RISC-V: Add PT_RISCV_ATTRIBUTES and add it to PHDR.

We added PT_RISCV_ATTRIBUTES to program header to make
.riscv.attribute easier to find in dynamic loader or kernel.

Ref:
https://github.com/riscv/riscv-elf-psabi-doc/pull/71

ChangeLog:

bfd/

	* elfnn-riscv.c(RISCV_ATTRIBUTES_SECTION_NAME): New.
	(riscv_elf_additional_program_headers): Ditto.
	(riscv_elf_modify_segment_map): Ditto.
	(elf_backend_additional_program_headers): Ditto.
	(elf_backend_modify_segment_map): Ditto.
	(elf_backend_obj_attrs_section): Use RISCV_ATTRIBUTES_SECTION_NAME
	rather than string literal.

binutils/

	* readelf.c(get_riscv_segment_type): New.
	(get_segment_type): Handle EM_RISCV.

include/

	* elf/riscv.h (PT_RISCV_ATTRIBUTES): New.
	* testsuite/ld-elf/orphan-region.ld: Discard .riscv.attributes
	section for simplify testcase.
	* testsuite/ld-riscv-elf/attr-phdr.d: New.
	* testsuite/ld-riscv-elf/attr-phdr.s: Ditto.
	* testsuite/ld-riscv-elf/ld-riscv-elf.exp: Add attr-phdr to
	testcase.

bfd/elfnn-riscv.c

@@ -62,6 +62,8 @@
 #define ELF_MAXPAGESIZE			0x1000
 #define ELF_COMMONPAGESIZE		0x1000
 
+#define RISCV_ATTRIBUTES_SECTION_NAME ".riscv.attributes"
+
 /* RISC-V ELF linker hash entry.  */
 
 struct riscv_elf_link_hash_entry
@@ -5158,6 +5160,64 @@ riscv_elf_is_target_special_symbol (bfd *abfd, asymbol *sym)
 	  || _bfd_elf_is_local_label_name (abfd, sym->name));
 }
 
+static int
+riscv_elf_additional_program_headers (bfd *abfd,
+				      struct bfd_link_info *info ATTRIBUTE_UNUSED)
+{
+  asection *s;
+  int ret = 0;
+
+  /* See if we need a PT_RISCV_ATTRIBUTES segment.  */
+  if (bfd_get_section_by_name (abfd, RISCV_ATTRIBUTES_SECTION_NAME))
+    ++ret;
+
+  return ret;
+}
+
+static bool
+riscv_elf_modify_segment_map (bfd *abfd,
+			      struct bfd_link_info *info)
+{
+  asection *s;
+  struct elf_segment_map *m, **pm;
+  size_t amt;
+
+  /* If there is a .riscv.attributes section, we need a PT_RISCV_ATTRIBUTES
+     segment.  */
+  s = bfd_get_section_by_name (abfd, RISCV_ATTRIBUTES_SECTION_NAME);
+  if (s != NULL)
+    {
+      for (m = elf_seg_map (abfd); m != NULL; m = m->next)
+	if (m->p_type == PT_RISCV_ATTRIBUTES)
+	  break;
+      /* If there is already a PT_RISCV_ATTRIBUTES header, avoid adding
+	 another.  */
+      if (m == NULL)
+	{
+	  amt = sizeof (*m);
+	  m = bfd_zalloc (abfd, amt);
+	  if (m == NULL)
+	    return false;
+
+	  m->p_type = PT_RISCV_ATTRIBUTES;
+	  m->count = 1;
+	  m->sections[0] = s;
+
+	  /* We want to put it after the PHDR and INTERP segments.  */
+	  pm = &elf_seg_map (abfd);
+	  while (*pm != NULL
+		 && ((*pm)->p_type == PT_PHDR
+		     || (*pm)->p_type == PT_INTERP))
+	    pm = &(*pm)->next;
+
+	  m->next = *pm;
+	  *pm = m;
+	}
+    }
+
+  return true;
+}
+
 #define TARGET_LITTLE_SYM			riscv_elfNN_vec
 #define TARGET_LITTLE_NAME			"elfNN-littleriscv"
 #define TARGET_BIG_SYM				riscv_elfNN_be_vec
@@ -5190,6 +5250,9 @@ riscv_elf_is_target_special_symbol (bfd *abfd, asymbol *sym)
 #define elf_info_to_howto			riscv_info_to_howto_rela
 #define bfd_elfNN_bfd_relax_section		_bfd_riscv_relax_section
 #define bfd_elfNN_mkobject			elfNN_riscv_mkobject
+#define elf_backend_additional_program_headers \
+  riscv_elf_additional_program_headers
+#define elf_backend_modify_segment_map		riscv_elf_modify_segment_map
 
