first semihosting integration

libwrap/semihosting/semihosting.c

@@ -0,0 +1,90 @@
+#include <stdint.h>
+#include <stdarg.h>
+#include <stddef.h>
+
+#include "semihosting.h"
+
+#define SEMIHOSTING_SYS_OPEN            0x01
+#define SEMIHOSTING_SYS_CLOSE           0x02
+#define SEMIHOSTING_SYS_WRITEC          0x03
+#define SEMIHOSTING_SYS_WRITE0          0x04
+#define SEMIHOSTING_SYS_WRITE           0x05
+#define SEMIHOSTING_SYS_READ            0x06
+#define SEMIHOSTING_SYS_READC           0x07
+#define SEMIHOSTING_SYS_ISERROR         0x08
+#define SEMIHOSTING_SYS_ISTTY           0x09
+#define SEMIHOSTING_SYS_SEEK            0x0A
+#define SEMIHOSTING_SYS_FLEN            0x0C
+#define SEMIHOSTING_SYS_TMPNAM          0x0D
+#define SEMIHOSTING_SYS_REMOVE          0x0E
+#define SEMIHOSTING_SYS_RENAME          0x0F
+#define SEMIHOSTING_SYS_CLOCK           0x10
+#define SEMIHOSTING_SYS_TIME            0x11
+#define SEMIHOSTING_SYS_SYSTEM          0x12
+#define SEMIHOSTING_SYS_ERRNO           0x13
+#define SEMIHOSTING_SYS_GET_CMDLINE     0x15
+#define SEMIHOSTING_SYS_HEAPINFO        0x16
+#define SEMIHOSTING_EnterSVC            0x17
+#define SEMIHOSTING_ReportException     0x18
+#define SEMIHOSTING_SYS_ELAPSED         0x30
+#define SEMIHOSTING_SYS_TICKFREQ        0x31
+
+#define RISCV_SEMIHOSTING_CALL_NUMBER 7
+
+
+static inline int __attribute__ ((always_inline)) call_host(int reason, void* arg) {
+#if 1
+    // This must always be set back to 0 to cover the case where a host wasn't
+    // initially present, but only connected while the program was already up and
+    // running. In that case, trap() suddenly won't be called anymore, so we have to
+    // clear this variable *before* EBREAK is called.
+    sh_missing_host = 0;
+
+    register int value asm ("a0") = reason;
+    register void* ptr asm ("a1") = arg;
+    asm volatile (
+        // Workaround for RISC-V lack of multiple EBREAKs.
+        " .option push \n"
+        " .option norvc \n"
+        // Force 16-byte alignment to make sure that the 3 instruction fall
+        // within the same virtual page. If you the instruction straddle a page boundary
+        // the debugger fetching the instructions could lead to a page fault.
+        // Note: align 4 means, align by 2 to the power of 4!
+        " .align 4 \n"
+        " slli x0, x0, 0x1f \n"
+        " ebreak \n"
+        " srai x0, x0, 0x07 \n"
+        " .option pop \n"
+
+        : "=r" (value) /* Outputs */
+        : "0" (value), "r" (ptr), [swi] "i" (RISCV_SEMIHOSTING_CALL_NUMBER) /* Inputs */
+        : "memory" /* Clobbers */
+    );
+    return value;
+#else
+    return 0;    
+#endif    
+}
+
+void sh_write0(const char* buf)
+{
+    // Print zero-terminated string
+    call_host(SEMIHOSTING_SYS_WRITE0, (void*) buf);
+}
+
+void sh_writec(char c)
+{
+    // Print single character
+    call_host(SEMIHOSTING_SYS_WRITEC, (void*)&c);
+}
+
+char sh_readc(void)
+{
+    // Read character from keyboard. (Blocking operation!)
+    char c = call_host(SEMIHOSTING_SYS_READC, (void*)NULL);
+
+    if (sh_missing_host)
+        return 0;
+    else
+        return c;
+}