ZEBIN kernel _entry symbol update. (#15834)

_entry symbol with nonzero size is a nested function because it is
within the kernel symbol range. The implementation may cause some
problems for debugger. Updated the implementation to make _entry symbol
more like a label by changing its type to STT_NOTYPE and its size to 0.

Co-authored-by: Pete Chou <[email protected]>

Author: igcbot

IGC/Compiler/CISACodeGen/CISABuilder.cpp

@@ -6595,9 +6595,8 @@ namespace IGC
                 std::max(std::max(jitInfo->offsetToSkipPerThreadDataLoad,
                                   jitInfo->offsetToSkipCrossThreadDataLoad),
                          jitInfo->offsetToSkipSetFFIDGP1);
-            CreateLocalSymbol("_entry", vISA::GenSymType::S_FUNC, actual_kernel_start_off,
-                (unsigned)pMainKernel.getGenSize() - actual_kernel_start_off,
-                pOutput->m_symbols);
+            CreateLocalSymbol("_entry", vISA::GenSymType::S_NOTYPE,
+                actual_kernel_start_off, 0, pOutput->m_symbols);
 
             // Create local function symbols for direct stackcall functions.
             for (auto &stackFunc : stackFuncMap) {

IGC/ZEBinWriter/zebin/spec/elf.md

@@ -202,6 +202,6 @@ enum GenRelocType {
 In ZEBinary file for each kernel there is a corresponding ELF symbol with the
 same name as the kernel emitted in the .symtab. The kernel symbol is local and
 points to offset 0 of the section. Currently for each kernel a local symbol
-"_entry" is emitted to represent the actul kernel start. A kernel may start
-with some prolog code and it is useful to know the actual kernel start offset
-in some cases.
+"_entry" is emitted to represent the actual kernel start, and the symbol type is
+STT_NOTYPE and the size is 0. A kernel may start with some prolog code and it
+is useful to know the actual kernel start offset in some cases.