[Sparc] Include __tls_get_addr in symbol table for TLS calls to it

[jrtc27]

Summary

Global Dynamic and Local Dynamic call relocations only implicitly
reference __tls_get_addr; there is no connection in the ELF file between
the relocations and the symbol other than the specification for the
relocations' semantics. However, it still needs to be in the symbol
table despite the lack of explicit references to the symbol table entry,
since it needs to be bound at link time for these relocations, otherwise
any objects will fail to link. For details, see
https://sourceware.org/bugzilla/show_bug.cgi?id=22832.

[JDevlieghere]

A small nit but otherwise no objections from my part.

lib/Target/Sparc/MCTargetDesc/SparcMCExpr.cpp

198

Could you make this comment a little more concise and move the rest of the explanation/motivation (as well as the link to the PR) part of the commit message?

[jrtc27]

Shortened comment, moving description to commit message as requested

[JDevlieghere]

LGTM! Let me know if you want me to commit this for you.

[glaubitz]

Cool, thank you! \o/

Hope to see it in 6.0 as well :).

[jrtc27]

In D43271#1012975, @JDevlieghere wrote:

LGTM! Let me know if you want me to commit this for you.

Please do; thanks!

lib/Target/Sparc/MCTargetDesc/SparcMCExpr.cpp

case MCExpr::Unary:
     break;
   }
 
 }
 
 void SparcMCExpr::fixELFSymbolsInTLSFixups(MCAssembler &Asm) const {
   switch(getKind()) {
   default: return;
+  case VK_Sparc_TLS_GD_CALL:
+  case VK_Sparc_TLS_LDM_CALL: {
+    // The corresponding relocations reference __tls_get_addr, as they call it,
+    // but this is only implicit; there is no connection in the ELF file
+    // between the relocation and the symbol, other than the specification for
+    // the semantics of the relocations. However, the symbol must be included
+    // in our symbol table despite the lack of references to it, since it needs
+    // to be bound during linking for these relocations. For details see
+    // https://sourceware.org/bugzilla/show_bug.cgi?id=22832.
+    MCSymbol *Symbol = Asm.getContext().getOrCreateSymbol("__tls_get_addr");
+    Asm.registerSymbol(*Symbol);
+    auto ELFSymbol = cast<MCSymbolELF>(Symbol);
+    if (!ELFSymbol->isBindingSet()) {
+      ELFSymbol->setBinding(ELF::STB_GLOBAL);
+      ELFSymbol->setExternal(true);
+    }
+    LLVM_FALLTHROUGH;
+  }
   case VK_Sparc_TLS_GD_HI22:
   case VK_Sparc_TLS_GD_LO10:
   case VK_Sparc_TLS_GD_ADD:
-  case VK_Sparc_TLS_GD_CALL:
   case VK_Sparc_TLS_LDM_HI22:
   case VK_Sparc_TLS_LDM_LO10:
   case VK_Sparc_TLS_LDM_ADD:
-  case VK_Sparc_TLS_LDM_CALL:
   case VK_Sparc_TLS_LDO_HIX22:
   case VK_Sparc_TLS_LDO_LOX10:
   case VK_Sparc_TLS_LDO_ADD:
   case VK_Sparc_TLS_IE_HI22:
   case VK_Sparc_TLS_IE_LO10:
   case VK_Sparc_TLS_IE_LD:
   case VK_Sparc_TLS_IE_LDX:
   case VK_Sparc_TLS_IE_ADD:

test/CodeGen/SPARC/tls.ll

 ; RUN: llc <%s -march=sparc   -relocation-model=static | FileCheck %s --check-prefix=v8abs
 ; RUN: llc <%s -march=sparcv9 -relocation-model=static | FileCheck %s --check-prefix=v9abs
 ; RUN: llc <%s -march=sparc   -relocation-model=pic    | FileCheck %s --check-prefix=pic
 ; RUN: llc <%s -march=sparcv9 -relocation-model=pic    | FileCheck %s --check-prefix=pic
 
-; RUN: llc <%s -march=sparc   -relocation-model=static -filetype=obj | llvm-readobj -r | FileCheck %s --check-prefix=v8abs-obj
-; RUN: llc <%s -march=sparcv9 -relocation-model=static -filetype=obj | llvm-readobj -r | FileCheck %s --check-prefix=v9abs-obj
-; RUN: llc <%s -march=sparc   -relocation-model=pic    -filetype=obj | llvm-readobj -r | FileCheck %s --check-prefix=pic-obj
-; RUN: llc <%s -march=sparcv9 -relocation-model=pic    -filetype=obj | llvm-readobj -r | FileCheck %s --check-prefix=pic-obj
+; RUN: llc <%s -march=sparc   -relocation-model=static -filetype=obj | llvm-readobj -r -t | FileCheck %s --check-prefix=v8abs-obj
+; RUN: llc <%s -march=sparcv9 -relocation-model=static -filetype=obj | llvm-readobj -r -t | FileCheck %s --check-prefix=v9abs-obj
+; RUN: llc <%s -march=sparc   -relocation-model=pic    -filetype=obj | llvm-readobj -r -t | FileCheck %s --check-prefix=pic-obj
+; RUN: llc <%s -march=sparcv9 -relocation-model=pic    -filetype=obj | llvm-readobj -r -t | FileCheck %s --check-prefix=pic-obj
 
 @local_symbol = internal thread_local global i32 0
 @extern_symbol = external thread_local global i32
 
 ; v8abs-LABEL:  test_tls_local
 ; v8abs:        sethi  %tle_hix22(local_symbol), [[R0:%[goli][0-7]]]
 ; v8abs:        xor    [[R0]], %tle_lox10(local_symbol), [[R1:%[goli][0-7]]]
 ; v8abs:        ld     [%g7+[[R1]]]

 ; pic-obj:    0x{{[0-9,A-F]+}} R_SPARC_TLS_LDO_ADD local_symbol 0x0
 ; pic-obj:    0x{{[0-9,A-F]+}} R_SPARC_PC22 _GLOBAL_OFFSET_TABLE_ 0x4
 ; pic-obj:    0x{{[0-9,A-F]+}} R_SPARC_PC10 _GLOBAL_OFFSET_TABLE_ 0x8
 ; pic-obj:    0x{{[0-9,A-F]+}} R_SPARC_TLS_GD_HI22 extern_symbol 0x0
 ; pic-obj:    0x{{[0-9,A-F]+}} R_SPARC_TLS_GD_LO10 extern_symbol 0x0
 ; pic-obj:    0x{{[0-9,A-F]+}} R_SPARC_TLS_GD_ADD extern_symbol 0x0
 ; pic-obj:    0x{{[0-9,A-F]+}} R_SPARC_TLS_GD_CALL extern_symbol 0x0
 ; pic-obj: ]
+; pic-obj:      Symbols [
+; pic-obj:        Symbol {
+; pic-obj:          Name: __tls_get_addr ({{[0-9]+}})
+; pic-obj-NEXT:     Value: 0x0
+; pic-obj-NEXT:     Size: 0
+; pic-obj-NEXT:     Binding: Global (0x1)
+; pic-obj-NEXT:     Type: None (0x0)
+; pic-obj-NEXT:     Other: 0
+; pic-obj-NEXT:     Section: Undefined (0x0)
+; pic-obj-NEXT:   }
+; pic-obj:      ]