If a debugger is not attached to U-Boot, semihosting calls will raise a
synchronous abort exception. Try to catch this and disable semihosting
so we can e.g. use another uart if one is available. In the immediate
case, we return an error, since it is not always possible to check for
semihosting beforehand (debug uart, user-initiated load command, etc.)
We handle all possible semihosting instructions, which is probably
overkill. However, we do need to keep track of what instruction set
we're using so that we don't suppress an actual error.
A future enhancement could try to determine semihosting capability by
inspecting the processor state. There's an example of this at [1] for
RISC-V. The equivalent for ARM would inspect the monitor modei
enable/select bits of the DSCR. However, as the article notes, an
exception handler is still helpful in order to catch disconnected
debuggers.
[1] https://tomverbeure.github.io/2021/12/30/Semihosting-on-RISCV.html#avoiding-hangs-when-a-debugger-is-not-connected
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
These functions are intended to support detecting semihosting and
falling back gracefully to alternative implementations. The test starts
by making semihosting call. SYS_ERRNO is chosen because it should not
mutate any state. If this semihosting call results in an exception
(rather than being caught by the debugger), then the exception handler
should call disable_semihosting() and resume execution after the call.
Ideally, this would just be part of semihosting by default, and not a
separate config. However, to reduce space ARM SPL doesn't include
exception vectors by default. This means we can't detect if a
semihosting call failed unless we enable them. To avoid forcing them to
be enabled, we use a separate config option. It might also be possible
to try and detect whether a debugger has enabled (by reading HDE from
DSCR), but I wasn't able to figure out a way to do this from all ELs.
This patch just introduces the generic code to handle detection. The
next patch will implement it for arm64 (but not arm32).
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
This adds three wrappers around the semihosting commands for reading and
writing to the host console. We use the more standard getc/putc/puts
names instead of readc/writec/write0 for familiarity.
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
In order to add filesystem support, we will need to be able to seek and
write files. Add the appropriate helper functions.
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
There's no point in using string constants for smh_open if we are just
going to have to parse them. Instead, use numeric modes. The user needs
to be a bit careful with these, since they are much closer semantically
to string modes used by fopen(3) than the numeric modes used with
open(2).
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
This exports semihosting functions for use in other files. The header is
in include/ and not arm/include/asm because I anticipate that RISC-V may
want to add their own implementation at some point.
smh_len_fd has been renamed to smh_flen to more closely match the
semihosting spec.
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
