semihosting: support fileio operation

This patch adds support for bridging semihosting to GDB's File-I/O
remote protocol extension. For the most part operations match up 1:1,
however some require a working area to complete successfully, namely
operations that devolve to read, stat, and gettimeofday.

A new command was added to enable support for fileio named `arm
semihosting_fileio`, which ensures that the default behavior remains
intact for those that prefer it.

Finally, redundant logging was removed from the target_arch_state
function; this permits ARM targets to quiesce log output when polling
for a fileio reply. This prevents filling the logs with halt/resume
messages when using semihosting fileio.

Change-Id: Ifbb864fc2373336a501cc0332675b887b552e1ee
Signed-off-by: Steven Stallion <stallion@squareup.com>
Reviewed-on: http://openocd.zylin.com/3566
Tested-by: jenkins
Reviewed-by: Steven Stallion <sstallion@gmail.com>
Reviewed-by: Paul Fertser <fercerpav@gmail.com>

12 files changed, 448 insertions, 158 deletions

diff --git a/doc/openocd.texi b/doc/openocd.texi
index 372683a..1cca4ab 100644
--- a/doc/openocd.texi
+++ b/doc/openocd.texi
@@ -7404,6 +7404,17 @@ requests by using a special SVC instruction that is trapped at the
 Supervisor Call vector by OpenOCD.
 @end deffn
 
+@deffn Command {arm semihosting_fileio} [@option{enable}|@option{disable}]
+@cindex ARM semihosting
+Display status of semihosting fileio, after optionally changing that
+status.
+
+Enabling this option forwards semihosting I/O to GDB process using the
+File-I/O remote protocol extension. This is especially useful for
+interacting with remote files or displaying console messages in the
+debugger.
+@end deffn
+
 @section ARMv4 and ARMv5 Architecture
 @cindex ARMv4
 @cindex ARMv5
diff --git a/src/target/arm.h b/src/target/arm.h
index 28022e3..226dd65 100644
--- a/src/target/arm.h
+++ b/src/target/arm.h
@@ -130,6 +130,18 @@ struct arm {
 	/** Flag reporting whether semihosting is active. */
 	bool is_semihosting;
 
+	/** Flag reporting whether semihosting fileio is active. */
+	bool is_semihosting_fileio;
+
+	/** Flag reporting whether semihosting fileio operation is active. */
+	bool semihosting_hit_fileio;
+
+	/** Current semihosting operation. */
+	int semihosting_op;
+
+	/** Current semihosting result. */
+	int semihosting_result;
+
 	/** Value to be returned by semihosting SYS_ERRNO request. */
 	int semihosting_errno;
 
diff --git a/src/target/arm7tdmi.c b/src/target/arm7tdmi.c
index 58ab027..9dcb302 100644
--- a/src/target/arm7tdmi.c
+++ b/src/target/arm7tdmi.c
@@ -30,6 +30,7 @@
 #include "target_type.h"
 #include "register.h"
 #include "arm_opcodes.h"
+#include "arm_semihosting.h"
 
 /*
  * For information about ARM7TDMI, see ARM DDI 0210C (r4p1)
@@ -615,7 +616,7 @@ static void arm7tdmi_build_reg_cache(struct target *target)
 int arm7tdmi_init_target(struct command_context *cmd_ctx, struct target *target)
 {
 	arm7tdmi_build_reg_cache(target);
-
+	arm_semihosting_init(target);
 	return ERROR_OK;
 }
 
diff --git a/src/target/arm9tdmi.c b/src/target/arm9tdmi.c
index eed965a..82b430f 100644
--- a/src/target/arm9tdmi.c
+++ b/src/target/arm9tdmi.c
@@ -30,6 +30,7 @@
 #include "target_type.h"
 #include "register.h"
 #include "arm_opcodes.h"
+#include "arm_semihosting.h"
 
 /*
  * NOTE:  this holds code that's used with multiple ARM9 processors:
@@ -714,6 +715,7 @@ int arm9tdmi_init_target(struct command_context *cmd_ctx,
 		struct target *target)
 {
 	arm9tdmi_build_reg_cache(target);
+	arm_semihosting_init(target);
 	return ERROR_OK;
 }
 
diff --git a/src/target/arm_semihosting.c b/src/target/arm_semihosting.c
index 63335ff..2525119 100644
--- a/src/target/arm_semihosting.c
+++ b/src/target/arm_semihosting.c
@@ -5,6 +5,9 @@
  *   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     *
@@ -43,6 +46,7 @@
 #include "cortex_m.h"
 #include "register.h"
 #include "arm_opcodes.h"
+#include "target_type.h"
 #include "arm_semihosting.h"
 #include <helper/binarybuffer.h>
 #include <helper/log.h>
@@ -63,13 +67,59 @@ static const int open_modeflags[12] = {
 	O_RDWR | O_CREAT | O_APPEND | O_BINARY
 };
 
