[ARM] Emit Tag_conformance.

[• chatur01]

Summary

Emit the build attribute Tag_conformance.

Claim conformance to version 2.09 of the ARM ABI.

This build attribute must be emitted first amongst the build attributes when
written to an object file. This is to simplify conformance detection by
consumers.

[• chatur01]

Noticed a bug, sorry. Will prepare a new patch.

lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp

973–974

Will prepare a new revision here, I should be computing the length of the ConformanceValue string here, rather than assuming it will be a sane version number.

[• chatur01]

Review requested.

Fixed a bug in the computation of the conformance value length.

[t.p.northover]

Hi Charlie,

Couldn't this be achieved more simply by just changing the definition of AttributeItem::LessTag?

lib/Target/ARM/ARMAsmPrinter.cpp

834

Tiny niggle, but if this is going to be emitted first, why put this line here rather than at the beginning?

[• chatur01]

Thanks very much for reviewing Tim, your suggestion to modify the LessTag predicate cleaned this patch up a lot!

[t.p.northover]

Hi Charlie,

Thanks for updating the patch. This looks fine to me.

Tim.

[• chatur01]

Thanks Tim, committed r225166.

Kind regards,
Charlie.

lib/Target/ARM/ARMAsmPrinter.cpp

void ARMAsmPrinter::emitAttributes() {
   // for the wchar and enum size tags
   if (Subtarget->isR9Reserved())
       ATS.emitAttribute(ARMBuildAttrs::ABI_PCS_R9_use,
                         ARMBuildAttrs::R9Reserved);
   else
       ATS.emitAttribute(ARMBuildAttrs::ABI_PCS_R9_use,
                         ARMBuildAttrs::R9IsGPR);
 
+  ATS.emitTextAttribute(ARMBuildAttrs::conformance, "2.09");
+
   if (Subtarget->hasTrustZone() && Subtarget->hasVirtualization())
       ATS.emitAttribute(ARMBuildAttrs::Virtualization_use,
                         ARMBuildAttrs::AllowTZVirtualization);
   else if (Subtarget->hasTrustZone())
       ATS.emitAttribute(ARMBuildAttrs::Virtualization_use,
                         ARMBuildAttrs::AllowTZ);
   else if (Subtarget->hasVirtualization())
       ATS.emitAttribute(ARMBuildAttrs::Virtualization_use,

lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp

static bool LessTag(const AttributeItem &LHS, const AttributeItem &RHS) {
       return (LHS.Tag < RHS.Tag);
     }
   };
 
   StringRef CurrentVendor;
   unsigned FPU;
   unsigned Arch;
   unsigned EmittedArch;
+  // Tag_conformance must be special cased when emitted into an object
+  // file. See 2.3.7.4 of the Addenda to the ARM ABI document.
+  bool EmitConformance = false;
+  StringRef ConformanceValue;
+
   SmallVector<AttributeItem, 64> Contents;
 
   const MCSection *AttributeSection;
 
   AttributeItem *getAttributeItem(unsigned Attribute) {
     for (size_t i = 0; i < Contents.size(); ++i)
       if (Contents[i].Tag == Attribute)
         return &Contents[i];
AttributeItem Item = {
       Value,
       StringRef("")
     };
     Contents.push_back(Item);
   }
 
   void setAttributeItem(unsigned Attribute, StringRef Value,
                         bool OverwriteExisting) {
+    if (Attribute == ARMBuildAttrs::conformance) {
+      EmitConformance = true;
+      ConformanceValue = Value;
+      return;
+    }
+
     // Look for existing attribute item
     if (AttributeItem *Item = getAttributeItem(Attribute)) {
       if (!OverwriteExisting)
         return;
       Item->Type = AttributeItem::TextAttribute;
       Item->StringValue = Value;
       return;
     }
void ARMTargetELFStreamer::finishAttributeSection() {
   // ]*
 
   if (FPU != ARM::INVALID_FPU)
     emitFPUDefaultAttributes();
 
   if (Arch != ARM::INVALID_ARCH)
     emitArchDefaultAttributes();
 
-  if (Contents.empty())
+  if (Contents.empty() && !EmitConformance)
     return;
 
   std::sort(Contents.begin(), Contents.end(), AttributeItem::LessTag);
 
   ARMELFStreamer &Streamer = getStreamer();
 
   // Switch to .ARM.attributes section
   if (AttributeSection) {
void ARMTargetELFStreamer::finishAttributeSection() {
   }
 
   // Vendor size + Vendor name + '\0'
   const size_t VendorHeaderSize = 4 + CurrentVendor.size() + 1;
 
   // Tag + Tag Size
   const size_t TagHeaderSize = 1 + 4;
 
-  const size_t ContentsSize = calculateContentSize();
+  // + 6 for conformance tag (Tag (1) + 2.09 (4) + NB (1) = 6)
+  const size_t ContentsSize = calculateContentSize() + (EmitConformance ? 6 : 0);
 
   Streamer.EmitIntValue(VendorHeaderSize + TagHeaderSize + ContentsSize, 4);
   Streamer.EmitBytes(CurrentVendor);
   Streamer.EmitIntValue(0, 1); // '\0'
 
