[PATCH 1/1] cmd: exception: unaligned data access on RISC-V

[Rick Chen]

Hi Heinrich

> From: Heinrich Schuchardt [mailto:xypron.glpk at gmx.de]
> Sent: Tuesday, August 04, 2020 7:10 PM
> To: Rick Jian-Zhi Chen(陳建志)
> Cc: u-boot at lists.denx.de; Heinrich Schuchardt
> Subject: [PATCH 1/1] cmd: exception: unaligned data access on RISC-V
>
> The command 'exception' can be used to test the handling of exceptions.
>
> Currently the exception command only allows to create an illegal instruction exception on RISC-V.
>
> Provide a sub-command 'exception unaligned' to cause a misaligned load address exception.
>
> Adjust the online help for 'exception undefined'.
>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
> ---
>  cmd/riscv/exception.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/cmd/riscv/exception.c b/cmd/riscv/exception.c index 3c8dbbec0e..53159531d9 100644
> --- a/cmd/riscv/exception.c
> +++ b/cmd/riscv/exception.c
> @@ -8,6 +8,17 @@
>  #include <common.h>
>  #include <command.h>
>
> +static int do_unaligned(struct cmd_tbl *cmdtp, int flag, int argc,
> +                       char *const argv[])
> +{
> +       asm volatile (
> +               "auipc a1, 0\n"
> +               "ori   a1, a1, 3\n"
> +               "lw    a2, (0)(a1)\n"
> +       );
> +       return CMD_RET_FAILURE;

I suggest that we can modify it as below to print the unaligned
address and data for more debug information.

int ret = 0;
int addr = 0;

asm volatile (
"auipc a1, 0\n"
"ori   %0, a1, 3\n"
"lw    %1, (0)(a1)\n"
: "=r" (addr), "=r" (ret)
:
: "memory"
);
printf("unaligned addr 0x%x , ret 0x%x\n",addr,ret);

return CMD_RET_SUCCESS;
====================================
So if run in S-Mode, it will work as below:

RISC-V # exception unaligned
unaligned addr 0x3ff92fd7 , ret 0x35e59300
RISC-V #


(gdb) x/4x 0x3ff92fd0
0x3ff92fd0:     0x7ac362ef      0x00000597      0x0035e593      0xc5174190
(gdb)

====================================
If run in M-Mode, it will work as below:

RISC-V # exception unaligned
Unhandled exception: Load address misaligned
EPC: 000000003ff92fdc RA: 000000003ff93032 TVAL: 000000003ff92fd7
EPC: 0000000000009fdc RA: 000000000000a032 reloc adjusted

### ERROR ### Please RESET the board ###

Thanks,
Rick

> +}
> +
>  static int do_undefined(struct cmd_tbl *cmdtp, int flag, int argc,
>                         char *const argv[])
>  {
> @@ -16,6 +27,8 @@ static int do_undefined(struct cmd_tbl *cmdtp, int flag, int argc,  }
>
>  static struct cmd_tbl cmd_sub[] = {
> +       U_BOOT_CMD_MKENT(unaligned, CONFIG_SYS_MAXARGS, 1, do_unaligned,
> +                        "", ""),
>         U_BOOT_CMD_MKENT(undefined, CONFIG_SYS_MAXARGS, 1, do_undefined,
>                          "", ""),
>  };
> @@ -23,7 +36,8 @@ static struct cmd_tbl cmd_sub[] = {  static char exception_help_text[] =
>         "<ex>\n"
>         "  The following exceptions are available:\n"
> -       "  undefined  - undefined instruction\n"
> +       "  undefined - illegal instruction\n"
> +       "  unaligned - load address misaligned\n"
>         ;
>
>  #include <exception.h>
> --
> 2.27.0