 #define elf_backend_init_index_section		_bfd_elf_init_1_index_section
 
@@ -5211,6 +5274,6 @@ riscv_elf_is_target_special_symbol (bfd *abfd, asymbol *sym)
 #undef  elf_backend_obj_attrs_section_type
 #define elf_backend_obj_attrs_section_type	SHT_RISCV_ATTRIBUTES
 #undef  elf_backend_obj_attrs_section
-#define elf_backend_obj_attrs_section		".riscv.attributes"
+#define elf_backend_obj_attrs_section		RISCV_ATTRIBUTES_SECTION_NAME
 
 #include "elfNN-target.h"

binutils/readelf.c

@@ -4094,6 +4094,16 @@ get_tic6x_segment_type (unsigned long type)
     }
 }
 
+static const char *
+get_riscv_segment_type (unsigned long type)
+{
+  switch (type)
+    {
+    case PT_RISCV_ATTRIBUTES: return "RISCV_ATTRIBUTES";
+    default:                  return NULL;
+    }
+}
+
 static const char *
 get_hpux_segment_type (unsigned long type, unsigned e_machine)
 {
@@ -4203,6 +4213,9 @@ get_segment_type (Filedata * filedata, unsigned long p_type)
 	    case EM_S390_OLD:
 	      result = get_s390_segment_type (p_type);
 	      break;
+	    case EM_RISCV:
+	      result = get_riscv_segment_type (p_type);
+	      break;
 	    default:
 	      result = NULL;
 	      break;

include/elf/riscv.h

@@ -120,6 +120,11 @@ END_RELOC_NUMBERS (R_RISCV_max)
 /* Additional section types.  */
 #define SHT_RISCV_ATTRIBUTES 0x70000003 /* Section holds attributes.  */
 
+/* Processor specific program header types.  */
+
+/* Location of RISC-V ELF attribute section. */
+#define PT_RISCV_ATTRIBUTES 0x70000003
+
 /* Object attributes.  */
 enum
 {

ld/testsuite/ld-elf/orphan-region.ld

@@ -7,5 +7,5 @@ SECTIONS
 {
 	.text : ALIGN (4) { *(.text) } > region
 	.rodata : ALIGN (4) { *(.rodata) } > region
-	/DISCARD/ : { *(.reginfo) *(.MIPS.abiflags) *(.trampolines) }
+	/DISCARD/ : { *(.reginfo) *(.MIPS.abiflags) *(.trampolines) *(.riscv.attributes) }
 }

ld/testsuite/ld-riscv-elf/attr-phdr.d

@@ -0,0 +1,19 @@
+#name: PT_RISCV_ATTRIBUTES check
+#source: attr-phdr.s
+#as: -march=rv32ic
+#ld: -m[riscv_choose_ilp32_emul]
+#readelf: -l
+
+Elf file type is EXEC \(Executable file\)
+Entry point .*
+There are .* program headers, starting at offset .*
+
+Program Headers:
+  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
+  RISCV_ATTRIBUT .*
+  LOAD           .*
+
+ Section to Segment mapping:
+  Segment Sections...
+   00     .riscv.attributes 
+   01     .text 

ld/testsuite/ld-riscv-elf/attr-phdr.s

@@ -0,0 +1,9 @@
+	.attribute arch, "rv32i2p0_m2p0"
+	.option nopic
+	.text
+	.align	1
+	.globl	_start
+	.type	_start, @function
+_start:
+	ret
+	.size	_start, .-_start

ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp

@@ -112,6 +112,7 @@ if [istarget "riscv*-*-*"] {
     run_dump_test "attr-merge-priv-spec-failed-04"
     run_dump_test "attr-merge-priv-spec-failed-05"
     run_dump_test "attr-merge-priv-spec-failed-06"
+    run_dump_test "attr-phdr"
     run_ld_link_tests [list \
 	[list "Weak reference 32" "-T weakref.ld -m[riscv_choose_ilp32_emul]" "" \
 	    "-march=rv32i -mabi=ilp32" {weakref32.s} \