {1, 2} }; return 0; } ``` Output from `llvm-dwarfdump` for code compiled by GCC or Clang. I used system GCC (13.3.0) and Clang (18.1.3) on Ubuntu 24.04 (WSL). GCC: ``` 0x00001fcd: DW_TAG_class_type DW_AT_name ("allocator<std::pair<int const, int> >") DW_AT_byte_size (0x01) DW_AT_decl_file ("/usr/include/c++/13/bits/allocator.h") DW_AT_decl_line (130) DW_AT_decl_column (11) DW_AT_sibling (0x0000207c) 0x00001fda: DW_TAG_inheritance DW_AT_type (0x00001d0a "std::__new_allocator<std::pair<int const, int> >") DW_AT_data_member_location (0) DW_AT_accessibility (DW_ACCESS_public) 0x00001fe0: DW_TAG_subprogram DW_AT_external (true) DW_AT_name ("allocator") DW_AT_decl_file ("/usr/include/c++/13/bits/allocator.h") DW_AT_decl_line (163) DW_AT_decl_column (7) DW_AT_linkage_name ("_ZNSaISt4pairIKiiEEC4Ev") DW_AT_accessibility (DW_ACCESS_public) DW_AT_declaration (true) DW_AT_object_pointer (0x00001ff4) DW_AT_sibling (0x00001ffa) 0x00001ff4: DW_TAG_formal_parameter DW_AT_type (0x00004eb9 "std::allocator<std::pair<int const, int> > *") DW_AT_artificial (true) 0x00001ff9: NULL 0x00001ffa: DW_TAG_subprogram DW_AT_external (true) DW_AT_name ("allocator") DW_AT_decl_file ("/usr/include/c++/13/bits/allocator.h") DW_AT_decl_line (167) DW_AT_decl_column (7) DW_AT_linkage_name ("_ZNSaISt4pairIKiiEEC4ERKS2_") DW_AT_accessibility (DW_ACCESS_public) DW_AT_declaration (true) DW_AT_object_pointer (0x0000200e) DW_AT_sibling (0x00002019) 0x0000200e: DW_TAG_formal_parameter DW_AT_type (0x00004eb9 "std::allocator<std::pair<int const, int> > *") DW_AT_artificial (true) 0x00002013: DW_TAG_formal_parameter DW_AT_type (0x00004ec3 "const std::allocator<std::pair<int const, int> > &") 0x00002018: NULL 0x00002019: DW_TAG_subprogram DW_AT_external (true) DW_AT_name ("operator=") DW_AT_decl_file ("/usr/include/c++/13/bits/allocator.h") DW_AT_decl_line (172) DW_AT_decl_column (18) DW_AT_linkage_name ("_ZNSaISt4pairIKiiEEaSERKS2_") DW_AT_type (0x00004ec8 "std::allocator<std::pair<int const, int> > &") DW_AT_accessibility (DW_ACCESS_public) DW_AT_declaration (true) DW_AT_defaulted (DW_DEFAULTED_in_class) DW_AT_object_pointer (0x00002031) DW_AT_sibling (0x0000203c) 0x00002031: DW_TAG_formal_parameter DW_AT_type (0x00004eb9 "std::allocator<std::pair<int const, int> > *") DW_AT_artificial (true) 0x00002036: DW_TAG_formal_parameter DW_AT_type (0x00004ec3 "const std::allocator<std::pair<int const, int> > &") 0x0000203b: NULL 0x0000203c: DW_TAG_subprogram DW_AT_external (true) DW_AT_name ("~allocator") DW_AT_decl_file ("/usr/include/c++/13/bits/allocator.h") DW_AT_decl_line (184) DW_AT_decl_column (7) DW_AT_linkage_name ("_ZNSaISt4pairIKiiEED4Ev") DW_AT_accessibility (DW_ACCESS_public) DW_AT_declaration (true) DW_AT_object_pointer (0x00002050) DW_AT_sibling (0x0000205b) 0x00002050: DW_TAG_formal_parameter DW_AT_type (0x00004eb9 "std::allocator<std::pair<int const, int> > *") DW_AT_artificial (true) 0x00002055: DW_TAG_formal_parameter DW_AT_type (0x00004cab "int") DW_AT_artificial (true) 0x0000205a: NULL ``` Clang: ``` 0x00001a6e: DW_TAG_class_type DW_AT_calling_convention (DW_CC_pass_by_reference) DW_AT_name ("allocator<std::pair<const