gdb_server: add support for architecture element

This change adds optional support for a target to report architecture
information in the target description to GDB. This is needed by some GDB
implementations to properly support remote target with custom behavior.
More information on the architecture element can be found here:

    https://sourceware.org/gdb/onlinedocs/gdb/Target-Description-Format.html#Target-Description-Format

Change-Id: I57b19cae5ac3496256e4e5cc52cf6526ca5c322d
Signed-off-by: Steven Stallion <stallion@squareup.com>
Reviewed-on: http://openocd.zylin.com/4078
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>

src/server/gdb_server.c

@@ -2196,6 +2196,7 @@ static int gdb_generate_target_description(struct target *target, char **tdesc_o
 	int retval = ERROR_OK;
 	struct reg **reg_list = NULL;
 	int reg_list_size;
+	char const *architecture;
 	char const **features = NULL;
 	char const **arch_defined_types = NULL;
 	int feature_list_size = 0;
@@ -2237,6 +2238,12 @@ static int gdb_generate_target_description(struct target *target, char **tdesc_o
 			"<!DOCTYPE target SYSTEM \"gdb-target.dtd\">\n"
 			"<target version=\"1.0\">\n");
 
+	/* generate architecture element if supported by target */
+	architecture = target_get_gdb_arch(target);
+	if (architecture != NULL)
+		xml_printf(&retval, &tdesc, &pos, &size,
+				"<architecture>%s</architecture>\n", architecture);
+
 	/* generate target description according to register list */
 	if (features != NULL) {
 		while (features[current_feature]) {
@@ -2386,6 +2393,8 @@ static int gdb_target_description_supported(struct target *target, int *supporte
 	char const **features = NULL;
 	int feature_list_size = 0;
 
+	char const *architecture = target_get_gdb_arch(target);
+
 	retval = target_get_gdb_reg_list(target, &reg_list,
 			&reg_list_size, REG_CLASS_ALL);
 	if (retval != ERROR_OK) {
@@ -2407,7 +2416,7 @@ static int gdb_target_description_supported(struct target *target, int *supporte
 	}
 
 	if (supported) {
-		if (feature_list_size)
+		if (architecture || feature_list_size)
 			*supported = 1;
 		else
 			*supported = 0;

src/target/target.c

@@ -1199,6 +1199,13 @@ int target_hit_watchpoint(struct target *target,
 	return target->type->hit_watchpoint(target, hit_watchpoint);
 }
 
+const char *target_get_gdb_arch(struct target *target)
+{
+	if (target->type->get_gdb_arch == NULL)
+		return NULL;
+	return target->type->get_gdb_arch(target);
+}
+
 int target_get_gdb_reg_list(struct target *target,
 		struct reg **reg_list[], int *reg_list_size,
 		enum target_register_class reg_class)

src/target/target.h

@@ -472,6 +472,13 @@ int target_remove_watchpoint(struct target *target,
 int target_hit_watchpoint(struct target *target,
 		struct watchpoint **watchpoint);
 
+/**
+ * Obtain the architecture for GDB.
+ *
+ * This routine is a wrapper for target->type->get_gdb_arch.
+ */
+const char *target_get_gdb_arch(struct target *target);
+
 /**
  * Obtain the registers for GDB.
  *

src/target/target_type.h

@@ -88,6 +88,15 @@ struct target_type {
 	int (*deassert_reset)(struct target *target);
 	int (*soft_reset_halt)(struct target *target);
 
+	/**
+	 * Target architecture for GDB.
+	 *
+	 * The string returned by this function will not be automatically freed;
+	 * if dynamic allocation is used for this value, it must be managed by
+	 * the target, ideally by caching the result for subsequent calls.
+	 */
+	const char *(*get_gdb_arch)(struct target *target);
+
 	/**
 	 * Target register access for GDB.  Do @b not call this function
 	 * directly, use target_get_gdb_reg_list() instead.