[Qemu-devel] [Bug 1030666] [NEW] gdb can't proceed after a breakpoint

[Legorol]

Public bug reported:

Using qemu-1.0.1-windows.zip package from http://lassauge.free.fr/qemu/
Host: Windows 7 Ultimate 64-bit
Guest: i386 system running MS-DOS 6.22
Launch command line:
  qemu-system-i386.exe -L Bios -fda "DOS.vfd" -fdb "Data.vfd" -gdb 
tcp:127.0.0.1:1234
Debbugers tried:
  gdb 7.3.50.20111026-cvs running on Cygwin 1.7.16
  gdb 7.4 on MinGW

Short description:
I use gdb to attach to a running Qemu session, set a breakpoint and resume 
execution. When the breakpoint is hit, gdb gains control as expected. However, 
trying to single-step or continue at this point just causes the same breakpoint 
to be hit immediately again. Deleting the breakpoint allows single-stepping or 
continue to work.

Steps to reproduce:
DOS.vfd is a floppy image containing an MS-DOS 6.22 startup disk.
Data.vfd is a floppy image containing a single program (hello.com).
The aim is to debug the execution of hello.com with gdb.
Launch Qemu.
Launch gdb, an attach to qemu:
  "target remote localhost:1234"
I know the address at which hello.com will be loaded, so set a breakpoint there 
and resume execution:
  "break *0xf730"
  "continue"
In Qemu, start hello.com. The breakpoint is immediately hit, execution stops 
and gdb gains control.
Examining the program gives expected results (such as "info reg" or 
"disassemble").
At this point, try to proceed either with single-stepping ("si" or "ni") or 
with "continue", and the same breakpoint is immediately hit again. Subsequent 
attempts to single-step or continue just keep hitting the same breakpoint.
The only way to proceed at this point is to delete the breakpoint, after which 
both single-stepping and continue work.

Note that single-stepping and continue works as expected if it is done
after interrupting execution with Ctrl-C.

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: breakpoint gdb

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https://bugs.launchpad.net/bugs/1030666

Title:
  gdb can't proceed after a breakpoint

Status in QEMU:
  New

Bug description:
  Using qemu-1.0.1-windows.zip package from http://lassauge.free.fr/qemu/
  Host: Windows 7 Ultimate 64-bit
  Guest: i386 system running MS-DOS 6.22
  Launch command line:
    qemu-system-i386.exe -L Bios -fda "DOS.vfd" -fdb "Data.vfd" -gdb 
tcp:127.0.0.1:1234
  Debbugers tried:
    gdb 7.3.50.20111026-cvs running on Cygwin 1.7.16
    gdb 7.4 on MinGW

  Short description:
  I use gdb to attach to a running Qemu session, set a breakpoint and resume 
execution. When the breakpoint is hit, gdb gains control as expected. However, 
trying to single-step or continue at this point just causes the same breakpoint 
to be hit immediately again. Deleting the breakpoint allows single-stepping or 
continue to work.

  Steps to reproduce:
  DOS.vfd is a floppy image containing an MS-DOS 6.22 startup disk.
  Data.vfd is a floppy image containing a single program (hello.com).
  The aim is to debug the execution of hello.com with gdb.
  Launch Qemu.
  Launch gdb, an attach to qemu:
    "target remote localhost:1234"
  I know the address at which hello.com will be loaded, so set a breakpoint 
there and resume execution:
    "break *0xf730"
    "continue"
  In Qemu, start hello.com. The breakpoint is immediately hit, execution stops 
and gdb gains control.
  Examining the program gives expected results (such as "info reg" or 
"disassemble").
  At this point, try to proceed either with single-stepping ("si" or "ni") or 
with "continue", and the same breakpoint is immediately hit again. Subsequent 
attempts to single-step or continue just keep hitting the same breakpoint.
  The only way to proceed at this point is to delete the breakpoint, after 
which both single-stepping and continue work.

  Note that single-stepping and continue works as expected if it is done
  after interrupting execution with Ctrl-C.

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