+static int post_result(struct target *target)
+{
+	struct arm *arm = target_to_arm(target);
+
+	/* REVISIT this looks wrong ... ARM11 and Cortex-A8
+	 * should work this way at least sometimes.
+	 */
+	if (is_arm7_9(target_to_arm7_9(target)) ||
+	    is_armv7a(target_to_armv7a(target))) {
+		uint32_t spsr;
+
+		/* return value in R0 */
+		buf_set_u32(arm->core_cache->reg_list[0].value, 0, 32, arm->semihosting_result);
+		arm->core_cache->reg_list[0].dirty = 1;
+
+		/* LR --> PC */
+		buf_set_u32(arm->core_cache->reg_list[15].value, 0, 32,
+			buf_get_u32(arm_reg_current(arm, 14)->value, 0, 32));
+		arm->core_cache->reg_list[15].dirty = 1;
+
+		/* saved PSR --> current PSR */
+		spsr = buf_get_u32(arm->spsr->value, 0, 32);
+
+		/* REVISIT should this be arm_set_cpsr(arm, spsr)
+		 * instead of a partially unrolled version?
+		 */
+
+		buf_set_u32(arm->cpsr->value, 0, 32, spsr);
+		arm->cpsr->dirty = 1;
+		arm->core_mode = spsr & 0x1f;
+		if (spsr & 0x20)
+			arm->core_state = ARM_STATE_THUMB;
+
+	} else {
+		/* resume execution, this will be pc+2 to skip over the
+		 * bkpt instruction */
+
+		/* return result in R0 */
+		buf_set_u32(arm->core_cache->reg_list[0].value, 0, 32, arm->semihosting_result);
+		arm->core_cache->reg_list[0].dirty = 1;
+	}
+
+	return ERROR_OK;
+}
+
 static int do_semihosting(struct target *target)
 {
 	struct arm *arm = target_to_arm(target);
+	struct gdb_fileio_info *fileio_info = target->fileio_info;
 	uint32_t r0 = buf_get_u32(arm->core_cache->reg_list[0].value, 0, 32);
 	uint32_t r1 = buf_get_u32(arm->core_cache->reg_list[1].value, 0, 32);
 	uint8_t params[16];
-	int retval, result;
+	int retval;
 
 	/*
 	 * TODO: lots of security issues are not considered yet, such as:
@@ -77,10 +127,10 @@ static int do_semihosting(struct target *target)
 	 * - no safety checks on opened/deleted/renamed file paths
 	 * Beware the target app you use this support with.
 	 *
-	 * TODO: explore mapping requests to GDB's "File-I/O Remote
-	 * Protocol Extension" ... when GDB is active.
+	 * TODO: unsupported semihosting fileio operations could be
+	 * implemented if we had a small working area at our disposal.
 	 */
-	switch (r0) {
+	switch ((arm->semihosting_op = r0)) {
 	case 0x01:	/* SYS_OPEN */
 		retval = target_read_memory(target, r1, 4, 3, params);
 		if (retval != ERROR_OK)
@@ -89,27 +139,40 @@ static int do_semihosting(struct target *target)
 			uint32_t a = target_buffer_get_u32(target, params+0);
 			uint32_t m = target_buffer_get_u32(target, params+4);
 			uint32_t l = target_buffer_get_u32(target, params+8);
-			if (l <= 255 && m <= 11) {
-				uint8_t fn[256];
-				retval = target_read_memory(target, a, 1, l, fn);
-				if (retval != ERROR_OK)
-					return retval;
-				fn[l] = 0;
-				if (strcmp((char *)fn, ":tt") == 0) {
-					if (m < 4)
-						result = dup(STDIN_FILENO);
-					else
-						result = dup(STDOUT_FILENO);
-				} else {
-					/* cygwin requires the permission setting
-					 * otherwise it will fail to reopen a previously
-					 * written file */
-					result = open((char *)fn, open_modeflags[m], 0644);
+			uint8_t fn[256];
+			retval = target_read_memory(target, a, 1, l, fn);
+			if (retval != ERROR_OK)
+				return retval;
+			fn[l] = 0;
+			if (arm->is_semihosting_fileio) {
+				if (strcmp((char *)fn, ":tt") == 0)
+					arm->semihosting_result = 0;
+				else {
+					arm->semihosting_hit_fileio = true;
+					fileio_info->identifier = "open";
+					fileio_info->param_1 = a;
+					fileio_info->param_2 = l;
+					fileio_info->param_3 = open_modeflags[m];
+					fileio_info->param_4 = 0644;
 				}
-				arm->semihosting_errno =  errno;
 			} else {
-				result = -1;
-				arm->semihosting_errno = EINVAL;
+				if (l <= 255 && m <= 11) {
+					if (strcmp((char *)fn, ":tt") == 0) {
+						if (m < 4)
+							arm->semihosting_result = dup(STDIN_FILENO);
+						else
+							arm->semihosting_result = dup(STDOUT_FILENO);
+					} else {
+						/* cygwin requires the permission setting
+						 * otherwise it will fail to reopen a previously
+						 * written file */
+						arm->semihosting_result = open((char *)fn, open_modeflags[m], 0644);
+					}
+					arm->semihosting_errno =  errno;
+				} else {
+					arm->semihosting_result = -1;
+					arm->semihosting_errno = EINVAL;
+				}
 			}
 		}
 		break;
@@ -120,33 +183,63 @@ static int do_semihosting(struct target *target)
 			return retval;
 		else {
 			int fd = target_buffer_get_u32(target, params+0);
-			result = close(fd);
-			arm->semihosting_errno = errno;
+			if (arm->is_semihosting_fileio) {
+				arm->semihosting_hit_fileio = true;
+				fileio_info->identifier = "close";
+				fileio_info->param_1 = fd;
+			} else {
+				arm->semihosting_result = close(fd);
+				arm->semihosting_errno = errno;
+			}
 		}
 		break;
 
