[Bug remote/28440] New: GDB sends vCont;s packets on targets that don't report support for single-stepping

[Bug remote/28440] New: GDB sends vCont;s packets on targets that don't report support for single-stepping

[danielprilik at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28440

            Bug ID: 28440
           Summary: GDB sends vCont;s packets on targets that don't report
                    support for single-stepping
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: remote
          Assignee: unassigned at sourceware dot org
          Reporter: danielprilik at gmail dot com
  Target Milestone: ---

On certain architectures, the GDB client doesn't seem to respect `vCont?`
responses that don't include `;s;S`, and will unconditionally send single-step
resume packets, even when the target has not explicitly acknowledges support.

e.g: when connected to a x86_64 target:

  Sending packet: $vCont?#49...Packet received: vCont;c;C
  Packet vCont (verbose-resume) is supported
  Sending packet: $vCont;s:p1.1;c:p1.-1#f7...Remote connection closed

Interestingly enough, this is _not_ the case for all architectures. When
connected to an `armv4t` target:

  Sending packet: $vCont?#49...Packet received: vCont;c;C
  Packet vCont (verbose-resume) is supported
  Sending packet: $m55550000,4#61...Packet received: 00000000
  Sending packet: $m55550000,4#61...Packet received: 00000000
  Sending packet: $m55550004,4#65...Packet received: 00000000
  Sending packet: $m55550000,4#61...Packet received: 00000000
  Sending packet: $m55550000,4#61...Packet received: 00000000
  Sending packet: $m55550000,4#61...Packet received: 00000000
  Sending packet: $Z0,55550004,4#ae...Packet received:
  Packet Z0 (software-breakpoint) is NOT supported
  Sending packet: $m55550004,4#65...Packet received: 00000000
  Sending packet: $X55550004,0:#86...Packet received: OK
  binary downloading supported by target
  Sending packet: $X55550004,4:\001\000\237�#19...Packet received: OK
  Sending packet: $vCont;c:p1.-1#0f

Which is what I would expect (i.e: it attempts to set a temporary software
breakpoint, and then continues the target).

* * *

While looking into this bug, I created a basic set of "dummy" remote targets to
figure out why this was happening. I've uploaded these targets to Github, in
hope that they can be useful while looking into this bug:

https://github.com/daniel5151/gdb-optional-step-bug

For more context, here is the (unrelated) issue where I stumbled across this
bug:

https://github.com/daniel5151/gdbstub/issues/89#issuecomment-939203794

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug remote/28440] GDB sends vCont;s packets on targets that don't report support for single-stepping

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28440

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-08-03
                 CC|                            |tromey at sourceware dot org
           Assignee|unassigned at sourceware dot org   |tromey at sourceware dot org
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
I think this is solved here:

https://sourceware.org/pipermail/gdb-patches/2023-June/200249.html

-- 
You are receiving this mail because:
You are on the CC list for the bug.