[ELF] Implement R_ARM_TARGET1

[davide]

Summary

I hit this relocation while building some software for ARM and realized the support for that is a little bit weird. In fact, TARGET1 is interpreted as REL32 or ABS32 depending on if --target1-rel or --target1-abs is passed on the cmdline. The default behaviour seems to interpret the relocation as ABS if no option is passed.

[ruiu]

ELF/Config.h

1 ↗

(On Diff #66211)

Revert.

ELF/Relocations.cpp

538 ↗

(On Diff #66211)

This affects all targets even though only ARM needs it. It is better to add cases for TARGET1 relocation to ARMTargetInfo::getRelExpr and ARMTargetInfo::relocateOne instead.

[davide]

Makes sense. Virtual calls are expensive, alas :( I also forgot to git add the test, should be in this revision.

[ruiu]

ELF/Target.cpp

1505 ↗

(On Diff #66229)

I think I'd prefer adding case R_ARM_TARGET1 to the following switches because, by doing so, you don't need to read this function to understand how we handle ARM relocations for all relocation types except TARGET1. See below.

1536 ↗

(On Diff #66229)

case R_ARM_TARGET1:
  return Config->Target1Rel ? R_PC : R_ABS;

1558 ↗

(On Diff #66229)

if (Type == R_ARM_TARGET1 && !Config->Target1Rel)
  return R_ARM_ABS32;

1641 ↗

(On Diff #66229)

Add case R_ARM_TARGET32: so that you can remove modifyARMReloc from this function.

1770 ↗

(On Diff #66229)

Ditto

[davide]

Rui's comments.

[ruiu]

LGTM

lld/trunk/ELF/Config.h

struct Configuration {
   bool Rela;
   bool Relocatable;
   bool SaveTemps;
   bool Shared;
   bool Static = false;
   bool StripAll;
   bool StripDebug;
   bool SysvHash = true;
+  bool Target1Rel;
   bool Threads;
   bool Trace;
   bool Verbose;
   bool WarnCommon;
   bool ZCombreloc;
   bool ZExecStack;
   bool ZNodelete;
   bool ZNow;

lld/trunk/ELF/Driver.cpp

void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->NoUndefinedVersion = Args.hasArg(OPT_no_undefined_version);
   Config->Pie = Args.hasArg(OPT_pie);
   Config->PrintGcSections = Args.hasArg(OPT_print_gc_sections);
   Config->Relocatable = Args.hasArg(OPT_relocatable);
   Config->SaveTemps = Args.hasArg(OPT_save_temps);
   Config->Shared = Args.hasArg(OPT_shared);
   Config->StripAll = Args.hasArg(OPT_strip_all);
   Config->StripDebug = Args.hasArg(OPT_strip_debug);
+  Config->Target1Rel = Args.hasArg(OPT_target1_rel);
   Config->Threads = Args.hasArg(OPT_threads);
   Config->Trace = Args.hasArg(OPT_trace);
   Config->Verbose = Args.hasArg(OPT_verbose);
   Config->WarnCommon = Args.hasArg(OPT_warn_common);
 
   Config->DynamicLinker = getString(Args, OPT_dynamic_linker);
   Config->Entry = getString(Args, OPT_entry);
   Config->Fini = getString(Args, OPT_fini, "_fini");

lld/trunk/ELF/Options.td

def start_lib: F<"start-lib">,
   HelpText<"Start a grouping of objects that should be treated as if they were together in an archive">;
 
 def strip_all: F<"strip-all">, HelpText<"Strip all symbols">;
 
 def strip_debug: F<"strip-debug">, HelpText<"Strip debugging information">;
 
 def sysroot: J<"sysroot=">, HelpText<"Set the system root">;
 
+def target1_rel: F<"target1-rel">, HelpText<"Interpret R_ARM_TARGET1 as R_ARM_REL32">;
+
+def target1_abs: F<"target1-abs">, HelpText<"Interpret R_ARM_TARGET1 as R_ARM_ABS32">;
+
 def threads: F<"threads">, HelpText<"Enable use of threads">;
 
 def trace: F<"trace">, HelpText<"Print the names of the input files">;
 
 def trace_symbol : J<"trace-symbol=">, HelpText<"Trace references to symbols">;
 
 def undefined: J<"undefined=">,
   HelpText<"Force undefined symbol during linking">;

