RISC-V: Add --[no-]relax-gp to ld

--relax enables all relaxations.  --no-relax-gp disables GP relaxation to
allow measuring its effect.

The option can test effectiveness of GP relaxation and support some ABI
variants that use GP for other purposes.

Link: https://github.com/riscv-non-isa/riscv-elf-psabi-doc/issues/298

bfd/
    * elfnn-riscv.c (struct riscv_elf_link_hash_table): Add params.
    (riscv_elfNN_set_options): New.
    (riscv_info_to_howto_rela): Check relax_gp.
    (_bfd_riscv_relax_section): Likewise.
    * elfxx-riscv.h (struct riscv_elf_params): New.
    (riscv_elf32_set_options): New.
    (riscv_elf64_set_options): New.
ld/
    * emultempl/riscvelf.em: Add option parsing.
    * testsuite/ld-riscv-elf/code-model-relax-medlow-01-norelaxgp.d: New.
    * testsuite/ld-riscv-elf/pcgp-relax-01-norelaxgp.d: New.
    * testsuite/ld-riscv-elf/pcgp-relax-02.d: Test --relax --relax-gp can be
      used together.

3 files changed, 35 insertions, 2 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index b7c03c1..50e1e17 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,13 @@
+2023-02-23  Fangrui Song  <i@maskray.me>
+
+	* elfnn-riscv.c (struct riscv_elf_link_hash_table): Add params.
+	(riscv_elfNN_set_options): New.
+	(riscv_info_to_howto_rela): Check relax_gp.
+	(_bfd_riscv_relax_section): Likewise.
+	* elfxx-riscv.h (struct riscv_elf_params): New.
+	(riscv_elf32_set_options): New.
+	(riscv_elf64_set_options): New.
+
 2023-02-23  Nick Clifton  <nickc@redhat.com>
             Alan Modra  <amodra@gmail.com>
 
diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
index 355ddb2..1200e6b 100644
--- a/bfd/elfnn-riscv.c
+++ b/bfd/elfnn-riscv.c
@@ -118,6 +118,9 @@ struct riscv_elf_link_hash_table
 {
   struct elf_link_hash_table elf;
 
+  /* Various options and other info passed from the linker.  */
+  struct riscv_elf_params *params;
+
   /* Short-cuts to get to dynamic linker sections.  */
   asection *sdyntdata;
 
@@ -157,6 +160,13 @@ struct riscv_elf_link_hash_table
     && elf_hash_table_id (elf_hash_table (p)) == RISCV_ELF_DATA)	\
    ? (struct riscv_elf_link_hash_table *) (p)->hash : NULL)
 
+void
+riscv_elfNN_set_options (struct bfd_link_info *link_info,
+			 struct riscv_elf_params *params)
+{
+  riscv_elf_hash_table (link_info)->params = params;
+}
+
 static bool
 riscv_info_to_howto_rela (bfd *abfd,
 			  arelent *cache_ptr,
@@ -4389,7 +4399,9 @@ _bfd_riscv_relax_lui (bfd *abfd,
 		      bool undefined_weak)
 {
   bfd_byte *contents = elf_section_data (sec)->this_hdr.contents;
-  bfd_vma gp = riscv_global_pointer_value (link_info);
+  bfd_vma gp = riscv_elf_hash_table (link_info)->params->relax_gp
+		   ? riscv_global_pointer_value (link_info)
+		   : 0;
   int use_rvc = elf_elfheader (abfd)->e_flags & EF_RISCV_RVC;
 
   BFD_ASSERT (rel->r_offset + 4 <= sec->size);
@@ -4834,7 +4846,7 @@ _bfd_riscv_relax_section (bfd *abfd, asection *sec,
 		   || type == R_RISCV_TPREL_LO12_I
 		   || type == R_RISCV_TPREL_LO12_S)
 	    relax_func = _bfd_riscv_relax_tls_le;
-	  else if (!bfd_link_pic (info)
+	  else if (!bfd_link_pic (info) && htab->params->relax_gp
 		   && (type == R_RISCV_PCREL_HI20
 		       || type == R_RISCV_PCREL_LO12_I
 		       || type == R_RISCV_PCREL_LO12_S))
diff --git a/bfd/elfxx-riscv.h b/bfd/elfxx-riscv.h
index 5e1bdae..abcb409 100644
--- a/bfd/elfxx-riscv.h
+++ b/bfd/elfxx-riscv.h
@@ -27,6 +27,17 @@
 
 #define RISCV_UNKNOWN_VERSION -1
 
+struct riscv_elf_params
+{
+  /* Whether to relax code sequences to GP-relative addressing.  */
+  bool relax_gp;
+};
+
+extern void riscv_elf32_set_options (struct bfd_link_info *,
+				     struct riscv_elf_params *);
+extern void riscv_elf64_set_options (struct bfd_link_info *,
+				     struct riscv_elf_params *);
+
 extern reloc_howto_type *
 riscv_reloc_name_lookup (bfd *, const char *);