[ARM] Emit correct build attributes for the different relocation models

[rmaprath]

Summary

Generate build attributes:

1. Tag_ABI_PCS_RW_data
2. Tag_ABI_PCS_RO_data
3. Tag_ABI_PCS_GOT_use

Based on the selected relocation model.

[t.p.northover]

Hi Asiri,

The code looks correct to me, from what I understand of the ABI. I've just got one issue with the comments

Cheers.

Tim.

include/llvm/Support/ARMBuildAttributes.h

150–151

I think the comments are misleading: the point is that compatible objects *must* use PCRel or SBRel addressing, not that they can if they want to.

I was confused until I looked at the actual ABI addendum.

[aemerson]

Thanks Tim. I've committed Asiri's modified patch in r209656.

include/llvm/Support/ARMBuildAttributes.h

   AllowNeon2 = 2,     // SIMDv2 was permitted (Half-precision FP, MAC operations)
   AllowNeonARMv8 = 3, // ARM v8-A SIMD was permitted
 
+  // Tag_ABI_PCS_RW_data, (=15), uleb128
+  AddressRWPCRel = 1, // Permit PC-relative addressing of RW static data
+  AddressRWSBRel = 2, // Permit SB-relative addressing of RW static data
+  AddressRWNone = 3, // No RW static data permitted
+
+  // Tag_ABI_PCS_RO_data, (=14), uleb128
+  AddressROPCRel = 1, // Permit PC-relative addressing of RO static data
+  AddressRONone = 2, // No RO static data permitted
+
+  // Tag_ABI_PCS_GOT_use, (=17), uleb128
+  AddressDirect = 1, // Address imported data directly
+  AddressGOT = 2, // Address imported data indirectly (via GOT)
+
   // Tag_ABI_FP_denormal, (=20), uleb128
   PreserveFPSign = 2, // sign when flushed-to-zero is preserved
 

lib/Target/ARM/ARMAsmPrinter.cpp

       ATS.emitFPU(ARM::VFPV2);
   }
 
+  if (TM.getRelocationModel() == Reloc::PIC_) {
+    // PIC specific attributes.
+    ATS.emitAttribute(ARMBuildAttrs::ABI_PCS_RW_data,
+                      ARMBuildAttrs::AddressRWPCRel);
+    ATS.emitAttribute(ARMBuildAttrs::ABI_PCS_RO_data,
+                      ARMBuildAttrs::AddressROPCRel);
+    ATS.emitAttribute(ARMBuildAttrs::ABI_PCS_GOT_use,
+                      ARMBuildAttrs::AddressGOT);
+  } else {
+    // Allow direct addressing of imported data for all other relocation models.
+    ATS.emitAttribute(ARMBuildAttrs::ABI_PCS_GOT_use,
+                      ARMBuildAttrs::AddressDirect);
+  }
+
   // Signal various FP modes.
   if (!TM.Options.UnsafeFPMath) {
     ATS.emitAttribute(ARMBuildAttrs::ABI_FP_denormal, ARMBuildAttrs::Allowed);

test/CodeGen/ARM/build-attributes.ll

 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=-vfp2,-vfp3,-vfp4,-neon | FileCheck %s --check-prefix=CORTEX-A7-NOFPU
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=+vfp4,-neon | FileCheck %s --check-prefix=CORTEX-A7-FPUV4
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=+vfp4,,+d16,-neon | FileCheck %s --check-prefix=CORTEX-A7-FPUV4
+; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=pic | FileCheck %s --check-prefix=RELOC-PIC
+; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=static | FileCheck %s --check-prefix=RELOC-OTHER
+; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=default | FileCheck %s --check-prefix=RELOC-OTHER
+; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=dynamic-no-pic | FileCheck %s --check-prefix=RELOC-OTHER
+; RUN: llc < %s -mtriple=arm-none-linux-gnueabi | FileCheck %s --check-prefix=RELOC-OTHER
 
 ; XSCALE:      .eabi_attribute 6, 5
 ; XSCALE:      .eabi_attribute 8, 1

 ; CORTEX-A57-NOT:  .eabi_attribute 44
 ; CORTEX-A57:  .eabi_attribute 68, 3
 
+; RELOC-PIC:  .eabi_attribute 15, 1
+; RELOC-PIC:  .eabi_attribute 16, 1
+; RELOC-PIC:  .eabi_attribute 17, 2
+; RELOC-OTHER:  .eabi_attribute 17, 1
+
 define i32 @f(i64 %z) {
   ret i32 0
 }