From 6362a111d93556659edc837740167d62485081e0 Mon Sep 17 00:00:00 2001
From: Martin <laz.git@mfriebe.de>
Date: Mon, 21 Apr 2025 20:05:06 +0200
Subject: [PATCH] FpDebug: more DWARF-4 DW_FORM_exprloc and location-list
 handling (DW_FORM_sec_offset)

---
 components/fpdebug/fpdbgdwarf.pas            | 15 +++++++++++----
 components/fpdebug/fpdbgdwarfdataclasses.pas | 16 ++++++++++++++++
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/components/fpdebug/fpdbgdwarf.pas b/components/fpdebug/fpdbgdwarf.pas
index 9cdabb9f5e..5233d1eeaf 100644
--- a/components/fpdebug/fpdbgdwarf.pas
+++ b/components/fpdebug/fpdbgdwarf.pas
@@ -4588,13 +4588,17 @@ var
   InitLocParserData: TInitLocParserData;
   ByteSize: TFpDbgValueSize;
   BitOffset, BitSize: Int64;
+  IsLocList: Boolean;
 begin
   Result := True;
   if AnInformationEntry.GetAttribData(DW_AT_data_member_location, AttrData) then begin
     Form := AnInformationEntry.AttribForm[AttrData.Idx];
     Result := False;
 
-    if Form in [DW_FORM_data1, DW_FORM_data2, DW_FORM_sdata, DW_FORM_udata] then begin
+    IsLocList := DW_Form_IsLocationList(Form, CompilationUnit.Version);
+    if (not IsLocList) and
+       (Form in [DW_FORM_data1, DW_FORM_data2, DW_FORM_data4, DW_FORM_data8, DW_FORM_sdata, DW_FORM_udata])
+    then begin
       if AnInformationEntry.ReadValue(AttrData, ConstOffs) then begin
         {$PUSH}{$R-}{$Q-} // TODO: check overflow
         AnAddress.Address := AnAddress.Address + ConstOffs;
@@ -4605,10 +4609,9 @@ begin
         SetLastError(AValueObj, CreateError(fpErrAnyError));
     end
 
-    // TODO: loclistptr: DW_FORM_data4, DW_FORM_data8,
     else
-
-    if Form in [DW_FORM_block, DW_FORM_block1, DW_FORM_block2, DW_FORM_block4] then begin
+    if IsLocList or (Form in [DW_FORM_block, DW_FORM_block1, DW_FORM_block2, DW_FORM_block4, DW_FORM_exprloc])
+    then begin
       InitLocParserData.ObjectDataAddress := AnAddress;
       InitLocParserData.ObjectDataAddrPush := True;
       Result := LocationFromAttrData(AttrData, AValueObj, AnAddress, @InitLocParserData);
@@ -4881,8 +4884,12 @@ begin
   AnAddress := InvalidLoc;
 
   AForm :=  AnAttribData.InformationEntry.AttribForm[AnAttribData.Idx];
+  (* DW_FORM_data4, DW_FORM_data8 should only happen with DWARF-3 or before *)
   if (AForm = DW_FORM_data4) or (AForm = DW_FORM_data8) or (AForm = DW_FORM_sec_offset) then begin
     // location list
+    DebugLn((FPDBG_DWARF_VERBOSE or FPDBG_DWARF_WARNINGS or DBG_WARNINGS) and
+            (AForm in [DW_FORM_data4, DW_FORM_data8]) and (CompilationUnit.Version > 3),
+            ['Found location-list via DW_FORM_data# for newer DWARF version']);
     if not LocationExprFromLocationList(AnAttribData, AValueObj, Val) then begin
       DebugLn(FPDBG_DWARF_VERBOSE, ['LocationFromAttrData: failed to read DW_AT_location from loc-list']);
       if not IsError(AValueObj.LastError) then
diff --git a/components/fpdebug/fpdbgdwarfdataclasses.pas b/components/fpdebug/fpdbgdwarfdataclasses.pas
index 9dce993e88..d18835862f 100644
--- a/components/fpdebug/fpdbgdwarfdataclasses.pas
+++ b/components/fpdebug/fpdbgdwarfdataclasses.pas
@@ -949,6 +949,8 @@ function DbgsDump(AScope: TDwarfScopeInfo; ACompUnit: TDwarfCompilationUnit): St
 function GetDwarfSymbolClassMapList: TFpSymbolDwarfClassMapList; inline;
 function NameInfoForSearch(const AName: String): TNameSearchInfo;
 
+function DW_Form_IsLocationList(AForm: Cardinal; ADwarfVersion: integer): Boolean;
+
 property DwarfSymbolClassMapList: TFpSymbolDwarfClassMapList read GetDwarfSymbolClassMapList;
 
 implementation
@@ -979,6 +981,20 @@ begin
   Result.NameHash := objpas.Hash(Result.NameUpper) and $7fff or $8000;
 end;
 
+function DW_Form_IsLocationList(AForm: Cardinal; ADwarfVersion: integer): Boolean;
+begin
+  (* In DWARF V3 the forms DW_FORM_data4 and DW_FORM_data8 were members of either
+     class constant or one of the classes lineptr, loclistptr, macptr or rangelistptr,
+     depending on context.
+     In DWARF V4 DW_FORM_data4 and DW_FORM_data8 are members of class constant in all cases.
+     The new DW_FORM_sec_offset replaces their usage for the other classes.
+  *)
+  Result := (AForm = DW_FORM_sec_offset) or
+            ( (ADwarfVersion < 4) and
+              (AForm in [DW_FORM_data4, DW_FORM_data8])
+            );
+end;
+
 function Dbgs(AInfoData: Pointer; ACompUnit: TDwarfCompilationUnit): String;
 var
   Attrib: Pointer;