[RuntimeDyld] Ignore ST_FILE symbols when constructing GlobalSymbolTable

[loladiro]

Summary

ELF's STT_File symbols may overlap with regular globals in other files, so we should ignore them here in order to avoid having bogus entries in the symbol table that confuse us when resolving relocations.

[lhames]

LGTM. Thanks very much for catching this!

lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp

else {
   
       // Compute JIT symbol flags.
       JITSymbolFlags RTDyldSymFlags = JITSymbolFlags::None;
       if (Flags & SymbolRef::SF_Weak)
         RTDyldSymFlags |= JITSymbolFlags::Weak;
       if (Flags & SymbolRef::SF_Exported)
         RTDyldSymFlags |= JITSymbolFlags::Exported;
 
-      if (Flags & SymbolRef::SF_Absolute) {
+      if (Flags & SymbolRef::SF_Absolute &&
+          SymType != object::SymbolRef::ST_File) {
         auto Addr = I->getAddress();
         Check(Addr.getError());
         uint64_t SectOffset = *Addr;
         unsigned SectionID = AbsoluteSymbolSection;
 
         DEBUG(dbgs() << "\tType: " << SymType << " (absolute) Name: " << Name
                      << " SID: " << SectionID << " Offset: "
                      << format("%p", (uintptr_t)SectOffset)

test/ExecutionEngine/RuntimeDyld/X86/ELF_STT_FILE.s

+# RUN: llvm-mc -triple=x86_64-pc-linux -relocation-model=pic -filetype=obj -o %T/test_ELF_STT_FILE_FILE_x86-64.o %p/Inputs/ELF_STT_FILE_FILE.s
+# RUN: llvm-mc -triple=x86_64-pc-linux -relocation-model=pic -filetype=obj -o %T/test_ELF_STT_FILE_GLOBAL_x86-64.o %p/Inputs/ELF_STT_FILE_GLOBAL.s
+# RUN: llvm-mc -triple=x86_64-pc-linux -relocation-model=pic -filetype=obj -o %T/test_ELF_STT_FILE_x86-64.o %s
+# RUN: llvm-rtdyld -triple=x86_64-pc-linux -verify %T/test_ELF_STT_FILE_GLOBAL_x86-64.o %T/test_ELF_STT_FILE_FILE_x86-64.o %T/test_ELF_STT_FILE_x86-64.o
+
+# Test that RTDyldELF ignores STT_FILE symbols, and in particular does
+# crash if we are relocating against a symbol that happens to have the
+# same name as an STT_FILE symbol.
+
+_main:
+    movq    foo.c@GOTPCREL(%rip), %rax
+    movq    bar.c@GOTPCREL(%rip), %rax
+    movq    $0, %rax
+    retq

test/ExecutionEngine/RuntimeDyld/X86/Inputs/ELF_STT_FILE_FILE.s

+.file "foo.c"
+.global bar.c
+bar.c:

test/ExecutionEngine/RuntimeDyld/X86/Inputs/ELF_STT_FILE_GLOBAL.s

+.global foo.c
+foo.c: