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.

6 files changed, 69 insertions, 1 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index de9ed2753bc..9f4ad7cbf25 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,11 @@
+2023-02-23  Fangrui Song  <i@maskray.me>
+
+	* 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.
+
 2023-02-20  Nick Clifton  <nickc@redhat.com>
 
 	PR 30004
diff --git a/ld/emultempl/riscvelf.em b/ld/emultempl/riscvelf.em
index b12d15065c4..bb6298d3e8d 100644
--- a/ld/emultempl/riscvelf.em
+++ b/ld/emultempl/riscvelf.em
@@ -25,6 +25,40 @@ fragment <<EOF
 #include "elf/riscv.h"
 #include "elfxx-riscv.h"
 
+static struct riscv_elf_params params = { .relax_gp = 1 };
+EOF
+
+# Define some shell vars to insert bits of code into the standard elf
+# parse_args and list_options functions.  */
+PARSE_AND_LIST_PROLOGUE=${PARSE_AND_LIST_PROLOGUE}'
+enum risccv_opt
+{
+  OPTION_RELAX_GP = 321,
+  OPTION_NO_RELAX_GP,
+};
+'
+
+PARSE_AND_LIST_LONGOPTS=${PARSE_AND_LIST_LONGOPTS}'
+    { "relax-gp", no_argument, NULL, OPTION_RELAX_GP },
+    { "no-relax-gp", no_argument, NULL, OPTION_NO_RELAX_GP },
+'
+
+PARSE_AND_LIST_OPTIONS=${PARSE_AND_LIST_OPTIONS}'
+  fprintf (file, _("  --relax-gp                  Perform GP relaxation\n"));
+  fprintf (file, _("  --no-relax-gp               Don'\''t perform GP relaxation\n"));
+'
+
+PARSE_AND_LIST_ARGS_CASES=${PARSE_AND_LIST_ARGS_CASES}'
+    case OPTION_RELAX_GP:
+      params.relax_gp = 1;
+      break;
+
+    case OPTION_NO_RELAX_GP:
+      params.relax_gp = 0;
+      break;
+'
+
+fragment <<EOF
 static void
 riscv_elf_before_allocation (void)
 {
@@ -96,6 +130,8 @@ riscv_create_output_section_statements (void)
 	       " whilst linking %s binaries\n"), "RISC-V");
       return;
     }
+
+  riscv_elf${ELFSIZE}_set_options (&link_info, &params);
 }
 
 EOF
diff --git a/ld/testsuite/ld-riscv-elf/code-model-relax-medlow-01-norelaxgp.d b/ld/testsuite/ld-riscv-elf/code-model-relax-medlow-01-norelaxgp.d
new file mode 100644
index 00000000000..8e40cc5f32d
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/code-model-relax-medlow-01-norelaxgp.d
@@ -0,0 +1,4 @@
+#source: code-model.s
+#as: -march=rv64i -mabi=lp64 --defsym __medlow__=1
+#ld: -Tcode-model-01.ld -melf64lriscv --no-relax-gp --relax
+#error: .*relocation truncated to fit: R_RISCV_HI20 against `symbolL'
diff --git a/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp b/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
index 0f7ccd92ed5..5dd6144efd3 100644
--- a/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
+++ b/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
@@ -122,6 +122,7 @@ if [istarget "riscv*-*-*"] {
     run_dump_test "align-small-region"
     run_dump_test "call-relax"
     run_dump_test "pcgp-relax-01"
+    run_dump_test "pcgp-relax-01-norelaxgp"
     run_dump_test "pcgp-relax-02"
     run_dump_test "c-lui"
     run_dump_test "c-lui-2"
@@ -141,6 +142,7 @@ if [istarget "riscv*-*-*"] {
     run_dump_test "code-model-medany-weakref-01"
     run_dump_test "code-model-medany-weakref-02"
     run_dump_test "code-model-relax-medlow-01"
+    run_dump_test "code-model-relax-medlow-01-norelaxgp"
     run_dump_test "code-model-relax-medlow-02"
     run_dump_test "code-model-relax-medlow-weakref-01"
     run_dump_test "code-model-relax-medlow-weakref-02"
diff --git a/ld/testsuite/ld-riscv-elf/pcgp-relax-01-norelaxgp.d b/ld/testsuite/ld-riscv-elf/pcgp-relax-01-norelaxgp.d
new file mode 100644
index 00000000000..d1344576ff3
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/pcgp-relax-01-norelaxgp.d
@@ -0,0 +1,18 @@
+#source: pcgp-relax-01.s
+#ld: --no-relax-gp --relax
+#objdump: -d -Mno-aliases
+
+.*:[ 	]+file format .*
+
+
+Disassembly of section \.text:
+
+0+[0-9a-f]+ <_start>:
+.*:[ 	]+[0-9a-f]+[ 	]+addi[ 	]+a0,a0,[0-9]+
+.*:[ 	]+[0-9a-f]+[ 	]+jal[ 	        ]+ra,[0-9a-f]+ <_start>
+.*:[ 	]+[0-9a-f]+[ 	]+auipc[ 	]+a1,0x[0-9a-f]+
+.*:[ 	]+[0-9a-f]+[ 	]+addi[ 	]+a1,a1,[0-9]+ # [0-9a-f]+ <data_g>
+.*:[ 	]+[0-9a-f]+[ 	]+lui[ 	        ]+a2,0x[0-9a-f]+
+.*:[ 	]+[0-9a-f]+[ 	]+addi[ 	]+a2,a2,[0-9]+ # [0-9a-f]+ <data_g>
+.*:[ 	]+[0-9a-f]+[ 	]+addi[ 	]+a3,tp,0 # 0 <data_t>
+.*:[ 	]+[0-9a-f]+[ 	]+auipc[ 	]+a0,0x[0-9a-f]+
diff --git a/ld/testsuite/ld-riscv-elf/pcgp-relax-02.d b/ld/testsuite/ld-riscv-elf/pcgp-relax-02.d
index 1248132ab42..055f03e57f2 100644
--- a/ld/testsuite/ld-riscv-elf/pcgp-relax-02.d
+++ b/ld/testsuite/ld-riscv-elf/pcgp-relax-02.d
@@ -1,6 +1,6 @@
 #source: pcgp-relax-02.s
 #as:
-#ld: --relax
+#ld: --relax --relax-gp
 #objdump: -d
 
 .*:[ 	]+file format .*