int, int> >") DW_AT_byte_size (0x01) DW_AT_decl_file ("/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/bits/allocator.h") DW_AT_decl_line (130) 0x00001a74: DW_TAG_template_type_parameter DW_AT_type (0x00000dec "std::pair<const int, int>") DW_AT_name ("_Tp") 0x00001a7a: DW_TAG_inheritance DW_AT_type (0x00001ad5 "std::__allocator_base<std::pair<const int, int> >") DW_AT_data_member_location (0x00) DW_AT_accessibility (DW_ACCESS_public) 0x00001a81: DW_TAG_subprogram DW_AT_name ("allocator") DW_AT_decl_file ("/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/bits/allocator.h") DW_AT_decl_line (163) DW_AT_declaration (true) DW_AT_external (true) DW_AT_accessibility (DW_ACCESS_public) 0x00001a86: DW_TAG_formal_parameter DW_AT_type (0x00002dd1 "std::allocator<std::pair<const int, int> > *") DW_AT_artificial (true) 0x00001a8b: NULL 0x00001a8c: DW_TAG_subprogram DW_AT_name ("allocator") DW_AT_decl_file ("/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/bits/allocator.h") DW_AT_decl_line (167) DW_AT_declaration (true) DW_AT_external (true) DW_AT_accessibility (DW_ACCESS_public) 0x00001a91: DW_TAG_formal_parameter DW_AT_type (0x00002dd1 "std::allocator<std::pair<const int, int> > *") DW_AT_artificial (true) 0x00001a96: DW_TAG_formal_parameter DW_AT_type (0x00002dd6 "const std::allocator<std::pair<const int, int> > &") 0x00001a9b: NULL 0x00001a9c: DW_TAG_subprogram DW_AT_linkage_name ("_ZNSaISt4pairIKiiEEaSERKS2_") DW_AT_name ("operator=") DW_AT_decl_file ("/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/bits/allocator.h") DW_AT_decl_line (172) DW_AT_type (0x00002de0 "std::allocator<std::pair<const int, int> > &") DW_AT_declaration (true) DW_AT_external (true) DW_AT_accessibility (DW_ACCESS_public) 0x00001aa6: DW_TAG_formal_parameter DW_AT_type (0x00002dd1 "std::allocator<std::pair<const int, int> > *") DW_AT_artificial (true) 0x00001aab: DW_TAG_formal_parameter DW_AT_type (0x00002dd6 "const std::allocator<std::pair<const int, int> > &") 0x00001ab0: NULL 0x00001ab1: DW_TAG_subprogram DW_AT_name ("~allocator") DW_AT_decl_file ("/usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/bits/allocator.h") DW_AT_decl_line (184) DW_AT_declaration (true) DW_AT_external (true) DW_AT_accessibility (DW_ACCESS_public) 0x00001ab6: DW_TAG_formal_parameter DW_AT_type (0x00002dd1 "std::allocator<std::pair<const int, int> > *") DW_AT_artificial (true) 0x00001abb: NULL ``` I propose to add fallback implementation based on type of `_M_h`.
diff --git a/lldb/examples/synthetic/gnu_libstdcpp.py b/lldb/examples/synthetic/gnu_libstdcpp.py
@@ -63,11 +63,8 @@ def __init__(self, valobj, dict):
         self.count = None
 
     def extract_type(self):
-        type = self.valobj.GetType()
-        # The last template argument is the allocator type.
-        template_arg_num = type.GetNumberOfTemplateArguments() - 1
-        allocator_type = type.GetTemplateArgumentType(template_arg_num)
-        data_type = allocator_type.GetTemplateArgumentType(0)
+        head_type = self.head.GetType().GetCanonicalType()
+        data_type = head_type.GetTemplateArgumentType(1)
         return data_type
 
     def update(self):