 	case 0x03:	/* SYS_WRITEC */
-		{
+		if (arm->is_semihosting_fileio) {
+			arm->semihosting_hit_fileio = true;
+			fileio_info->identifier = "write";
+			fileio_info->param_1 = 1;
+			fileio_info->param_2 = r1;
+			fileio_info->param_3 = 1;
+		} else {
 			unsigned char c;
 			retval = target_read_memory(target, r1, 1, 1, &c);
 			if (retval != ERROR_OK)
 				return retval;
 			putchar(c);
-			result = 0;
+			arm->semihosting_result = 0;
 		}
 		break;
 
 	case 0x04:	/* SYS_WRITE0 */
-		do {
-			unsigned char c;
-			retval = target_read_memory(target, r1++, 1, 1, &c);
-			if (retval != ERROR_OK)
-				return retval;
-			if (!c)
-				break;
-			putchar(c);
-		} while (1);
-		result = 0;
+		if (arm->is_semihosting_fileio) {
+			size_t count = 0;
+			for (uint32_t a = r1;; a++) {
+				unsigned char c;
+				retval = target_read_memory(target, a, 1, 1, &c);
+				if (retval != ERROR_OK)
+					return retval;
+				if (c == '\0')
+					break;
+				count++;
+			}
+			arm->semihosting_hit_fileio = true;
+			fileio_info->identifier = "write";
+			fileio_info->param_1 = 1;
+			fileio_info->param_2 = r1;
+			fileio_info->param_3 = count;
+		} else {
+			do {
+				unsigned char c;
+				retval = target_read_memory(target, r1++, 1, 1, &c);
+				if (retval != ERROR_OK)
+					return retval;
+				if (!c)
+					break;
+				putchar(c);
+			} while (1);
+			arm->semihosting_result = 0;
+		}
 		break;
 
