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cmd/exception: support RISC-V compressed instruction

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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>
This commit is contained in:
Heinrich Schuchardt
2023-09-21 10:42:18 +02:00
committed by Leo Yu-Chi Liang
parent c202426d6a
commit f2e4b9d3c2
1 changed files with 15 additions and 3 deletions
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18
cmd/riscv/exception.c
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@@ -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>