ELF: Align RELRO to the target page size rather than the max page size.

[pcc]

Summary

If no bss sections appear after the relro segment, the loader will round
the r/w segment size to the target's page size. Align the relro size in the
same way to ensure that it does not extend past the end of the program's
own memory region.

lld/trunk/ELF/Writer.cpp

for (PhdrEntry &P : Phdrs) {
     }
     if (P.p_type == PT_LOAD)
       P.p_align = Config->MaxPageSize;
     else if (P.p_type == PT_GNU_RELRO) {
       P.p_align = 1;
       // The glibc dynamic loader rounds the size down, so we need to round up
       // to protect the last page. This is a no-op on FreeBSD which always
       // rounds up.
-      P.p_memsz = alignTo(P.p_memsz, Config->MaxPageSize);
+      P.p_memsz = alignTo(P.p_memsz, Target->PageSize);
     }
 
     // The TLS pointer goes after PT_TLS. At least glibc will align it,
     // so round up the size to make sure the offsets are correct.
     if (P.p_type == PT_TLS) {
       Out<ELFT>::TlsPhdr = &P;
       if (P.p_memsz)
         P.p_memsz = alignTo(P.p_memsz, P.p_align);

lld/trunk/test/ELF/aarch64-relro.s

+# RUN: llvm-mc -filetype=obj -triple=aarch64-unknown-freebsd %s -o %t
+# RUN: ld.lld %t -o %t2
+# RUN: llvm-readobj -program-headers %t2 | FileCheck %s
+
+# CHECK:      Type: PT_GNU_RELRO
+# CHECK-NEXT: Offset:
+# CHECK-NEXT: VirtualAddress:
+# CHECK-NEXT: PhysicalAddress:
+# CHECK-NEXT: FileSize:
+# CHECK-NEXT: MemSize: 4096
+
+.section .data.rel.ro,"aw",%progbits
+.byte 1