x86-64: Allocate input section memory if needed

When --no-keep-memory is used, the input section memory may not be cached.
Allocate input section memory for -z pack-relative-relocs if needed.

bfd/

	PR ld/29939
	* elfxx-x86.c (elf_x86_size_or_finish_relative_reloc): Allocate
	input section memory if needed.

ld/

	PR ld/29939
	* testsuite/ld-elf/dt-relr-2i.d: New test.

bfd/elfxx-x86.c

@@ -1541,12 +1541,33 @@ elf_x86_size_or_finish_relative_reloc
 		    }
 		  else
 		    {
+		      bfd_byte *contents;
+
 		      if (rel.r_offset >= sec->size)
 			abort ();
+
+		      if (elf_section_data (sec)->this_hdr.contents
+			  != NULL)
+			contents
+			  = elf_section_data (sec)->this_hdr.contents;
+		      else
+			{
+			  if (!bfd_malloc_and_get_section (sec->owner,
+							   sec,
+							   &contents))
+			    info->callbacks->einfo
+			      /* xgettext:c-format */
+			      (_("%F%P: %pB: failed to allocate memory for section `%pA'\n"),
+			       info->output_bfd, sec);
+
+			  /* Cache the section contents for
+			     elf_link_input_bfd.  */
+			  elf_section_data (sec)->this_hdr.contents
+			    = contents;
+			}
 		      htab->elf_write_addend
 			(info->output_bfd, outrel->r_addend,
-			 (elf_section_data (sec)->this_hdr.contents
-			  + rel.r_offset));
+			 contents + rel.r_offset);
 		    }
 		}
 	    }

ld/testsuite/ld-elf/dt-relr-2i.d

@@ -0,0 +1,17 @@
+#source: dt-relr-2.s
+#ld: -e _start -pie --no-keep-memory $DT_RELR_LDFLAGS
+#readelf: -rW -d
+#target: [supports_dt_relr]
+
+#...
+ 0x[0-9a-f]+ \(RELR\)    +0x[0-9a-f]+
+ 0x[0-9a-f]+ \(RELRSZ\)  +(8|16) \(bytes\)
+ 0x[0-9a-f]+ \(RELRENT\) +(4|8) \(bytes\)
+#...
+Relocation section '\.rel(a|)\.dyn' at offset 0x[0-9a-f]+ contains 1 entry:
+#...
+[0-9a-f]+ +[0-9a-f]+ +R_.*_(RELATIVE|UADDR.*) .*
+#...
+Relocation section '\.relr\.dyn' at offset 0x[0-9a-f]+ contains 2 entries:
+  4 offsets
+#pass