 	case 0x05:	/* SYS_WRITE */
@@ -157,21 +250,29 @@ static int do_semihosting(struct target *target)
 			int fd = target_buffer_get_u32(target, params+0);
 			uint32_t a = target_buffer_get_u32(target, params+4);
 			size_t l = target_buffer_get_u32(target, params+8);
-			uint8_t *buf = malloc(l);
-			if (!buf) {
-				result = -1;
-				arm->semihosting_errno = ENOMEM;
+			if (arm->is_semihosting_fileio) {
+				arm->semihosting_hit_fileio = true;
+				fileio_info->identifier = "write";
+				fileio_info->param_1 = fd;
+				fileio_info->param_2 = a;
+				fileio_info->param_3 = l;
 			} else {
-				retval = target_read_buffer(target, a, l, buf);
-				if (retval != ERROR_OK) {
+				uint8_t *buf = malloc(l);
+				if (!buf) {
+					arm->semihosting_result = -1;
+					arm->semihosting_errno = ENOMEM;
+				} else {
+					retval = target_read_buffer(target, a, l, buf);
+					if (retval != ERROR_OK) {
+						free(buf);
+						return retval;
+					}
+					arm->semihosting_result = write(fd, buf, l);
+					arm->semihosting_errno = errno;
+					if (arm->semihosting_result >= 0)
+						arm->semihosting_result = l - arm->semihosting_result;
 					free(buf);
-					return retval;
 				}
-				result = write(fd, buf, l);
-				arm->semihosting_errno = errno;
-				if (result >= 0)
-					result = l - result;
-				free(buf);
 			}
 		}
 		break;
@@ -184,42 +285,60 @@ static int do_semihosting(struct target *target)
 			int fd = target_buffer_get_u32(target, params+0);
 			uint32_t a = target_buffer_get_u32(target, params+4);
 			ssize_t l = target_buffer_get_u32(target, params+8);
-			uint8_t *buf = malloc(l);
-			if (!buf) {
-				result = -1;
-				arm->semihosting_errno = ENOMEM;
+			if (arm->is_semihosting_fileio) {
+				arm->semihosting_hit_fileio = true;
+				fileio_info->identifier = "read";
+				fileio_info->param_1 = fd;
+				fileio_info->param_2 = a;
+				fileio_info->param_3 = l;
 			} else {
-				result = read(fd, buf, l);
-				arm->semihosting_errno = errno;
-				if (result >= 0) {
-					retval = target_write_buffer(target, a, result, buf);
-					if (retval != ERROR_OK) {
-						free(buf);
-						return retval;
+				uint8_t *buf = malloc(l);
+				if (!buf) {
+					arm->semihosting_result = -1;
+					arm->semihosting_errno = ENOMEM;
+				} else {
+					arm->semihosting_result = read(fd, buf, l);
+					arm->semihosting_errno = errno;
+					if (arm->semihosting_result >= 0) {
+						retval = target_write_buffer(target, a, arm->semihosting_result, buf);
+						if (retval != ERROR_OK) {
+							free(buf);
+							return retval;
+						}
+						arm->semihosting_result = l - arm->semihosting_result;
 					}
-					result = l - result;
+					free(buf);
 				}
-				free(buf);
 			}
 		}
 		break;
 
 	case 0x07:	/* SYS_READC */
-		result = getchar();
+		if (arm->is_semihosting_fileio) {
+			LOG_ERROR("SYS_READC not supported by semihosting fileio");
+			return ERROR_FAIL;
+		}
+		arm->semihosting_result = getchar();
 		break;
 
 	case 0x08:	/* SYS_ISERROR */
 		retval = target_read_memory(target, r1, 4, 1, params);
 		if (retval != ERROR_OK)
 			return retval;
-		result = (target_buffer_get_u32(target, params+0) != 0);
+		arm->semihosting_result = (target_buffer_get_u32(target, params+0) != 0);
 		break;
 
 	case 0x09:	/* SYS_ISTTY */
-		retval = target_read_memory(target, r1, 4, 1, params);
-		if (retval != ERROR_OK)
-			return retval;
-		result = isatty(target_buffer_get_u32(target, params+0));
+		if (arm->is_semihosting_fileio) {
+			arm->semihosting_hit_fileio = true;
+			fileio_info->identifier = "isatty";
+			fileio_info->param_1 = r1;
+		} else {
+			retval = target_read_memory(target, r1, 4, 1, params);
+			if (retval != ERROR_OK)
+				return retval;
+			arm->semihosting_result = isatty(target_buffer_get_u32(target, params+0));
+		}
 		break;
 
 	case 0x0a:	/* SYS_SEEK */
@@ -229,27 +348,39 @@ static int do_semihosting(struct target *target)
 		else {
 			int fd = target_buffer_get_u32(target, params+0);
 			off_t pos = target_buffer_get_u32(target, params+4);
-			result = lseek(fd, pos, SEEK_SET);
-			arm->semihosting_errno = errno;
-			if (result == pos)
-				result = 0;
+			if (arm->is_semihosting_fileio) {
+				arm->semihosting_hit_fileio = true;
+				fileio_info->identifier = "lseek";
+				fileio_info->param_1 = fd;
+				fileio_info->param_2 = pos;
+				fileio_info->param_3 = SEEK_SET;
+			} else {
+				arm->semihosting_result = lseek(fd, pos, SEEK_SET);
+				arm->semihosting_errno = errno;
+				if (arm->semihosting_result == pos)
+					arm->semihosting_result = 0;
+			}
 		}
 		break;
 
 	case 0x0c:	/* SYS_FLEN */
+		if (arm->is_semihosting_fileio) {
+			LOG_ERROR("SYS_FLEN not supported by semihosting fileio");
+			return ERROR_FAIL;
+		}
 		retval = target_read_memory(target, r1, 4, 1, params);
 		if (retval != ERROR_OK)
 			return retval;
 		else {
 			int fd = target_buffer_get_u32(target, params+0);
 			struct stat buf;
-			result = fstat(fd, &buf);
-			if (result == -1) {
+			arm->semihosting_result = fstat(fd, &buf);
+			if (arm->semihosting_result == -1) {
 				arm->semihosting_errno = errno;
-				result = -1;
+				arm->semihosting_result = -1;
 				break;
 			}
-			result = buf.st_size;
+			arm->semihosting_result = buf.st_size;
 		}
 		break;
 
