arm: smh: Add option to detect semihosting
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>
diff --git a/arch/arm/lib/semihosting.c b/arch/arm/lib/semihosting.c
index 7595dbc..dbea2b0 100644
--- a/arch/arm/lib/semihosting.c
+++ b/arch/arm/lib/semihosting.c
@@ -20,6 +20,7 @@
#define SYSWRITE 0x05
#define SYSREAD 0x06
#define SYSREADC 0x07
+#define SYSISERROR 0x08
#define SYSSEEK 0x0A
#define SYSFLEN 0x0C
#define SYSERRNO 0x13
@@ -41,6 +42,26 @@
return result;
}
+#if CONFIG_IS_ENABLED(SEMIHOSTING_FALLBACK)
+static bool _semihosting_enabled = true;
+static bool try_semihosting = true;
+
+bool semihosting_enabled(void)
+{
+ if (try_semihosting) {
+ smh_trap(SYSERRNO, NULL);
+ try_semihosting = false;
+ }
+
+ return _semihosting_enabled;
+}
+
+void disable_semihosting(void)
+{
+ _semihosting_enabled = false;
+}
+#endif
+
/**
* smh_errno() - Read the host's errno
*