lld/trunk/ELF/Target.cpp

case R_ARM_GOTOFF32:
     return R_GOTREL;
   case R_ARM_GOT_BREL:
     // GOT(S) + A - GOT_ORG
     return R_GOT_OFF;
   case R_ARM_GOT_PREL:
   case R_ARM_TLS_IE32:
     // GOT(S) + A - P
     return R_GOT_PC;
+  case R_ARM_TARGET1:
+    return Config->Target1Rel ? R_PC : R_ABS;
   case R_ARM_TLS_GD32:
     return R_TLSGD_PC;
   case R_ARM_TLS_LDM32:
     return R_TLSLD_PC;
   case R_ARM_BASE_PREL:
     // B(S) + A - P
     // FIXME: currently B(S) assumed to be .got, this may not hold for all
     // platforms.
     return R_GOTONLY_PC;
   case R_ARM_MOVW_PREL_NC:
   case R_ARM_MOVT_PREL:
   case R_ARM_PREL31:
   case R_ARM_REL32:
   case R_ARM_THM_MOVW_PREL_NC:
   case R_ARM_THM_MOVT_PREL:
     return R_PC;
   case R_ARM_TLS_LE32:
     return R_TLS;
   }
 }
 
 uint32_t ARMTargetInfo::getDynRel(uint32_t Type) const {
+  if (Type == R_ARM_TARGET1 && !Config->Target1Rel)
+    return R_ARM_ABS32;
   if (Type == R_ARM_ABS32)
     return Type;
   // Keep it going with a dummy value so that we can find more reloc errors.
   errorDynRel(Type);
   return R_ARM_ABS32;
 }
 
 void ARMTargetInfo::writeGotPlt(uint8_t *Buf, const SymbolBody &) const {
void ARMTargetInfo::relocateOne(uint8_t *Loc, uint32_t Type,
   case R_ARM_NONE:
     break;
   case R_ARM_ABS32:
   case R_ARM_BASE_PREL:
   case R_ARM_GOTOFF32:
   case R_ARM_GOT_BREL:
   case R_ARM_GOT_PREL:
   case R_ARM_REL32:
+  case R_ARM_TARGET1:
   case R_ARM_TLS_GD32:
   case R_ARM_TLS_IE32:
   case R_ARM_TLS_LDM32:
   case R_ARM_TLS_LDO32:
   case R_ARM_TLS_LE32:
     write32le(Loc, Val);
     break;
   case R_ARM_PREL31:
uint64_t ARMTargetInfo::getImplicitAddend(const uint8_t *Buf,
   default:
     return 0;
   case R_ARM_ABS32:
   case R_ARM_BASE_PREL:
   case R_ARM_GOTOFF32:
   case R_ARM_GOT_BREL:
   case R_ARM_GOT_PREL:
   case R_ARM_REL32:
+  case R_ARM_TARGET1:
   case R_ARM_TLS_GD32:
   case R_ARM_TLS_LDM32:
   case R_ARM_TLS_LDO32:
   case R_ARM_TLS_IE32:
   case R_ARM_TLS_LE32:
     return SignExtend64<32>(read32le(Buf));
   case R_ARM_PREL31:
     return SignExtend64<31>(read32le(Buf));

lld/trunk/test/ELF/arm-target1.s

+// REQUIRES: arm
+// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t.o
+// RUN: llvm-readobj -r %t.o | FileCheck %s --check-prefix=RELOC
+// RUN: ld.lld -shared %t.o -o %t2.so --target1-rel
+// RUN: llvm-objdump -t -d %t2.so | FileCheck %s \
+// RUN:   --check-prefix=RELATIVE
+// RUN: not ld.lld -shared %t.o -o %t3.so 2>&1 | FileCheck %s \
+// RUN:   --check-prefix=ABS
+
+// RELOC: Relocations [
+// RELOC:   .rel.text {
+// RELOC:     0x0 R_ARM_TARGET1 patatino 0x0
+// RELOC:   }
+// RELOC: ]
+
+.text
+  .word patatino(target1)
+  patatino:
+
+// RELATIVE: Disassembly of section .text:
+// RELATIVE: $d.0:
+// RELATIVE:     1000:       04 00 00 00     andeq   r0, r0, r4
+// RELATIVE: SYMBOL TABLE:
+// RELATIVE: 00001004         .text           00000000 patatino
+
+// ABS: can't create dynamic relocation R_ARM_TARGET1 against readonly segment