[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

974–975

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

843

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

static ARMBuildAttrs::CPUArch getArchForCPU(StringRef CPU,
   else
     return ARMBuildAttrs::v4;
 }
 
 void ARMAsmPrinter::emitAttributes() {
   MCTargetStreamer &TS = *OutStreamer.getTargetStreamer();
   ARMTargetStreamer &ATS = static_cast<ARMTargetStreamer &>(TS);
 
+  ATS.emitTextAttribute(ARMBuildAttrs::conformance, "2.09");
+
   ATS.switchVendor("aeabi");
 
   std::string CPUString = Subtarget->getCPUString();
 
   // FIXME: remove krait check when GNU tools support krait cpu
   if (CPUString != "generic" && CPUString != "krait")
     ATS.emitTextAttribute(ARMBuildAttrs::CPU_name, CPUString);
 
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);
 
   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,
                         ARMBuildAttrs::AllowVirtualization);

lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp

enum {
       TextAttribute,
       NumericAndTextAttributes
     } Type;
     unsigned Tag;
     unsigned IntValue;
     StringRef StringValue;
 
     static bool LessTag(const AttributeItem &LHS, const AttributeItem &RHS) {
-      return (LHS.Tag < RHS.Tag);
+      // The conformance tag must be emitted first when serialised
+      // into an object file. Specifically, the addenda to the ARM ABI
+      // states that (2.3.7.4):
+      //
+      // "To simplify recognition by consumers in the common case of
+      // claiming conformity for the whole file, this tag should be
+      // emitted first in a file-scope sub-subsection of the first
+      // public subsection of the attributes section."
+      //
+      // So it is special-cased in this comparison predicate when the
+      // attributes are sorted in finishAttributeSection().
+      return (RHS.Tag != ARMBuildAttrs::conformance) &&
+             ((LHS.Tag == ARMBuildAttrs::conformance) || (LHS.Tag < RHS.Tag));
     }
   };
 
   StringRef CurrentVendor;
   unsigned FPU;
   unsigned Arch;
   unsigned EmittedArch;
   SmallVector<AttributeItem, 64> Contents;
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();
 
   Streamer.EmitIntValue(VendorHeaderSize + TagHeaderSize + ContentsSize, 4);
   Streamer.EmitBytes(CurrentVendor);
   Streamer.EmitIntValue(0, 1); // '\0'
 
   Streamer.EmitIntValue(ARMBuildAttrs::File, 1);
   Streamer.EmitIntValue(TagHeaderSize + ContentsSize, 4);
 
   // Size should have been accounted for already, now

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-1.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, "0"
+@CHECK:   .eabi_attribute 67, "0"
+@CHECK-OBJ: Tag: 67
+@CHECK-OBJ-NEXT: TagName: conformance
+@CHECK-OBJ-NEXT: Value: 0

test/tools/llvm-readobj/ARM/attribute-conformance-2.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, "A.long--non numeric oddity...!!"
+@CHECK:   .eabi_attribute 67, "A.long--non numeric oddity...!!"
+@CHECK-OBJ: Tag: 67
+@CHECK-OBJ-NEXT: TagName: conformance
+@CHECK-OBJ-NEXT: Value: A.long--non numeric oddity...!!