gdbstub: add support to Xfer:auxv:read: packet

This allows gdb to access the target’s auxiliary vector,
which can be helpful for telling system libraries important details
about the hardware, operating system, and process.

Signed-off-by: Lirong Yuan <yuanzi@google.com>
[AJB: minor tweaks to test case, update MAINTAINERS, restrict to Linux]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200730193932.3654677-1-yuanzi@google.com>
Message-Id: <20210108224256.2321-7-alex.bennee@linaro.org>

MAINTAINERS

@@ -2322,6 +2322,7 @@ R: Philippe Mathieu-Daudé <philmd@redhat.com>
 S: Maintained
 F: gdbstub*
 F: gdb-xml/
+F: tests/tcg/multiarch/gdbstub/
 
 Memory API
 M: Paolo Bonzini <pbonzini@redhat.com>

gdbstub.c

@@ -2172,6 +2172,12 @@ static void handle_query_supported(GdbCmdContext *gdb_ctx, void *user_ctx)
             ";ReverseStep+;ReverseContinue+");
     }
 
+#ifdef CONFIG_USER_ONLY
+    if (gdbserver_state.c_cpu->opaque) {
+        g_string_append(gdbserver_state.str_buf, ";qXfer:auxv:read+");
+    }
+#endif
+
     if (gdb_ctx->num_params &&
         strstr(gdb_ctx->params[0].data, "multiprocess+")) {
         gdbserver_state.multiprocess = true;
@@ -2233,6 +2239,46 @@ static void handle_query_xfer_features(GdbCmdContext *gdb_ctx, void *user_ctx)
                       gdbserver_state.str_buf->len, true);
 }
 
+#if defined(CONFIG_USER_ONLY) && defined(CONFIG_LINUX_USER)
+static void handle_query_xfer_auxv(GdbCmdContext *gdb_ctx, void *user_ctx)
+{
+    TaskState *ts;
+    unsigned long offset, len, saved_auxv, auxv_len;
+    const char *mem;
+
+    if (gdb_ctx->num_params < 2) {
+        put_packet("E22");
+        return;
+    }
+
+    offset = gdb_ctx->params[0].val_ul;
+    len = gdb_ctx->params[1].val_ul;
+    ts = gdbserver_state.c_cpu->opaque;
+    saved_auxv = ts->info->saved_auxv;
+    auxv_len = ts->info->auxv_len;
+    mem = (const char *)(saved_auxv + offset);
+    if (offset > auxv_len) {
+        put_packet("E00");
+        return;
+    }
+
+    if (len > (MAX_PACKET_LENGTH - 5) / 2) {
+        len = (MAX_PACKET_LENGTH - 5) / 2;
+    }
+
+    if (len < auxv_len - offset) {
+        g_string_assign(gdbserver_state.str_buf, "m");
+        memtox(gdbserver_state.str_buf, mem, len);
+    } else {
+        g_string_assign(gdbserver_state.str_buf, "l");
+        memtox(gdbserver_state.str_buf, mem, auxv_len - offset);
+    }
+
+    put_packet_binary(gdbserver_state.str_buf->str,
+                      gdbserver_state.str_buf->len, true);
+}
+#endif
+
 static void handle_query_attached(GdbCmdContext *gdb_ctx, void *user_ctx)
 {
     put_packet(GDB_ATTACHED);
@@ -2338,6 +2384,14 @@ static GdbCmdParseEntry gdb_gen_query_table[] = {
         .cmd_startswith = 1,
         .schema = "s:l,l0"
     },
+#if defined(CONFIG_USER_ONLY) && defined(CONFIG_LINUX_USER)
+    {
+        .handler = handle_query_xfer_auxv,
+        .cmd = "Xfer:auxv:read::",
+        .cmd_startswith = 1,
+        .schema = "l,l0"
+    },
+#endif
     {
         .handler = handle_query_attached,
         .cmd = "Attached:",

tests/tcg/multiarch/Makefile.target

@@ -55,6 +55,15 @@ run-gdbstub-sha1: sha1
 	"basic gdbstub support")
 
 EXTRA_RUNS += run-gdbstub-sha1
+
+run-gdbstub-qxfer-auxv-read: sha1
+	$(call run-test, $@, $(GDB_SCRIPT) \
+		--gdb $(HAVE_GDB_BIN) \
+		--qemu $(QEMU) --qargs "$(QEMU_OPTS)" \
+		--bin $< --test $(MULTIARCH_SRC)/gdbstub/test-qxfer-auxv-read.py, \
+	"basic gdbstub qXfer:auxv:read support")
+
+EXTRA_RUNS += run-gdbstub-sha1 run-gdbstub-qxfer-auxv-read
 endif
 
 

tests/tcg/multiarch/gdbstub/test-qxfer-auxv-read.py

@@ -0,0 +1,57 @@
+from __future__ import print_function
+#
+# Test auxiliary vector is loaded via gdbstub
+#
+# This is launched via tests/guest-debug/run-test.py
+#
+
+import gdb
+import sys
+
+failcount = 0
+
+def report(cond, msg):
+    "Report success/fail of test"
+    if cond:
+        print ("PASS: %s" % (msg))
+    else:
+        print ("FAIL: %s" % (msg))
+        global failcount
+        failcount += 1
+
+def run_test():
+    "Run through the tests one by one"
+
+    auxv = gdb.execute("info auxv", False, True)
+    report(isinstance(auxv, str), "Fetched auxv from inferior")
+    report(auxv.find("sha1"), "Found test binary name in auxv")
+
+#
+# This runs as the script it sourced (via -x, via run-test.py)
+#
+try:
+    inferior = gdb.selected_inferior()
+    arch = inferior.architecture()
+    print("ATTACHED: %s" % arch.name())
+except (gdb.error, AttributeError):
+    print("SKIPPING (not connected)", file=sys.stderr)
+    exit(0)
+
+if gdb.parse_and_eval('$pc') == 0:
+    print("SKIP: PC not set")
+    exit(0)
+
+try:
+    # These are not very useful in scripts
+    gdb.execute("set pagination off")
+    gdb.execute("set confirm off")
+
+    # Run the actual tests
+    run_test()
+except (gdb.error):
+    print ("GDB Exception: %s" % (sys.exc_info()[0]))
+    failcount += 1
+    pass
+
+print("All tests complete: %d failures" % failcount)
+exit(failcount)