[ELF][LLD] Allow reading of more than one FEATURE_1_AND in same object.

[peter.smith]

Summary

This patch is a follow on from D62853 . Although many relocatable objects will have a single GNU_PROPERTY_X86_FEATURE_1_AND in the .note.gnu.property section it is permissible to have more than one, and there is a test in ld.bfd that uses it. The behavior that ld.bfd follows is to set the feature bit for a relocatable object if any of the GNU_PROPERTY_X86_FEATURE_1_AND have the feature bit set.

The specific test in ld.bfd is https://github.com/bminor/binutils-gdb/blob/master/ld/testsuite/ld-aarch64/property-bti-pac1.s there isn't an X86 equivalent test but the same behaviour can be observed with IBT and SHSTK. I've added a test case for that.

This could be considered a corner case, however it is not known whether tools will just add another GNU_PROPERTY_X86_FEATURE_1_AND rather than find an existing one and add to it.

[ruiu]

LGTM

lld/trunk/ELF/InputFiles.cpp

 // of zero or more type-length-value fields. We want to find a field of a
 // certain type. It seems a bit too much to just store a 32-bit value, perhaps
 // the ABI is unnecessarily complicated.
 template <class ELFT>
 static uint32_t readAndFeatures(ObjFile<ELFT> *Obj, ArrayRef<uint8_t> Data) {
   using Elf_Nhdr = typename ELFT::Nhdr;
   using Elf_Note = typename ELFT::Note;
 
+  uint32_t FeaturesSet = 0;
   while (!Data.empty()) {
     // Read one NOTE record.
     if (Data.size() < sizeof(Elf_Nhdr))
       fatal(toString(Obj) + ": .note.gnu.property: section too short");
 
     auto *Nhdr = reinterpret_cast<const Elf_Nhdr *>(Data.data());
     if (Data.size() < Nhdr->getSize())
       fatal(toString(Obj) + ": .note.gnu.property: section too short");
while (!Data.empty()) {
     while (!Desc.empty()) {
       if (Desc.size() < 8)
         fatal(toString(Obj) + ": .note.gnu.property: section too short");
 
       uint32_t Type = read32le(Desc.data());
       uint32_t Size = read32le(Desc.data() + 4);
 
       if (Type == GNU_PROPERTY_X86_FEATURE_1_AND) {
-        // We found the field.
-        return read32le(Desc.data() + 8);
+        // We found a FEATURE_1_AND field. There may be more than one of these
+        // in a .note.gnu.propery section, for a relocatable object we
+        // accumulate the bits set.
+        FeaturesSet |= read32le(Desc.data() + 8);
       }
 
       // On 64-bit, a payload may be followed by a 4-byte padding to make its
       // size a multiple of 8.
       if (ELFT::Is64Bits)
         Size = alignTo(Size, 8);
 
       Desc = Desc.slice(Size + 8); // +8 for Type and Size
     }
 
-    // Go to next NOTE record if a note section didn't contain
-    // X86_FEATURES_1_AND description.
+    // Go to next NOTE record to look for more FEATURE_1_AND descriptions.
     Data = Data.slice(Nhdr->getSize());
   }
 
-  return 0;
+  return FeaturesSet;
 }
 
 template <class ELFT>
 InputSectionBase *ObjFile<ELFT>::getRelocTarget(const Elf_Shdr &Sec) {
   uint32_t Idx = Sec.sh_info;
   if (Idx >= this->Sections.size())
     fatal(toString(this) + ": invalid relocated section index: " + Twine(Idx));
   InputSectionBase *Target = this->Sections[Idx];

lld/trunk/test/ELF/i386-cet.s

 # RUN: ld.lld -e func1 %t.o %t4.o -o %t
 # RUN: llvm-readelf -n %t | FileCheck -check-prefix=NOSHSTK -match-full-lines %s
 
 # Check .note.gnu.protery without property SHSTK.
 # NOSHSTK: Properties: x86 feature: IBT
 
 .section ".note.gnu.property", "a"
 .long 4
-.long 0x10
+.long 0xc
 .long 0x5
 .asciz "GNU"
 
 .long 0xc0000002
 .long 4
 .long 3
-.long 0
 
 .text
 .globl func1
 .type func1,@function
 func1:
   call func2
   ret

lld/trunk/test/ELF/x86-property-relocatable.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: ld.lld -r %t.o -o %t2.o
+# RUN: llvm-readelf -n %t2.o | FileCheck -match-full-lines %s
+
+## Test that .note.gnu.property is passed through -r, and that we can handle
+## more than one FEATURE_AND in the same object file. This is logically the
+## same as if the features were combined in a single FEATURE_AND as the rule
+## states that the bit in the output pr_data field if it is set in all
+.text
+ret
+
+.section ".note.gnu.property", "a"
+.p2align 3
+.long 4
+.long 0x10
+.long 0x5
+.asciz "GNU"
+
+.long 0xc0000002 // GNU_PROPERTY_X86_FEATURE_1_AND
+.long 4
+.long 1          // GNU_PROPERTY_X86_FEATURE_1_IBT
+.long 0
+
+.long 4
+.long 0x10
+.long 0x5
+.asciz "GNU"
+.long 0xc0000002 // GNU_PROPERTY_X86_FEATURE_1_AND
+.long 4
+.long 2          // GNU_PROPERTY_X86_FEATURE_1_SHSTK
+.long 0
+
+# CHECK:   Owner                 Data size  Description
+# CHECK-NEXT:   GNU                   0x00000010  NT_GNU_PROPERTY_TYPE_0 (property note)
+# CHECK-NEXT:     Properties:    x86 feature: IBT, SHSTK