[PATCH 1/1] cmd/exception: support RISC-V compressed instruction

[Heinrich Schuchardt]

Eliminating the C extension on application processors is under
discussion.

Support emitting a compressed instruction. This will lead to an
illegal instruction exception if the C extension is not implemented.

For testing build qemu-riscv64_defconfig with CONFIG_RISCV_ISA_C=n
and run with

    qemu-system-riscv64 -M virt -bios u-boot -nographic -cpu rv64,c=false

    => exception compressed
    Unhandled exception: Illegal instruction
    EPC: 0000000087731708 RA: 000000008773fe44 TVAL: 0000000000004501
    EPC: 000000008001b708 RA: 0000000080029e44 reloc adjusted

    Code: 0b93 0000 0493 0000 0993 0000 f06f ccdf (4501)

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
---
 cmd/riscv/exception.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/cmd/riscv/exception.c b/cmd/riscv/exception.c
index 7a08061d12..db8d8af048 100644
--- a/cmd/riscv/exception.c
+++ b/cmd/riscv/exception.c
@@ -8,6 +8,15 @@
 #include <common.h>
 #include <command.h>
 
+static int do_compressed(struct cmd_tbl *cmdtp, int flag, int argc,
+			 char *const argv[])
+{
+	/* c.li a0, 0; c.li a0, 0 */
+	asm volatile (".long 0x45014501\n");
+	printf("The system supports compressed instructions.\n");
+	return CMD_RET_SUCCESS;
+}
+
 static int do_ebreak(struct cmd_tbl *cmdtp, int flag, int argc,
 			char *const argv[])
 {
@@ -35,6 +44,8 @@ static int do_undefined(struct cmd_tbl *cmdtp, int flag, int argc,
 }
 
 static struct cmd_tbl cmd_sub[] = {
+	U_BOOT_CMD_MKENT(compressed, CONFIG_SYS_MAXARGS, 1, do_compressed,
+			 "", ""),
 	U_BOOT_CMD_MKENT(ebreak, CONFIG_SYS_MAXARGS, 1, do_ebreak,
 			 "", ""),
 	U_BOOT_CMD_MKENT(unaligned, CONFIG_SYS_MAXARGS, 1, do_unaligned,
@@ -46,9 +57,10 @@ static struct cmd_tbl cmd_sub[] = {
 static char exception_help_text[] =
 	"<ex>\n"
 	"  The following exceptions are available:\n"
-	"  ebreak    - breakpoint\n"
-	"  undefined - illegal instruction\n"
-	"  unaligned - load address misaligned\n"
+	"  compressed - compressed instruction\n"
+	"  ebreak     - breakpoint\n"
+	"  undefined  - illegal instruction\n"
+	"  unaligned  - load address misaligned\n"
 	;
 
 #include <exception.h>
-- 
2.40.1