vfs: add support for semihosting on ESP32-C3

components/riscv/include/riscv/semihosting.h

@@ -0,0 +1,68 @@
+/*
+ * SPDX-FileCopyrightText: 2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Perform semihosting call
+ *
+ * See https://github.com/riscv/riscv-semihosting-spec/ and the linked
+ * ARM semihosting spec for details.
+ *
+ * @param id    semihosting call number
+ * @param data  data block to pass to the host; number of items and their
+ *              meaning depends on the semihosting call. See the spec for
+ *              details.
+ *
+ * @return  return value from the host
+ */
+static inline long semihosting_call_noerrno(long id, long *data)
+{
+    register long a0 asm ("a0") = id;
+    register long a1 asm ("a1") = (long) data;
+    __asm__ __volatile__ (
+        ".option push\n"
+        ".option norvc\n"
+        "slli zero, zero, 0x1f\n"
+        "ebreak\n"
+        "srai zero, zero, 0x7\n"
+        ".option pop\n"
+        : "+r"(a0) : "r"(a1) : "memory");
+    return a0;
+}
+
+/**
+ * @brief Perform semihosting call and retrieve errno
+ *
+ * @param id    semihosting call number
+ * @param data  data block to pass to the host; number of items and their
+ *              meaning depends on the semihosting call. See the spec for
+ *              details.
+ * @param[out] out_errno  output, errno value from the host. Only set if
+ *                        the return value is negative.
+ * @return   return value from the host
+ */
+static inline long semihosting_call(long id, long *data, int *out_errno)
+{
+    long ret = semihosting_call_noerrno(id, data);
+    if (ret < 0) {
+        /* Constant also defined in openocd_semihosting.h,
+         * which is common for RISC-V and Xtensa; it is not included here
+         * to avoid a circular dependency.
+         */
+        const int semihosting_sys_errno = 0x13;
+        *out_errno = (int) semihosting_call_noerrno(semihosting_sys_errno, NULL);
+    }
+    return ret;
+}
+
+#ifdef __cplusplus
+}
+#endif