RISC-V: Check multiletter extension has more than 1 letter

gcc/ChangeLog:

	* common/config/riscv/riscv-common.c
	(riscv_subset_list::parse_multiletter_ext): Checking multiletter
	extension has more than 1 letter.

gcc/testsuite/ChangeLog

	* gcc.target/riscv/arch-7.c: New.
	* gcc.target/riscv/attribute-10.c: Update test arch string.

1 files changed, 8 insertions, 0 deletions

diff --git a/gcc/common/config/riscv/riscv-common.c b/gcc/common/config/riscv/riscv-common.c
index b84503a7742..84695a6ed1b 100644
--- a/gcc/common/config/riscv/riscv-common.c
+++ b/gcc/common/config/riscv/riscv-common.c
@@ -524,6 +524,14 @@ riscv_subset_list::parse_multiletter_ext (const char *p,
 
       *q = '\0';
 
+      if (strlen (subset) == 1)
+	{
+	  error_at (m_loc, "%<-march=%s%>: name of %s must be more than 1 letter",
+		    m_arch, ext_type_str);
+	  free (subset);
+	  return NULL;
+	}
+
       add (subset, major_version, minor_version, explicit_version_p);
       free (subset);
       p += end_of_version - subset;