[PATCH] RISC-V: Add RV32E support.

[Jim Wilson <jimw at sifive dot com>]

This adds support for the RV32E base architecture.  This is mostly work of
the Andes employees Kito Cheng and Monk Chiang.  I noticed during testing that
the patch didn't work right if multiple -march/-mabi options were used, and I
fixed it to properly clear and set flags.  I also updated the docs.

This was tested with binutils and gcc builds and checks both with and without
the new options -march=rv32e and -mabi=ilp32e.  There were no regressions.

Committed.

Jim

	Kito Cheng  <kito.cheng@gmail.com>
	Monk Chiang  <sh.chiang04@gmail.com>

	bfd/
	* elfnn-riscv.c (_bfd_riscv_elf_merge_private_bfd_data): Handle
	EF_RISCV_RVE.

	binutils/
	* readelf.c (get_machine_flags): Handle EF_RISCV_RVE.

	gas/
	* config/tc-riscv.c (rve_abi): New.
	(riscv_set_options): Add rve field.  Initialize it.
	(riscv_set_rve) New function.
	(riscv_set_arch): Support 'e' ISA subset.
	(reg_lookup_internal): If rve, check register is available.
	(riscv_set_abi): New parameter rve.
	(md_parse_option): Pass new argument to riscv_set_abi.
	(riscv_after_parse_args): Call riscv_set_rve.  If rve_abi, set
	EF_RISCV_RVE.
	* doc/c-riscv.texi (-mabi): Document new ilp32e argument.

	include/
	* elf/riscv.h (EF_RISCV_RVE): New define.
---
 bfd/elfnn-riscv.c     |  8 +++++++
 binutils/readelf.c    |  3 +++
 gas/config/tc-riscv.c | 66 +++++++++++++++++++++++++++++++++++++++++++--------
 gas/doc/c-riscv.texi  |  3 ++-
 include/elf/riscv.h   |  3 +++
 5 files changed, 72 insertions(+), 11 deletions(-)

diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
index b17c0e1000..b82e655b7b 100644
--- a/bfd/elfnn-riscv.c
+++ b/bfd/elfnn-riscv.c
@@ -2625,6 +2625,14 @@ _bfd_riscv_elf_merge_private_bfd_data (bfd *ibfd, struct bfd_link_info *info)
       goto fail;
     }
 
+  /* Disallow linking RVE and non-RVE.  */
+  if ((old_flags ^ new_flags) & EF_RISCV_RVE)
+    {
+      (*_bfd_error_handler)
+       (_("%pB: can't link RVE with other target"), ibfd);
+      goto fail;
+    }
+
   /* Allow linking RVC and non-RVC, and keep the RVC flag.  */
   elf_elfheader (obfd)->e_flags |= new_flags & EF_RISCV_RVC;
 
diff --git a/binutils/readelf.c b/binutils/readelf.c
index 6a9319f5db..8335538e03 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -3472,6 +3472,9 @@ get_machine_flags (Filedata * filedata, unsigned e_flags, unsigned e_machine)
 	  if (e_flags & EF_RISCV_RVC)
 	    strcat (buf, ", RVC");
 
+	  if (e_flags & EF_RISCV_RVE)
+	    strcat (buf, ", RVE");
+
 	  switch (e_flags & EF_RISCV_FLOAT_ABI)
 	    {
 	    case EF_RISCV_FLOAT_ABI_SOFT:
diff --git a/gas/config/tc-riscv.c b/gas/config/tc-riscv.c
index be32e6c979..43ae21fcb1 100644
--- a/gas/config/tc-riscv.c
+++ b/gas/config/tc-riscv.c
@@ -63,6 +63,7 @@ static const char default_arch[] = DEFAULT_ARCH;
 
 static unsigned xlen = 0; /* width of an x-register */
 static unsigned abi_xlen = 0; /* width of a pointer in the ABI */
+static bfd_boolean rve_abi = FALSE;
 
