[PATCH] D66925: [PPC32] Emit R_PPC_GOT_TPREL16 instead R_PPC_GOT_TPREL16_LO

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: adalava, hfinkel, jhibbits, jsji.
Herald added subscribers: llvm-commits, kbarton, nemanjai.
Herald added a project: LLVM.

Unlike ppc64, which has ADDISgotTprelHA+LDgotTprelL pairs,
ppc32 just uses LDgotTprelL32, so it does not make lots of sense to use
_LO without a paired _HA.

Emit R_PPC_GOT_TPREL16 instead R_PPC_GOT_TPREL16_LO to match GCC, and
get better linker relocation check. Note, R_PPC_GOT_TPREL16_{HA,LO}
don't have good linker support:

(a) lld does not support R_PPC_GOT_TPREL16_{HA,LO}.
(b) Top of tree ld.bfd does not support R_PPC_GOT_REL16_HA Initial-Exec -> Local-Exec relaxation:

  // a.o
  addis 3, 3, tsd_tls at got@tprel at ha
  lwz 3, tsd_tls at got@tprel at l(3)
  add 3, 3, tsd_tls at tls
  // b.o
  .section .tdata,"awT"; .globl tsd_tls; tsd_tls:
  
  // ld/ld-new a.o b.o
  internal error, aborting at ../../bfd/elf32-ppc.c:7952 in ppc_elf_relocate_section


Repository:
  rL LLVM

https://reviews.llvm.org/D66925

Files:
  lib/Target/PowerPC/PPCAsmPrinter.cpp
  test/CodeGen/PowerPC/tls.ll


Index: test/CodeGen/PowerPC/tls.ll
===================================================================
--- test/CodeGen/PowerPC/tls.ll
+++ test/CodeGen/PowerPC/tls.ll
@@ -43,7 +43,7 @@
 ;OPT0-PPC32-LABEL:    main2:
 ;OPT0-PPC32:       li [[REG1:[0-9]+]], _GLOBAL_OFFSET_TABLE_ at l
 ;OPT0-PPC32:       addis [[REG1]], [[REG1]], _GLOBAL_OFFSET_TABLE_ at ha
-;OPT0-PPC32:       lwz [[REG2:[0-9]+]], a2 at got@tprel at l([[REG1]])
+;OPT0-PPC32:       lwz [[REG2:[0-9]+]], a2 at got@tprel([[REG1]])
 ;OPT0-PPC32:       add 3, [[REG2]], a2 at tls
 
 ;OPT0-PPC32-PIC-LABEL:  main2:
@@ -51,4 +51,4 @@
 ;OPT0-PPC32-PIC-NOT:    li {{[0-9]+}}, _GLOBAL_OFFSET_TABLE_ at l
 ;OPT0-PPC32-PIC-NOT:    addis {{[0-9]+}}, {{[0-9+]}}, _GLOBAL_OFFSET_TABLE_ at ha
 ;OPT0-PPC32-PIC-NOT:    bl __tls_get_addr(a2 at tlsgd)@PLT
-;OPT0-PPC32-PIC:        lwz {{[0-9]+}}, a2 at got@tprel at l({{[0-9]+}})
+;OPT0-PPC32-PIC:        lwz {{[0-9]+}}, a2 at got@tprel({{[0-9]+}})
Index: lib/Target/PowerPC/PPCAsmPrinter.cpp
===================================================================
--- lib/Target/PowerPC/PPCAsmPrinter.cpp
+++ lib/Target/PowerPC/PPCAsmPrinter.cpp
@@ -870,8 +870,10 @@
     const GlobalValue *GValue = MO.getGlobal();
     MCSymbol *MOSymbol = getSymbol(GValue);
     const MCExpr *Exp =
-      MCSymbolRefExpr::create(MOSymbol, MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO,
-                              OutContext);
+        MCSymbolRefExpr::create(MOSymbol,
+                                isPPC64 ? MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO
+                                        : MCSymbolRefExpr::VK_PPC_GOT_TPREL,
+                                OutContext);
     TmpInst.getOperand(1) = MCOperand::createExpr(Exp);
     EmitToStreamer(*OutStreamer, TmpInst);
     return;


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