@@ -260,17 +391,24 @@ static int do_semihosting(struct target *target)
 		else {
 			uint32_t a = target_buffer_get_u32(target, params+0);
 			uint32_t l = target_buffer_get_u32(target, params+4);
-			if (l <= 255) {
-				uint8_t fn[256];
-				retval = target_read_memory(target, a, 1, l, fn);
-				if (retval != ERROR_OK)
-					return retval;
-				fn[l] = 0;
-				result = remove((char *)fn);
-				arm->semihosting_errno =  errno;
+			if (arm->is_semihosting_fileio) {
+				arm->semihosting_hit_fileio = true;
+				fileio_info->identifier = "unlink";
+				fileio_info->param_1 = a;
+				fileio_info->param_2 = l;
 			} else {
-				result = -1;
-				arm->semihosting_errno = EINVAL;
+				if (l <= 255) {
+					uint8_t fn[256];
+					retval = target_read_memory(target, a, 1, l, fn);
+					if (retval != ERROR_OK)
+						return retval;
+					fn[l] = 0;
+					arm->semihosting_result = remove((char *)fn);
+					arm->semihosting_errno =  errno;
+				} else {
+					arm->semihosting_result = -1;
+					arm->semihosting_errno = EINVAL;
+				}
 			}
 		}
 		break;
@@ -284,31 +422,40 @@ static int do_semihosting(struct target *target)
 			uint32_t l1 = target_buffer_get_u32(target, params+4);
 			uint32_t a2 = target_buffer_get_u32(target, params+8);
 			uint32_t l2 = target_buffer_get_u32(target, params+12);
-			if (l1 <= 255 && l2 <= 255) {
-				uint8_t fn1[256], fn2[256];
-				retval = target_read_memory(target, a1, 1, l1, fn1);
-				if (retval != ERROR_OK)
-					return retval;
-				retval = target_read_memory(target, a2, 1, l2, fn2);
-				if (retval != ERROR_OK)
-					return retval;
-				fn1[l1] = 0;
-				fn2[l2] = 0;
-				result = rename((char *)fn1, (char *)fn2);
-				arm->semihosting_errno =  errno;
+			if (arm->is_semihosting_fileio) {
+				arm->semihosting_hit_fileio = true;
+				fileio_info->identifier = "rename";
+				fileio_info->param_1 = a1;
+				fileio_info->param_2 = l1;
+				fileio_info->param_3 = a2;
+				fileio_info->param_4 = l2;
 			} else {
-				result = -1;
-				arm->semihosting_errno = EINVAL;
+				if (l1 <= 255 && l2 <= 255) {
+					uint8_t fn1[256], fn2[256];
+					retval = target_read_memory(target, a1, 1, l1, fn1);
+					if (retval != ERROR_OK)
+						return retval;
+					retval = target_read_memory(target, a2, 1, l2, fn2);
+					if (retval != ERROR_OK)
+						return retval;
+					fn1[l1] = 0;
+					fn2[l2] = 0;
+					arm->semihosting_result = rename((char *)fn1, (char *)fn2);
+					arm->semihosting_errno =  errno;
+				} else {
+					arm->semihosting_result = -1;
+					arm->semihosting_errno = EINVAL;
+				}
 			}
 		}
 		break;
 
 	case 0x11:	/* SYS_TIME */
-		result = time(NULL);
+		arm->semihosting_result = time(NULL);
 		break;
 
 	case 0x13:	/* SYS_ERRNO */
-		result = arm->semihosting_errno;
+		arm->semihosting_result = arm->semihosting_errno;
 		break;
 
 	case 0x15:	/* SYS_GET_CMDLINE */
@@ -321,12 +468,12 @@ static int do_semihosting(struct target *target)
 			char *arg = "foobar";
 			uint32_t s = strlen(arg) + 1;
 			if (l < s)
-				result = -1;
+				arm->semihosting_result = -1;
 			else {
 				retval = target_write_buffer(target, a, s, (uint8_t *)arg);
 				if (retval != ERROR_OK)
 					return retval;
-				result = 0;
+				arm->semihosting_result = 0;
 			}
 		}
 		break;
@@ -342,7 +489,7 @@ static int do_semihosting(struct target *target)
 			retval = target_write_memory(target, a, 4, 4, params);
 			if (retval != ERROR_OK)
 				return retval;
-			result = 0;
+			arm->semihosting_result = 0;
 		}
 		break;
 