   Streamer.EmitIntValue(ARMBuildAttrs::File, 1);
   Streamer.EmitIntValue(TagHeaderSize + ContentsSize, 4);
 
+  if (EmitConformance) {
+    Streamer.EmitULEB128IntValue(67);
+    Streamer.EmitBytes(ConformanceValue);
+    Streamer.EmitIntValue(0, 1); // '\0
+  }
+
   // Size should have been accounted for already, now
   // emit each field as its type (ULEB or String)
   for (size_t i = 0; i < Contents.size(); ++i) {
     AttributeItem item = Contents[i];
     Streamer.EmitULEB128IntValue(item.Tag);
     switch (item.Type) {
     default: llvm_unreachable("Invalid attribute type");
     case AttributeItem::NumericAttribute:

test/CodeGen/ARM/build-attributes.ll

 
 ; V8:      .syntax unified
 ; V8: .eabi_attribute 6, 14
 ; V8-NOT:   .eabi_attribute 19
 ; V8: .eabi_attribute 20, 1
 ; V8: .eabi_attribute 21, 1
 ; V8-NOT: .eabi_attribute 22
 ; V8: .eabi_attribute 23, 3
+; V8: .eabi_attribute 67, "2.09"
 
 ; V8-FAST-NOT:   .eabi_attribute 19
 ;; The default does have an FPU, and for V8-A, it flushes preserving sign.
 ; V8-FAST: .eabi_attribute 20, 2
 ; V8-FAST-NOT: .eabi_attribute 21
 ; V8-FAST-NOT: .eabi_attribute 22
 ; V8-FAST: .eabi_attribute 23, 1
 

test/MC/ARM/directive-eabi_attribute.s

 @ RUN: llvm-mc -triple armv7-elf -filetype asm -o - %s | FileCheck %s
 @ RUN: llvm-mc < %s -triple armv7-unknown-linux-gnueabi -filetype=obj -o - \
 @ RUN:   | llvm-readobj -arm-attributes | FileCheck %s --check-prefix=CHECK-OBJ
 
         .syntax unified
         .thumb
 
+        .eabi_attribute Tag_conformance, "2.09"
+@ CHECK: .eabi_attribute 67, "2.09"
+@ Tag_conformance should be be emitted first in a file-scope
+@ sub-subsection of the first public subsection of the attributes
+@ section. 2.3.7.4 of ABI Addenda.
+@ CHECK-OBJ:        Tag: 67
+@ CHECK-OBJ-NEXT:   TagName: conformance
+@ CHECK-OBJ-NEXT:   Value: 2.09
   .eabi_attribute Tag_CPU_raw_name, "Cortex-A9"
 @ CHECK: .eabi_attribute 4, "Cortex-A9"
 @ CHECK-OBJ:        Tag: 4
 @ CHECK-OBJ-NEXT:   TagName: CPU_raw_name
 @ CHECK-OBJ-NEXT:   Value: Cortex-A9
   .eabi_attribute Tag_CPU_name, "cortex-a9"
 @ CHECK: .cpu cortex-a9
 @ CHECK-OBJ:        Tag: 5

 @ CHECK-OBJ-NEXT:   TagName: also_compatible_with
 @ CHECK-OBJ-NEXT:   Value: gnu
   .eabi_attribute Tag_T2EE_use, 0
 @ CHECK: .eabi_attribute 66, 0
 @ CHECK-OBJ:        Tag: 66
 @ CHECK-OBJ-NEXT:   Value: 0
 @ CHECK-OBJ-NEXT:   TagName: T2EE_use
 @ CHECK-OBJ-NEXT:   Description: Not Permitted
-  .eabi_attribute Tag_conformance, "2.09"
-@ CHECK: .eabi_attribute 67, "2.09"
-@ CHECK-OBJ:        Tag: 67
-@ CHECK-OBJ-NEXT:   TagName: conformance
-@ CHECK-OBJ-NEXT:   Value: 2.09
   .eabi_attribute Tag_Virtualization_use, 0
 @ CHECK: .eabi_attribute 68, 0
 @ CHECK-OBJ:        Tag: 68
 @ CHECK-OBJ-NEXT:   Value: 0
 @ CHECK-OBJ-NEXT:   TagName: Virtualization_use
 @ CHECK-OBJ-NEXT:   Description: Not Permitted
 
 @ ===--- Compatibility Checks ---===

test/tools/llvm-readobj/ARM/attribute-conformance.s

+@ RUN: llvm-mc -triple armv7-elf -filetype asm -o - %s | FileCheck %s
+@ RUN: llvm-mc -triple armv7-eabi -filetype obj -o - %s \
+@ RUN:   | llvm-readobj -arm-attributes - | FileCheck %s --check-prefix=CHECK-OBJ
+.eabi_attribute  Tag_conformance, "2.11"
+@CHECK:   .eabi_attribute 67, "2.11"
+@CHECK-OBJ: Tag: 67
+@CHECK-OBJ-NEXT: TagName: conformance
+@CHECK-OBJ-NEXT: Value: 2.11