[Bug remote/22597] New: Empty `qsThreadInfo' reply handling regression causing inability to execute

["macro at linux-mips dot org" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=22597

            Bug ID: 22597
           Summary: Empty `qsThreadInfo' reply handling regression causing
                    inability to execute
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: remote
          Assignee: unassigned at sourceware dot org
          Reporter: macro@linux-mips.org
                CC: palves at redhat dot com
  Target Milestone: 8.1

At <https://sourceware.org/ml/gdb-patches/2017-12/msg00285.html>, I wrote:

On Tue, 12 Dec 2017, Maciej W. Rozycki wrote:

>  Another regression.  This makes `mips-mti-linux-gnu' GDB stop working 
> with older stubs.  I have discovered it in an attempt to regression-test 
> said GDB with a remote n64 target and `x86_64-pc-linux-gnu' host, and an 
> outstanding change which affects non-XML stubs.  Any attempt to continue 
> execution after the initial connection fails with:
> 
> [...]
> Process .../gdb/testsuite/outputs/gdb.base/advance/advance created; pid = 2670
> Listening on port 2346
> target remote [...]:2346
> Remote debugging using [...]:2346
> Reading symbols from .../lib64/ld.so.1...done.
> [Switching to Thread <main>]
> (gdb) continue
> Cannot execute this command without a live selected thread.
> (gdb) 
> 
> This is as from commit 5cd63fda035d.  Up to 5cd63fda035d^ instead I get:
> 
> [...]
> Process .../gdb/testsuite/outputs/gdb.base/advance/advance created; pid = 30044
> Listening on port 2346
> target remote [...]:2346
> Remote debugging using [...]:2346
> Reading symbols from .../lib64/ld.so.1...done.
> 0x000000fff79534f0 in __start () from .../lib64/ld.so.1
> (gdb) continue
> Continuing.
> warning: Could not load shared library symbols for linux-vdso.so.1.
> Do you need "set solib-search-path" or "set sysroot"?
> 
> Breakpoint 1, main () at .../gdb/testsuite/gdb.base/advance.c:41
> 41	  c = 5;
> (gdb) 
> 
> At the protocol level the difference starts here (bad):
> 
> Sending packet: $qfThreadInfo#bb...Ack
> Packet received: m1814
> Sending packet: $qsThreadInfo#c8...Ack
> Packet received: l
> [Switching to Thread <main>]
> Sending packet: $qSymbol::#5b...Ack
> Packet received: qSymbol:6e70746c5f76657273696f6e
> Sending packet: $qSymbol::6e70746c5f76657273696f6e#4d...Ack
> Packet received: OK
> Sending packet: $Hg1814#7d...Ack
> Packet received: OK
> Sending packet: $Hg0#df...Ack
> Packet received: E01
> (gdb) continue
> Cannot execute this command without a live selected thread.
> (gdb)
> 
> vs (good):
> 
> Sending packet: $qfThreadInfo#bb...Ack
> Packet received: m154d
> Sending packet: $qsThreadInfo#c8...Ack
> Packet received: l
> Sending packet: $mfff726c4f0,4#cb...Ack
> Packet received: 03e0c825
> Sending packet: $mfff726c4ec,4#fd...Ack
> Packet received: 00000000
> Sending packet: $mfff726c4f0,4#cb...Ack
> Packet received: 03e0c825
> 0x000000fff726c4f0 in __start () from .../lib64/ld.so.1
> Sending packet: $qSymbol::#5b...Ack
> Packet received: qSymbol:6e70746c5f76657273696f6e
> Sending packet: $qSymbol::6e70746c5f76657273696f6e#4d...Ack
> Packet received: OK
> (gdb) continue
> Continuing.
> Sending packet: $mfff726c4f0,4#cb...Ack
> Packet received: 03e0c825
> Sending packet: $Z0,120000d6c,4#36...Ack
> Packet received:
> Packet Z0 (software-breakpoint) is NOT supported
> [...]
> 
> The version of `gdbserver' causing this regression is as at commit 
> f8b73d13b7ca^, the last MIPS backend version with no XML support.  It's 
> likely that later versions hit this regression too, as the mode of failure 
> is clearly not XML-related.

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