@@ -386,17 +533,24 @@ static int do_semihosting(struct target *target)
 		else {
 			uint32_t len = target_buffer_get_u32(target, params+4);
 			uint32_t c_ptr = target_buffer_get_u32(target, params);
-			uint8_t cmd[256];
-			if (len > 255) {
-				result = -1;
-				arm->semihosting_errno = EINVAL;
+			if (arm->is_semihosting_fileio) {
+				arm->semihosting_hit_fileio = true;
+				fileio_info->identifier = "system";
+				fileio_info->param_1 = c_ptr;
+				fileio_info->param_2 = len;
 			} else {
-				memset(cmd, 0x0, 256);
-				retval = target_read_memory(target, c_ptr, 1, len, cmd);
-				if (retval != ERROR_OK)
-					return retval;
-				else
-					result = system((const char *)cmd);
+				uint8_t cmd[256];
+				if (len > 255) {
+					arm->semihosting_result = -1;
+					arm->semihosting_errno = EINVAL;
+				} else {
+					memset(cmd, 0x0, 256);
+					retval = target_read_memory(target, c_ptr, 1, len, cmd);
+					if (retval != ERROR_OK)
+						return retval;
+					else
+						arm->semihosting_result = system((const char *)cmd);
+				}
 			}
 		}
 		break;
@@ -408,51 +562,84 @@ static int do_semihosting(struct target *target)
 	default:
 		fprintf(stderr, "semihosting: unsupported call %#x\n",
 				(unsigned) r0);
-		result = -1;
+		arm->semihosting_result = -1;
 		arm->semihosting_errno = ENOTSUP;
 	}
 
-	/* resume execution to the original mode */
+	return ERROR_OK;
+}
 
-	/* REVISIT this looks wrong ... ARM11 and Cortex-A8
-	 * should work this way at least sometimes.
+static int get_gdb_fileio_info(struct target *target, struct gdb_fileio_info *fileio_info)
+{
+	struct arm *arm = target_to_arm(target);
+
+	/* To avoid uneccessary duplication, semihosting prepares the
+	 * fileio_info structure out-of-band when the target halts. See
+	 * do_semihosting for more detail.
 	 */
-	if (is_arm7_9(target_to_arm7_9(target)) ||
-	    is_armv7a(target_to_armv7a(target))) {
-		uint32_t spsr;
+	if (!arm->is_semihosting_fileio || !arm->semihosting_hit_fileio)
+		return ERROR_FAIL;
 
-		/* return value in R0 */
-		buf_set_u32(arm->core_cache->reg_list[0].value, 0, 32, result);
-		arm->core_cache->reg_list[0].dirty = 1;
+	return ERROR_OK;
+}
 
-		/* LR --> PC */
-		buf_set_u32(arm->core_cache->reg_list[15].value, 0, 32,
-			buf_get_u32(arm_reg_current(arm, 14)->value, 0, 32));
-		arm->core_cache->reg_list[15].dirty = 1;
+static int gdb_fileio_end(struct target *target, int result, int fileio_errno, bool ctrl_c)
+{
+	struct arm *arm = target_to_arm(target);
+	struct gdb_fileio_info *fileio_info = target->fileio_info;
 
-		/* saved PSR --> current PSR */
-		spsr = buf_get_u32(arm->spsr->value, 0, 32);
+	/* clear pending status */
+	arm->semihosting_hit_fileio = false;
 
-		/* REVISIT should this be arm_set_cpsr(arm, spsr)
-		 * instead of a partially unrolled version?
-		 */
+	arm->semihosting_result = result;
+	arm->semihosting_errno = fileio_errno;
 
-		buf_set_u32(arm->cpsr->value, 0, 32, spsr);
-		arm->cpsr->dirty = 1;
-		arm->core_mode = spsr & 0x1f;
-		if (spsr & 0x20)
-			arm->core_state = ARM_STATE_THUMB;
+	/* Some fileio results do not match up with what the semihosting
+	 * operation expects; for these operations, we munge the results
+	 * below:
+	 */
+	switch (arm->semihosting_op) {
+	case 0x05:	/* SYS_WRITE */
+		if (result < 0)
+			arm->semihosting_result = fileio_info->param_3;
+		else
+			arm->semihosting_result = 0;
+		break;
 
-	} else {
-		/* resume execution, this will be pc+2 to skip over the
-		 * bkpt instruction */
+	case 0x06:	/* SYS_READ */
+		if (result == (int)fileio_info->param_3)
+			arm->semihosting_result = 0;
+		if (result <= 0)
+			arm->semihosting_result = fileio_info->param_3;
+		break;
 
-		/* return result in R0 */
-		buf_set_u32(arm->core_cache->reg_list[0].value, 0, 32, result);
-		arm->core_cache->reg_list[0].dirty = 1;
+	case 0x0a:	/* SYS_SEEK */
+		if (result > 0)
+			arm->semihosting_result = 0;
+		break;
 	}
 
