[binutils-gdb] Workaround gdbserver<7.7 for setfs

[Jan Kratochvil <jkratoch at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=57809e5e5a506664eb54433ded81ab0785168a83

commit 57809e5e5a506664eb54433ded81ab0785168a83
Author: Jan Kratochvil <jan.kratochvil@redhat.com>
Date:   Wed Apr 27 21:27:40 2016 +0200

    Workaround gdbserver<7.7 for setfs
    
    With current FSF GDB HEAD and old FSF gdbserver I expected I could do:
    	gdb -ex 'file target:/root/redhat/threadit' -ex 'target remote :1234'
    (supplying that unsupported qXfer:exec-file:read by "file")
    But that does not work because:
    	Sending packet: $vFile:setfs:0#bf...Packet received: OK
    	Packet vFile:setfs (hostio-setfs) is supported
    	...
    	Sending packet: $vFile:setfs:104#24...Packet received: OK
    	"target:/root/redhat/threadit": could not open as an executable file: Invalid argument
    
    GDB documentation says:
    	The valid responses to Host I/O packets are:
    	An empty response indicates that this operation is not recognized.
    
    This "empty response" vs. "OK" was a bug in gdbserver < 7.7.  It was fixed by:
    	commit e7f0d979dd5cc4f8b658df892e93db69d6d660b7
    	Author: Yao Qi <yao@codesourcery.com>
    	Date:   Tue Dec 10 21:59:20 2013 +0800
    	    Fix a bug in matching notifications.
    	Message-ID: <1386684626-11415-1-git-send-email-yao@codesourcery.com>
    	https://sourceware.org/ml/gdb-patches/2013-12/msg00373.html
    	2013-12-10  Yao Qi  <yao@codesourcery.com>
    		* notif.c (handle_notif_ack): Return 0 if no notification
    		matches.
    
    with unpatched old FSF gdbserver and patched FSF GDB HEAD:
    	gdb -ex 'file target:/root/redhat/threadit' -ex 'target remote :1234'
    	Sending packet: $vFile:setfs:0#bf...Packet received: OK
    	Packet vFile:setfs (hostio-setfs) is NOT supported
    	...
    	(gdb) info sharedlibrary
    	From                To                  Syms Read   Shared Object Library
    	0x00007ffff7ddbae0  0x00007ffff7df627a  Yes (*)     target:/lib64/ld-linux-x86-64.so.2
    	0x00007ffff7bc48a0  0x00007ffff7bcf514  Yes (*)     target:/lib64/libpthread.so.0
    
    gdb/ChangeLog
    2016-04-26  Jan Kratochvil  <jan.kratochvil@redhat.com>
    
    	* remote.c (remote_start_remote): Detect PACKET_vFile_setfs.support.

Diff:
---
 gdb/ChangeLog |  4 ++++
 gdb/remote.c  | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 165c2a3..5cf8a5f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,7 @@
+2016-04-27  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* remote.c (remote_start_remote): Detect PACKET_vFile_setfs.support.
+
 2016-04-27  Martin Galvan  <martin.galvan@tallertechnologies.com>
 
 	* c-valprint.c (c_value_print): Always convert val back to reference
diff --git a/gdb/remote.c b/gdb/remote.c
index 4c18b4f..1f0d67c 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -4031,6 +4031,25 @@ remote_start_remote (int from_tty, struct target_ops *target, int extended_p)
   if (packet_support (PACKET_QAllow) != PACKET_DISABLE)
     remote_set_permissions (target);
 
+  /* gdbserver < 7.7 (before its fix from 2013-12-11) did reply to any
+     unknown 'v' packet with string "OK".  "OK" gets interpreted by GDB
+     as a reply to known packet.  For packet "vFile:setfs:" it is an
+     invalid reply and GDB would return error in
+     remote_hostio_set_filesystem, making remote files access impossible.
+     Disable "vFile:setfs:" in such case.  Do not disable other 'v' packets as
+     other "vFile" packets get correctly detected even on gdbserver < 7.7.  */
+  {
+    const char v_mustreplyempty[] = "vMustReplyEmpty";
+
+    putpkt (v_mustreplyempty);
+    getpkt (&rs->buf, &rs->buf_size, 0);
+    if (strcmp (rs->buf, "OK") == 0)
+      remote_protocol_packets[PACKET_vFile_setfs].support = PACKET_DISABLE;
+    else if (strcmp (rs->buf, "") != 0)
+      error (_("Remote replied unexpectedly to '%s': %s"), v_mustreplyempty,
+	     rs->buf);
+  }
+
   /* Next, we possibly activate noack mode.
 
      If the QStartNoAckMode packet configuration is set to AUTO,