[PATCH 1/6] cmd: exception: arm64: fix undefined, add faults

[Heinrich Schuchardt]

On 1/9/22 18:30, Andre Przywara wrote:
> The arm64 version of the exception command was just defining the
> undefined exception, but actually copied the AArch32 instruction.
> 
> Replace that with an encoding that is guaranteed to be and stay
> undefined. Also add instructions to trigger unaligned access faults and
> a breakpoint.
> This brings ARM64 on par with ARM(32) for the exception command.
> 
> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
> ---
>   cmd/arm/exception64.c | 42 ++++++++++++++++++++++++++++++++++++++----
>   1 file changed, 38 insertions(+), 4 deletions(-)
> 
> diff --git a/cmd/arm/exception64.c b/cmd/arm/exception64.c
> index d5de50a0803..1a9730e6aec 100644
> --- a/cmd/arm/exception64.c
> +++ b/cmd/arm/exception64.c
> @@ -12,14 +12,46 @@ static int do_undefined(struct cmd_tbl *cmdtp, int flag, int argc,
>   			char *const argv[])
>   {
>   	/*
> -	 * 0xe7f...f.	is undefined in ARM mode
> -	 * 0xde..	is undefined in Thumb mode
> +	 * Instructions starting with the upper 16 bits all 0 are permanently
> +	 * undefined. The lower 16 bits can be used for some kind of immediate.
> +	 * --- ARMv8 ARM (ARM DDI 0487G.a C6.2.339: "UDF")

What is the title and URL of the document? I could not find it. It would 
be good to add this information in the comments.

Best regards

Heinrich

>   	 */
> -	asm volatile (".word 0xe7f7defb\n");
> +	asm volatile (".word 0x00001234\n");
> +
> +	return CMD_RET_FAILURE;
> +}
> +
> +static int do_unaligned(struct cmd_tbl *cmdtp, int flag, int argc,
> +			char *const argv[])
> +{
> +	/*
> +	 * The load acquire instruction requires the data source to be
> +	 * naturally aligned, and will fault even if strict alignment fault
> +	 * checking is disabled.
> +	 * --- ARMv8 ARM (ARM DDI 0487G.a B2.5.2: "Alignment of data accesses")
> +	 */
> +	asm volatile (
> +		"mov	x1, sp\n\t"
> +		"orr	x1, x1, #3\n\t"
> +		"ldar	x0, [x1]\n"
> +		::: "x0", "x1" );
> +
> +	return CMD_RET_FAILURE;
> +}
> +
> +static int do_breakpoint(struct cmd_tbl *cmdtp, int flag, int argc,
> +			 char *const argv[])
> +{
> +	asm volatile ("brk	#123\n");
> +
>   	return CMD_RET_FAILURE;
>   }
>   
>   static struct cmd_tbl cmd_sub[] = {
> +	U_BOOT_CMD_MKENT(breakpoint, CONFIG_SYS_MAXARGS, 1, do_breakpoint,
> +			 "", ""),
> +	U_BOOT_CMD_MKENT(unaligned, CONFIG_SYS_MAXARGS, 1, do_unaligned,
> +			 "", ""),
>   	U_BOOT_CMD_MKENT(undefined, CONFIG_SYS_MAXARGS, 1, do_undefined,
>   			 "", ""),
>   };
> @@ -27,7 +59,9 @@ static struct cmd_tbl cmd_sub[] = {
>   static char exception_help_text[] =
>   	"<ex>\n"
>   	"  The following exceptions are available:\n"
> -	"  undefined  - undefined instruction\n"
> +	"  breakpoint - breakpoint instruction exception\n"
> +	"  unaligned  - unaligned LDAR data abort\n"
> +	"  undefined  - undefined instruction exception\n"
>   	;
>   
>   #include <exception.h>