target/riscv: add semihosting support

- use the semihosting_common code
- to enable it, use the same commands as for arm

Signed-off-by: Liviu Ionescu <ilg@livius.net>

src/target/Makefile.am

@@ -141,6 +141,7 @@ RISCV_SRC = \
 	%D%/riscv/riscv-011.c \
 	%D%/riscv/riscv-013.c \
 	%D%/riscv/riscv.c \
+	%D%/riscv/riscv_semihosting.c \
 	%D%/riscv/program.c \
 	%D%/riscv/batch.c
 

src/target/riscv/riscv-011.c

@@ -1873,6 +1873,12 @@ static int handle_halt(struct target *target, bool announce)
 		riscv_enumerate_triggers(target);
 	}
 
+	if (target->debug_reason == DBG_REASON_BREAKPOINT) {
+		int retval;
+		if (riscv_semihosting(target, &retval) != 0)
+			return retval;
+	}
+
 	if (announce)
 		target_call_event_callbacks(target, TARGET_EVENT_HALTED);
 

src/target/riscv/riscv.c

@@ -263,6 +263,8 @@ static int riscv_init_target(struct command_context *cmd_ctx,
 	select_dbus.num_bits = target->tap->ir_length;
 	select_idcode.num_bits = target->tap->ir_length;
 
+	riscv_semihosting_init(target);
+
 	return ERROR_OK;
 }
 
@@ -1071,6 +1073,13 @@ int riscv_openocd_poll(struct target *target)
 	}
 
 	target->state = TARGET_HALTED;
+
+	if (target->debug_reason == DBG_REASON_BREAKPOINT) {
+		int retval;
+		if (riscv_semihosting(target, &retval) != 0)
+			return retval;
+	}
+
 	target_call_event_callbacks(target, TARGET_EVENT_HALTED);
 	return ERROR_OK;
 }
@@ -1515,6 +1524,43 @@ static const struct command_registration riscv_exec_command_handlers[] = {
 	COMMAND_REGISTRATION_DONE
 };
 
+extern __COMMAND_HANDLER(handle_common_semihosting_command);
+extern __COMMAND_HANDLER(handle_common_semihosting_fileio_command);
+extern __COMMAND_HANDLER(handle_common_semihosting_resumable_exit_command);
+extern __COMMAND_HANDLER(handle_common_semihosting_cmdline);
+
+static const struct command_registration arm_exec_command_handlers[] = {
+	{
+		"semihosting",
+		.handler = handle_common_semihosting_command,
+		.mode = COMMAND_EXEC,
+		.usage = "['enable'|'disable']",
+		.help = "activate support for semihosting operations",
+	},
+	{
+		"semihosting_cmdline",
+		.handler = handle_common_semihosting_cmdline,
+		.mode = COMMAND_EXEC,
+		.usage = "arguments",
+		.help = "command line arguments to be passed to program",
+	},
+	{
+		"semihosting_fileio",
+		.handler = handle_common_semihosting_fileio_command,
+		.mode = COMMAND_EXEC,
+		.usage = "['enable'|'disable']",
+		.help = "activate support for semihosting fileio operations",
+	},
+	{
+		"semihosting_resexit",
+		.handler = handle_common_semihosting_resumable_exit_command,
+		.mode = COMMAND_EXEC,
+		.usage = "['enable'|'disable']",
+		.help = "activate support for semihosting resumable exit",
+	},
+	COMMAND_REGISTRATION_DONE
+};
+
 const struct command_registration riscv_command_handlers[] = {
 	{
 		.name = "riscv",
@@ -1523,6 +1569,13 @@ const struct command_registration riscv_command_handlers[] = {
 		.usage = "",
 		.chain = riscv_exec_command_handlers
 	},
+	{
+		.name = "arm",
+		.mode = COMMAND_ANY,
+		.help = "ARM Command Group",
+		.usage = "",
+		.chain = arm_exec_command_handlers
+	},
 	COMMAND_REGISTRATION_DONE
 };
 

src/target/riscv/riscv.h

@@ -257,4 +257,7 @@ int riscv_remove_watchpoint(struct target *target,
 
 int riscv_init_registers(struct target *target);
 
+void riscv_semihosting_init(struct target *target);
+int riscv_semihosting(struct target *target, int *retval);
+
 #endif

