[llvm] [llvm-gsymutil] Add option to load callsites from DWARF (PR #119913)

[Greg Clayton via llvm-commits]

================
@@ -553,6 +558,58 @@ void DwarfTransformer::handleDie(OutputAggregator &Out, CUInfo &CUI,
     handleDie(Out, CUI, ChildDie);
 }
 
+void DwarfTransformer::parseCallSiteInfoFromDwarf(CUInfo &CUI, DWARFDie Die,
+                                                  FunctionInfo &FI) {
+  // Parse all DW_TAG_call_site DIEs that are children of this subprogram DIE.
+  // DWARF specification:
+  // - DW_TAG_call_site can have DW_AT_call_return_pc for return address offset.
+  // - DW_AT_call_origin might point to a DIE of the function being called.
+  // For simplicity, we will just extract return_offset and possibly target name
+  // if available.
+
+  CallSiteInfoCollection CSIC;
+
+  for (DWARFDie Child : Die.children()) {
+    if (Child.getTag() != dwarf::DW_TAG_call_site)
+      continue;
+
+    CallSiteInfo CSI;
+    // DW_AT_call_return_pc: the return PC (address). We'll convert it to
+    // offset relative to FI's start.
+    auto ReturnPC = dwarf::toAddress(Child.find(dwarf::DW_AT_call_return_pc));
+    if (!ReturnPC || *ReturnPC < FI.startAddress() ||
+        *ReturnPC >= FI.endAddress())
+      continue;
+
+    CSI.ReturnOffset = *ReturnPC - FI.startAddress();
+
+    // Attempt to get function name from DW_AT_call_origin. If present, we can
+    // insert it as a match regex.
+    if (DWARFDie OriginDie =
+            Child.getAttributeValueAsReferencedDie(dwarf::DW_AT_call_origin)) {
+      if (auto Name = OriginDie.getName(DINameKind::ShortName)) {
----------------
clayborg wrote:

You might want the linkage name instead:
```
0x0000002d:   DW_TAG_subprogram
                DW_AT_linkage_name	("_Z3foov")
                DW_AT_name	("foo")
                DW_AT_decl_file	("/Users/gclayton/Documents/src/inlined/main.cpp")
                DW_AT_decl_line	(3)
                DW_AT_type	(0x0000000000000036 "int")
                DW_AT_external	(true)
                DW_AT_inline	(DW_INL_inlined)
```

Use `DWARFDie::getLinkageName()` first, and if that returns NULL, then use `DWARFDie::getShortName()`

https://github.com/llvm/llvm-project/pull/119913