 #define LOAD_ADDRESS_INSN (abi_xlen == 64 ? "ld" : "lw")
 #define ADD32_INSN (xlen == 64 ? "addiw" : "addi")
@@ -75,6 +76,7 @@ struct riscv_set_options
 {
   int pic; /* Generate position-independent code.  */
   int rvc; /* Generate RVC code.  */
+  int rve; /* Generate RVE code.  */
   int relax; /* Emit relocs the linker is allowed to relax.  */
 };
 
@@ -82,6 +84,7 @@ static struct riscv_set_options riscv_opts =
 {
   0,	/* pic */
   0,	/* rvc */
+  0,	/* rve */
   1,	/* relax */
 };
 
@@ -94,6 +97,12 @@ riscv_set_rvc (bfd_boolean rvc_value)
   riscv_opts.rvc = rvc_value;
 }
 
+static void
+riscv_set_rve (bfd_boolean rve_value)
+{
+  riscv_opts.rve = rve_value;
+}
+
 struct riscv_subset
 {
   const char *name;
@@ -171,6 +180,16 @@ riscv_set_arch (const char *s)
       case 'i':
 	break;
 
+      case 'e':
+	p++;
+	riscv_add_subset ("e");
+	riscv_add_subset ("i");
+
+	if (xlen > 32)
+	  as_fatal ("-march=%s: rv%de is not a valid base ISA", s, xlen);
+
+	break;
+
       case 'g':
 	p++;
 	for ( ; *all_subsets != 'q'; all_subsets++)
@@ -181,7 +200,7 @@ riscv_set_arch (const char *s)
 	break;
 
       default:
-	as_fatal ("-march=%s: first ISA subset must be `i' or `g'", s);
+	as_fatal ("-march=%s: first ISA subset must be `e', `i' or `g'", s);
     }
 
   while (*p)
@@ -215,6 +234,18 @@ riscv_set_arch (const char *s)
 	as_fatal ("-march=%s: unsupported ISA subset `%c'", s, *p);
     }
 
+  if (riscv_subset_supports ("e") && riscv_subset_supports ("f"))
+    as_fatal ("-march=%s: rv32e does not support the `f' extension", s);
+
+  if (riscv_subset_supports ("d") && !riscv_subset_supports ("f"))
+    as_fatal ("-march=%s: `d' extension requires `f' extension", s);
+
+  if (riscv_subset_supports ("q") && !riscv_subset_supports ("d"))
+    as_fatal ("-march=%s: `q' extension requires `d' extension", s);
+
+  if (riscv_subset_supports ("q") && xlen < 64)
+    as_fatal ("-march=%s: rv32 does not support the `q' extension", s);
+
   free (extension);
 }
 
@@ -546,6 +577,10 @@ reg_lookup_internal (const char *s, enum reg_class class)
 
   if (r == NULL || DECODE_REG_CLASS (r) != class)
     return -1;
+
+  if (riscv_opts.rve && class == RCLASS_GPR && DECODE_REG_NUM (r) > 15)
+    return -1;
+
   return DECODE_REG_NUM (r);
 }
 
@@ -2165,10 +2200,11 @@ enum float_abi {
 static enum float_abi float_abi = FLOAT_ABI_DEFAULT;
 
 static void
-riscv_set_abi (unsigned new_xlen, enum float_abi new_float_abi)
+riscv_set_abi (unsigned new_xlen, enum float_abi new_float_abi, bfd_boolean rve)
 {
   abi_xlen = new_xlen;
   float_abi = new_float_abi;
+  rve_abi = rve;
 }
 
 int
@@ -2190,21 +2226,23 @@ md_parse_option (int c, const char *arg)
 
