From 07e007e1ca0e72bea91f68ae639fd5266cf7c388 Mon Sep 17 00:00:00 2001
From: John Baldwin <jhb@FreeBSD.org>
Date: Fri, 24 May 2019 22:11:37 +0000
Subject: [PATCH] Add initial support for 'qSupported' to the debug server.

This doesn't recognize any features yet, but does parse the features
string.  It advertises an arbitrary packet size of 4k.

Reviewed by:	markj, Scott Phillips <d.scott.phillips@intel.com>
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D20308
---
 usr.sbin/bhyve/gdb.c | 65 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 64 insertions(+), 1 deletion(-)

diff --git a/usr.sbin/bhyve/gdb.c b/usr.sbin/bhyve/gdb.c
index 5d3fa6ff52a4..3571a4e2b604 100644
--- a/usr.sbin/bhyve/gdb.c
+++ b/usr.sbin/bhyve/gdb.c
@@ -992,6 +992,66 @@ command_equals(const uint8_t *data, size_t len, const char *cmd)
 	return (memcmp(data, cmd, strlen(cmd)) == 0);
 }
 
+static void
+check_features(const uint8_t *data, size_t len)
+{
+	char *feature, *next_feature, *str, *value;
+	bool supported;
+
+	str = malloc(len + 1);
+	memcpy(str, data, len);
+	str[len] = '\0';
+	next_feature = str;
+
+	while ((feature = strsep(&next_feature, ";")) != NULL) {
+		/*
+		 * Null features shouldn't exist, but skip if they
+		 * do.
+		 */
+		if (strcmp(feature, "") == 0)
+			continue;
+
+		/*
+		 * Look for the value or supported / not supported
+		 * flag.
+		 */
+		value = strchr(feature, '=');
+		if (value != NULL) {
+			*value = '\0';
+			value++;
+			supported = true;
+		} else {
+			value = feature + strlen(feature) - 1;
+			switch (*value) {
+			case '+':
+				supported = true;
+				break;
+			case '-':
+				supported = false;
+				break;
+			default:
+				/*
+				 * This is really a protocol error,
+				 * but we just ignore malformed
+				 * features for ease of
+				 * implementation.
+				 */
+				continue;
+			}
+			value = NULL;
+		}
+
+		/* No currently supported features. */
+	}
+	free(str);
+
+	start_packet();
+
+	/* This is an arbitrary limit. */
+	append_string("PacketSize=4096");
+	finish_packet();
+}
+
 static void
 gdb_query(const uint8_t *data, size_t len)
 {
@@ -999,7 +1059,6 @@ gdb_query(const uint8_t *data, size_t len)
 	/*
 	 * TODO:
 	 * - qSearch
-	 * - qSupported
 	 */
 	if (command_equals(data, len, "qAttached")) {
 		start_packet();
@@ -1037,6 +1096,10 @@ gdb_query(const uint8_t *data, size_t len)
 		start_packet();
 		append_char('l');
 		finish_packet();
+	} else if (command_equals(data, len, "qSupported")) {
+		data += strlen("qSupported");
+		len -= strlen("qSupported");
+		check_features(data, len);
 	} else if (command_equals(data, len, "qThreadExtraInfo")) {
 		char buf[16];
 		int tid;