src/target/riscv/riscv_semihosting.c

@@ -0,0 +1,194 @@
+/***************************************************************************
+ *   Copyright (C) 2018 by Liviu Ionescu                                   *
+ *   ilg@livius.net                                                        *
+ *                                                                         *
+ *   Copyright (C) 2009 by Marvell Technology Group Ltd.                   *
+ *   Written by Nicolas Pitre <nico@marvell.com>                           *
+ *                                                                         *
+ *   Copyright (C) 2010 by Spencer Oliver                                  *
+ *   spen@spen-soft.co.uk                                                  *
+ *                                                                         *
+ *   Copyright (C) 2016 by Square, Inc.                                    *
+ *   Steven Stallion <stallion@squareup.com>                               *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ *   This program is distributed in the hope that it will be useful,       *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU General Public License for more details.                          *
+ *                                                                         *
+ *   You should have received a copy of the GNU General Public License     *
+ *   along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ ***************************************************************************/
+
+/**
+ * @file
+ * Hold RISC-V semihosting support.
+ *
+ * The RISC-V code is inspired from ARM semihosting.
+ *
+ * Details can be found in chapter 8 of DUI0203I_rvct_developer_guide.pdf
+ * from ARM Ltd.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "log.h"
+
+#include "target/target.h"
+#include "target/semihosting_common.h"
+#include "riscv.h"
+
+static int riscv_semihosting_setup(struct target *target, int enable);
+static int riscv_semihosting_post_result(struct target *target);
+
+/**
+ * Initialize RISC-V semihosting. Use common ARM code.
+ */
+void riscv_semihosting_init(struct target *target)
+{
+	semihosting_common_init(target, riscv_semihosting_setup,
+		riscv_semihosting_post_result);
+}
+
+/**
+ * Check for and process a semihosting request using the ARM protocol). This
+ * is meant to be called when the target is stopped due to a debug mode entry.
+ * If the value 0 is returned then there was nothing to process. A non-zero
+ * return value signifies that a request was processed and the target resumed,
+ * or an error was encountered, in which case the caller must return
+ * immediately.
+ *
+ * @param target Pointer to the target to process.
+ * @param retval Pointer to a location where the return code will be stored
+ * @return non-zero value if a request was processed or an error encountered
+ */
+int riscv_semihosting(struct target *target, int *retval)
+{
+	struct semihosting *semihosting = target->semihosting;
+	if (!semihosting)
+		return 0;
+
+	if (!semihosting->is_active)
+		return 0;
+
+	riscv_reg_t dpc;
+	int result = riscv_get_register(target, &dpc, GDB_REGNO_DPC);
+	if (result != ERROR_OK)
+		return 0;
+
+	uint8_t tmp[12];
+
+	/* Read the current instruction, including the bracketing */
+	*retval = target_read_memory(target, dpc - 4, 2, 6, tmp);
+	if (*retval != ERROR_OK)
+		return 0;
+
+	/*
+	 * The instructions that trigger a semihosting call,
+	 * always uncompressed, should look like:
+	 *
+	 * 01f01013              slli    zero,zero,0x1f
+	 * 00100073              ebreak
+	 * 40705013              srai    zero,zero,0x7
+	 */
+	uint32_t pre = target_buffer_get_u32(target, tmp);
+	uint32_t ebreak = target_buffer_get_u32(target, tmp + 4);
+	uint32_t post = target_buffer_get_u32(target, tmp + 8);
+	LOG_DEBUG("check %08x %08x %08x from 0x%" PRIx64 "-4", pre, ebreak, post, dpc);
+
+	if (pre != 0x01f01013 || ebreak != 0x00100073 || post != 0x40705013) {
+
+		/* Not the magic sequence defining semihosting. */
+		return 0;
+	}
+
+	/*
+	 * Perform semihosting call if we are not waiting on a fileio
+	 * operation to complete.
+	 */
+	if (!semihosting->hit_fileio) {
+
+		/* RISC-V uses A0 and A1 to pass function arguments */
+		riscv_reg_t r0;
+		riscv_reg_t r1;
+
+		result = riscv_get_register(target, &r0, GDB_REGNO_A0);
+		if (result != ERROR_OK)
+			return 0;
+
+		result = riscv_get_register(target, &r1, GDB_REGNO_A1);
+		if (result != ERROR_OK)
+			return 0;
+
+		semihosting->op = r0;
+		semihosting->param = r1;
+		semihosting->word_size_bytes = riscv_xlen(target) / 8;
+
+		/* Check for ARM operation numbers. */
+		if (0 <= semihosting->op && semihosting->op <= 0x31) {
+			*retval = semihosting_common(target);
+			if (*retval != ERROR_OK) {
+				LOG_ERROR("Failed semihosting operation");
+				return 0;
+			}
+		} else {
+			/* Unknown operation number, not a semihosting call. */
+			return 0;
+		}
+	}
+
+	/*
+	 * Resume target if we are not waiting on a fileio
+	 * operation to complete.
+	 */
+	if (semihosting->is_resumable && !semihosting->hit_fileio) {
+		/* Resume right after the EBREAK 4 bytes instruction. */
+		*retval = target_resume(target, 0, dpc+4, 0, 0);
+		if (*retval != ERROR_OK) {
+			LOG_ERROR("Failed to resume target");
+			return 0;
+		}
+
+		return 1;
+	}
+
+	return 0;
+}
+
+/* -------------------------------------------------------------------------
+ * Local functions. */
+
+/**
+ * Called via semihosting->setup() later, after the target is known,
+ * usually on the first semihosting command.
+ */
+static int riscv_semihosting_setup(struct target *target, int enable)
+{
+	LOG_DEBUG("enable=%d", enable);
+
+	struct semihosting *semihosting = target->semihosting;
+	if (semihosting)
+		semihosting->setup_time = clock();
+
+	return ERROR_OK;
+}
+
+static int riscv_semihosting_post_result(struct target *target)
+{
+	struct semihosting *semihosting = target->semihosting;
+	if (!semihosting) {
+		/* If not enabled, silently ignored. */
+		return 0;
+	}
+
+	LOG_DEBUG("0x%" PRIx64, semihosting->result);
+	riscv_set_register(target, GDB_REGNO_A0, semihosting->result);
+	return 0;
+}