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As Rajendra SY reported at <https://sourceware.org/ml/gdb-patches/2018-04/msg00399.html>, several attach-related tests are failing on FreeBSD. The "attach" command errors with "Couldn't get registers: Device busy". When the "attach" command is executed, it calls target_attach -> inf_ptrace_attach, which just does the ptrace(PT_ATTACH), it does not wait for the child to stop with SIGSTOP. Afterwards, the command is complete and we go back to the event loop. The event loop wakes up and we end up in target_wait -> fbsd_wait, and handle the SIGSTOP stop. At the end of execute_command, though, before going back to the event loop, we check if the frame language changed via check_frame_language_change(). That reads the current PC, which is what leads to the registers read that fails. The problem is that we fail to mark the attached-to thread as executing between the initial attach, and the subsequent target_wait. Until we see the thread stop with SIGSTOP, we shouldn't try to read registers off of it. I guess there may a timing issue here - if you're "lucky", the thread may stop before gdb reads its registers, masking the problem. With that fixed, check_frame_language_change() becomes a nop until the thread is marked not-executing again, after target_wait is called and we go through handle_inferior_event -> normal_stop. We haven't seen the problem on Linux because there, the target_attach implementation waits for the thread to stop before returning. Still, that's supposedly hidden from the core, since the Linux target, like most targets, is a '!to_attach_no_wait' target. This fixes: FAIL: gdb.base/attach.exp: attach1, after setting file FAIL: gdb.base/attach.exp: attach2, with no file FAIL: gdb.base/attach.exp: load file manually, after attach2 (re-read) (got interactive prompt) FAIL: gdb.base/attach.exp: attach when process' a.out not in cwd FAIL: gdb.base/dprintf-detach.exp: bai=on ds=gdb dd=on: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=on ds=gdb dd=off: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=on ds=call dd=on: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=on ds=call dd=off: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=on ds=agent dd=on: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=on ds=agent dd=off: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=off ds=gdb dd=on: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=off ds=gdb dd=off: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=off ds=call dd=on: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=off ds=call dd=off: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=off ds=agent dd=on: re-attach to inferior FAIL: gdb.base/dprintf-detach.exp: bai=off ds=agent dd=off: re-attach to inferior gdb/ChangeLog: 2018-04-21 Pedro Alves <palves@redhat.com> Rajendra SY <rajendra.sy@gmail.com> * inf-ptrace.c (inf_ptrace_attach): Mark the thread as executing. * remote.c (extended_remote_attach): In all-stop mode, mark the thread as executing.
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