cmd/exception: support RISC-V compressed instruction

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@canonical.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>

diff --git a/cmd/riscv/exception.c b/cmd/riscv/exception.c
index 7a08061d12037554e98d45f1d179d887bab18411..db8d8af04834dc4c95ec5015d817e51980c52966 100644 (file)
--- 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>