     case OPTION_MABI:
       if (strcmp (arg, "ilp32") == 0)
-	riscv_set_abi (32, FLOAT_ABI_SOFT);
+	riscv_set_abi (32, FLOAT_ABI_SOFT, FALSE);
+      else if (strcmp (arg, "ilp32e") == 0)
+	riscv_set_abi (32, FLOAT_ABI_SOFT, TRUE);
       else if (strcmp (arg, "ilp32f") == 0)
-	riscv_set_abi (32, FLOAT_ABI_SINGLE);
+	riscv_set_abi (32, FLOAT_ABI_SINGLE, FALSE);
       else if (strcmp (arg, "ilp32d") == 0)
-	riscv_set_abi (32, FLOAT_ABI_DOUBLE);
+	riscv_set_abi (32, FLOAT_ABI_DOUBLE, FALSE);
       else if (strcmp (arg, "ilp32q") == 0)
-	riscv_set_abi (32, FLOAT_ABI_QUAD);
+	riscv_set_abi (32, FLOAT_ABI_QUAD, FALSE);
       else if (strcmp (arg, "lp64") == 0)
-	riscv_set_abi (64, FLOAT_ABI_SOFT);
+	riscv_set_abi (64, FLOAT_ABI_SOFT, FALSE);
       else if (strcmp (arg, "lp64f") == 0)
-	riscv_set_abi (64, FLOAT_ABI_SINGLE);
+	riscv_set_abi (64, FLOAT_ABI_SINGLE, FALSE);
       else if (strcmp (arg, "lp64d") == 0)
-	riscv_set_abi (64, FLOAT_ABI_DOUBLE);
+	riscv_set_abi (64, FLOAT_ABI_DOUBLE, FALSE);
       else if (strcmp (arg, "lp64q") == 0)
-	riscv_set_abi (64, FLOAT_ABI_QUAD);
+	riscv_set_abi (64, FLOAT_ABI_QUAD, FALSE);
       else
 	return 0;
       break;
@@ -2247,6 +2285,11 @@ riscv_after_parse_args (void)
   else
     riscv_add_subset ("c");
 
+  /* Enable RVE if specified by the -march option.  */
+  riscv_set_rve (FALSE);
+  if (riscv_subset_supports ("e"))
+    riscv_set_rve (TRUE);
+
   /* Infer ABI from ISA if not specified on command line.  */
   if (abi_xlen == 0)
     abi_xlen = xlen;
@@ -2271,6 +2314,9 @@ riscv_after_parse_args (void)
 	}
     }
 
+  if (rve_abi)
+    elf_flags |= EF_RISCV_RVE;
+
   /* Insert float_abi into the EF_RISCV_FLOAT_ABI field of elf_flags.  */
   elf_flags |= float_abi * (EF_RISCV_FLOAT_ABI & ~(EF_RISCV_FLOAT_ABI << 1));
 }
diff --git a/gas/doc/c-riscv.texi b/gas/doc/c-riscv.texi
index 79bc4e37b6..045c33a3aa 100644
--- a/gas/doc/c-riscv.texi
+++ b/gas/doc/c-riscv.texi
@@ -46,7 +46,8 @@ Select the base isa, as specified by ISA.  For example -march=rv32ima.
 Selects the ABI, which is either "ilp32" or "lp64", optionally followed
 by "f", "d", or "q" to indicate single-precision, double-precision, or
 quad-precision floating-point calling convention, or none to indicate
-the soft-float calling convention.
+the soft-float calling convention.  Also, "ilp32" can optionally be followed
+by "e" to indicate the RVE ABI, which is always soft-float.
 
 @cindex @samp{-mrelax} option, RISC-V
 @item -mrelax
diff --git a/include/elf/riscv.h b/include/elf/riscv.h
index defbbf4c24..d036e83070 100644
--- a/include/elf/riscv.h
+++ b/include/elf/riscv.h
@@ -110,6 +110,9 @@ END_RELOC_NUMBERS (R_RISCV_max)
 /* File uses the quad-float ABI.  */
 #define EF_RISCV_FLOAT_ABI_QUAD 0x0006
 
+/* File uses the 32E base integer instruction.  */
+#define EF_RISCV_RVE 0x0008
+
 /* The name of the global pointer symbol.  */
 #define RISCV_GP_SYMBOL "__global_pointer$"
 
-- 
2.14.1