-	return target_resume(target, 1, 0, 0, 0);
+	return post_result(target);
+}
+
+/**
+ * Initialize ARM semihosting support.
+ *
+ * @param target Pointer to the ARM target to initialize.
+ * @return An error status if there is a problem during initialization.
+ */
+int arm_semihosting_init(struct target *target)
+{
+	target->fileio_info = malloc(sizeof(*target->fileio_info));
+	if (target->fileio_info == NULL) {
+		LOG_ERROR("out of memory");
+		return ERROR_FAIL;
+	}
+
+	target->type->get_gdb_fileio_info = get_gdb_fileio_info;
+	target->type->gdb_fileio_end = gdb_fileio_end;
+
+	return ERROR_OK;
 }
 
 /**
@@ -576,6 +763,35 @@ int arm_semihosting(struct target *target, int *retval)
 		return 0;
 	}
 
-	*retval = do_semihosting(target);
-	return 1;
+	/* Perform semihosting if we are not waiting on a fileio
+	 * operation to complete.
+	 */
+	if (!arm->semihosting_hit_fileio) {
+		*retval = do_semihosting(target);
+		if (*retval != ERROR_OK) {
+			LOG_ERROR("Failed semihosting operation");
+			return 0;
+		}
+	}
+
+	/* Post result to target if we are not waiting on a fileio
+	 * operation to complete:
+	 */
+	if (!arm->semihosting_hit_fileio) {
+		*retval = post_result(target);
+		if (*retval != ERROR_OK) {
+			LOG_ERROR("Failed to post semihosting result");
+			return 0;
+		}
+
+		*retval = target_resume(target, 1, 0, 0, 0);
+		if (*retval != ERROR_OK) {
+			LOG_ERROR("Failed to resume target");
+			return 0;
+		}
+
+		return 1;
+	}
+
+	return 0;
 }
diff --git a/src/target/arm_semihosting.h b/src/target/arm_semihosting.h
index 7b5c0b2..011f19f 100644
--- a/src/target/arm_semihosting.h
+++ b/src/target/arm_semihosting.h
@@ -19,6 +19,7 @@
 #ifndef OPENOCD_TARGET_ARM_SEMIHOSTING_H
 #define OPENOCD_TARGET_ARM_SEMIHOSTING_H
 
+int arm_semihosting_init(struct target *target);
 int arm_semihosting(struct target *target, int *retval);
 
 #endif /* OPENOCD_TARGET_ARM_SEMIHOSTING_H */
diff --git a/src/target/armv4_5.c b/src/target/armv4_5.c
index 1a31d40..624a254 100644
--- a/src/target/armv4_5.c
+++ b/src/target/armv4_5.c
@@ -666,14 +666,19 @@ int arm_arch_state(struct target *target)
 		return ERROR_FAIL;
 	}
 
+	/* avoid filling log waiting for fileio reply */
+	if (arm->semihosting_hit_fileio)
+		return ERROR_OK;
+
 	LOG_USER("target halted in %s state due to %s, current mode: %s\n"
-		"cpsr: 0x%8.8" PRIx32 " pc: 0x%8.8" PRIx32 "%s",
+		"cpsr: 0x%8.8" PRIx32 " pc: 0x%8.8" PRIx32 "%s%s",
 		arm_state_strings[arm->core_state],
 		debug_reason_name(target),
 		arm_mode_name(arm->core_mode),
 		buf_get_u32(arm->cpsr->value, 0, 32),
 		buf_get_u32(arm->pc->value, 0, 32),
-		arm->is_semihosting ? ", semihosting" : "");
+		arm->is_semihosting ? ", semihosting" : "",
+		arm->is_semihosting_fileio ? " fileio" : "");
 
 	return ERROR_OK;
 }
@@ -1055,6 +1060,37 @@ COMMAND_HANDLER(handle_arm_semihosting_command)
 	return ERROR_OK;
 }
 
