[PATCH 12/13] riscv: gas: Add command line option '-mcpu=' to specify the CPU

[Christoph Muellner <christoph.muellner@vrull.eu>]

From: Christoph Müllner <christoph.muellner@vrull.eu>

There are devices in the field, that need a quite long
"-march="-argument to specify the available ISA extensions.
Let's introduce a pretty-name mechanism for them, so they have
a more user-friendly way to enable their ISA extensions.

Restrictions for this new -mcpu= flag are:
* the provided CPU name must be known (otherwise we bail out)
* mixing with -march is possible, but the last cmdln argument wins
  (i.e. no merging)

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
---
 gas/config/tc-riscv.c                       | 33 +++++++++++++++++++++
 gas/doc/c-riscv.texi                        |  6 ++++
 gas/testsuite/gas/riscv/mcpu-fail-unknown.d |  3 ++
 gas/testsuite/gas/riscv/mcpu-fail-unknown.l |  2 ++
 4 files changed, 44 insertions(+)
 create mode 100644 gas/testsuite/gas/riscv/mcpu-fail-unknown.d
 create mode 100644 gas/testsuite/gas/riscv/mcpu-fail-unknown.l

diff --git a/gas/config/tc-riscv.c b/gas/config/tc-riscv.c
index e89e9f492d9..22109e5912f 100644
--- a/gas/config/tc-riscv.c
+++ b/gas/config/tc-riscv.c
@@ -3476,6 +3476,7 @@ const char *md_shortopts = "O::g::G:";
 enum options
 {
   OPTION_MARCH = OPTION_MD_BASE,
+  OPTION_MCPU,
   OPTION_PIC,
   OPTION_NO_PIC,
   OPTION_MABI,
@@ -3495,6 +3496,7 @@ enum options
 struct option md_longopts[] =
 {
   {"march", required_argument, NULL, OPTION_MARCH},
+  {"mcpu", required_argument, NULL, OPTION_MCPU},
   {"fPIC", no_argument, NULL, OPTION_PIC},
   {"fpic", no_argument, NULL, OPTION_PIC},
   {"fno-pic", no_argument, NULL, OPTION_NO_PIC},
@@ -3514,6 +3516,33 @@ struct option md_longopts[] =
 };
 size_t md_longopts_size = sizeof (md_longopts);
 
+struct riscv_cpu_option_table
+{
+  const char *name;
+  const char *arch;
+};
+
+/* This table maps a CPU name (for -mcpu=$name) to the corresponding
+   arch string.  */
+static const struct riscv_cpu_option_table riscv_cpus[] = {
+  { NULL, NULL }
+};
+
+/* Returns the arch for the provided CPU name, or NULL if not known.  */
+static const char*
+get_riscv_arch_for_cpu(const char* mcpu)
+{
+  const struct riscv_cpu_option_table *cpu;
+
+  for (cpu = &riscv_cpus[0]; cpu->name; cpu++)
+    {
+      if (!strcmp(cpu->name, mcpu))
+	return cpu->arch;
+    }
+  as_bad (_("unknown CPU `%s'"), mcpu);
+  return NULL;
+}
+
 int
 md_parse_option (int c, const char *arg)
 {
@@ -3523,6 +3552,10 @@ md_parse_option (int c, const char *arg)
       default_arch_with_ext = arg;
       break;
 
+    case OPTION_MCPU:
+      default_arch_with_ext = get_riscv_arch_for_cpu(arg);
+      break;
+
     case OPTION_NO_PIC:
       riscv_opts.pic = false;
       break;
diff --git a/gas/doc/c-riscv.texi b/gas/doc/c-riscv.texi
index cc63760cb80..488f88791d1 100644
--- a/gas/doc/c-riscv.texi
+++ b/gas/doc/c-riscv.texi
@@ -46,6 +46,12 @@ Select the base isa, as specified by ISA.  For example -march=rv32ima.
 If this option and the architecture attributes aren't set, then assembler
 will check the default configure setting --with-arch=ISA.
 
+@cindex @samp{-mcpu=CPU} option, RISC-V
+@item -mcpu=CPU
+This option specifies the target processor.  The assembler will issue an error
+message if an attempt is made to assemble an instruction which will not execute
+on the target processor.
+
 @cindex @samp{-misa-spec=ISAspec} option, RISC-V
 @item -misa-spec=ISAspec
 Select the default isa spec version.  If the version of ISA isn't set
diff --git a/gas/testsuite/gas/riscv/mcpu-fail-unknown.d b/gas/testsuite/gas/riscv/mcpu-fail-unknown.d
new file mode 100644
index 00000000000..8afe43632d8
--- /dev/null
+++ b/gas/testsuite/gas/riscv/mcpu-fail-unknown.d
@@ -0,0 +1,3 @@
+#as: -mcpu=foo
+#source: empty.s
+#error_output: mcpu-fail-unknown.l
diff --git a/gas/testsuite/gas/riscv/mcpu-fail-unknown.l b/gas/testsuite/gas/riscv/mcpu-fail-unknown.l
new file mode 100644
index 00000000000..dccca4fb42d
--- /dev/null
+++ b/gas/testsuite/gas/riscv/mcpu-fail-unknown.l
@@ -0,0 +1,2 @@
+.*Assembler messages:
+.*Error: .*unknown CPU `foo'
-- 
2.37.2