+COMMAND_HANDLER(handle_arm_semihosting_fileio_command)
+{
+	struct target *target = get_current_target(CMD_CTX);
+
+	if (target == NULL) {
+		LOG_ERROR("No target selected");
+		return ERROR_FAIL;
+	}
+
+	struct arm *arm = target_to_arm(target);
+
+	if (!is_arm(arm)) {
+		command_print(CMD_CTX, "current target isn't an ARM");
+		return ERROR_FAIL;
+	}
+
+	if (!arm->is_semihosting) {
+		command_print(CMD_CTX, "semihosting is not enabled");
+		return ERROR_FAIL;
+	}
+
+	if (CMD_ARGC > 0)
+		COMMAND_PARSE_ENABLE(CMD_ARGV[0], arm->is_semihosting_fileio);
+
+	command_print(CMD_CTX, "semihosting fileio is %s",
+		arm->is_semihosting_fileio
+		? "enabled" : "disabled");
+
+	return ERROR_OK;
+}
+
 static const struct command_registration arm_exec_command_handlers[] = {
 	{
 		.name = "reg",
@@ -1097,6 +1133,13 @@ static const struct command_registration arm_exec_command_handlers[] = {
 		.usage = "['enable'|'disable']",
 		.help = "activate support for semihosting operations",
 	},
+	{
+		"semihosting_fileio",
+		.handler = handle_arm_semihosting_fileio_command,
+		.mode = COMMAND_EXEC,
+		.usage = "['enable'|'disable']",
+		.help = "activate support for semihosting fileio operations",
+	},
 
 	COMMAND_REGISTRATION_DONE
 };
diff --git a/src/target/armv7m.c b/src/target/armv7m.c
index 60b244a..64d18d7 100644
--- a/src/target/armv7m.c
+++ b/src/target/armv7m.c
@@ -536,11 +536,15 @@ int armv7m_arch_state(struct target *target)
 	struct arm *arm = &armv7m->arm;
 	uint32_t ctrl, sp;
 
+	/* avoid filling log waiting for fileio reply */
+	if (arm->semihosting_hit_fileio)
+		return ERROR_OK;
+
 	ctrl = buf_get_u32(arm->core_cache->reg_list[ARMV7M_CONTROL].value, 0, 32);
 	sp = buf_get_u32(arm->core_cache->reg_list[ARMV7M_R13].value, 0, 32);
 
 	LOG_USER("target halted due to %s, current mode: %s %s\n"
-		"xPSR: %#8.8" PRIx32 " pc: %#8.8" PRIx32 " %csp: %#8.8" PRIx32 "%s",
+		"xPSR: %#8.8" PRIx32 " pc: %#8.8" PRIx32 " %csp: %#8.8" PRIx32 "%s%s",
 		debug_reason_name(target),
 		arm_mode_name(arm->core_mode),
 		armv7m_exception_string(armv7m->exception_number),
@@ -548,7 +552,8 @@ int armv7m_arch_state(struct target *target)
 		buf_get_u32(arm->pc->value, 0, 32),
 		(ctrl & 0x02) ? 'p' : 'm',
 		sp,
-		arm->is_semihosting ? ", semihosting" : "");
+		arm->is_semihosting ? ", semihosting" : "",
+		arm->is_semihosting_fileio ? " fileio" : "");
 
 	return ERROR_OK;
 }
diff --git a/src/target/cortex_a.c b/src/target/cortex_a.c
index 91fa48e..ed2f613 100644
--- a/src/target/cortex_a.c
+++ b/src/target/cortex_a.c
@@ -3103,6 +3103,7 @@ static int cortex_a_init_target(struct command_context *cmd_ctx,
 	struct target *target)
 {
 	/* examine_first() does a bunch of this */
+	arm_semihosting_init(target);
 	return ERROR_OK;
 }
 
diff --git a/src/target/cortex_m.c b/src/target/cortex_m.c
index 4270f8f..f674cc5 100644
--- a/src/target/cortex_m.c
+++ b/src/target/cortex_m.c
@@ -1696,6 +1696,7 @@ static int cortex_m_init_target(struct command_context *cmd_ctx,
 	struct target *target)
 {
 	armv7m_build_reg_cache(target);
+	arm_semihosting_init(target);
 	return ERROR_OK;
 }
 
diff --git a/src/target/hla_target.c b/src/target/hla_target.c
index e02abc4..feeb11f 100644
--- a/src/target/hla_target.c
+++ b/src/target/hla_target.c
@@ -341,7 +341,7 @@ static int adapter_init_target(struct command_context *cmd_ctx,
 	LOG_DEBUG("%s", __func__);
 
 	armv7m_build_reg_cache(target);
-
+	arm_semihosting_init(target);
 	return ERROR_OK;
 }
 
diff --git a/src/target/target.c b/src/target/target.c
index 26bae4b..17902a5 100644
--- a/src/target/target.c
+++ b/src/target/target.c
@@ -1944,13 +1944,10 @@ int target_arch_state(struct target *target)
 {
 	int retval;
 	if (target == NULL) {
-		LOG_USER("No target has been configured");
+		LOG_WARNING("No target has been configured");
 		return ERROR_OK;
 	}
 
-	LOG_USER("%s: target state: %s", target_name(target),
-		 target_state_name(target));
-
 	if (target->state != TARGET_HALTED)
 		return ERROR_OK;