[Bug gdb/23020] New: GDB gets stopped by SIGTTOU when breakpoint insertion in fork child fails

["simon.marchi at ericsson dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=23020

            Bug ID: 23020
           Summary: GDB gets stopped by SIGTTOU when breakpoint insertion
                    in fork child fails
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: simon.marchi at ericsson dot com
  Target Milestone: ---

This bug started with commit e671cd59d74c ("Per-inferior target_terminal state,
fix PR gdb/13211, more").  Here's how I can reproduce:

$ cat test.c
#include <unistd.h>

static void
break_here ()
{
}

int
main (int argc, char *argv[])
{
  fork ();

  break_here();

  return 0;
}
$ gcc test.c -g3 -O0 -o test -pie
$ ./gdb -nx -q --data-directory=data-directory test -ex "set detach-on-fork
off" -ex "b break_here" -ex "set non-stop on"
Reading symbols from test...done.
Breakpoint 1 at 0x64e: file test.c, line 6.
(gdb) r
Starting program: /home/simark/build/binutils-gdb-one-target/gdb/test 
[New process 1465]
Reading symbols from
/home/simark/build/binutils-gdb-one-target/gdb/test...done.
[2]  + 1451 suspended (tty output)  ./gdb -nx -q
--data-directory=data-directory test -ex "set detach-on-fork off
$ fg
[2]  - 1451 continued  ./gdb -nx -q --data-directory=data-directory test -ex
"set detach-on-fork off
Warning:
Cannot insert breakpoint 1.
Cannot access memory at address 0x64a

(gdb) 


To be clear, the bug here is that GDB gets stopped by SIGTTOU.  The fact that
the breakpoint fails to be inserted is another bug that should get looked at
separately.  It just happens to trigger the terminal output bug.

I suspect that GDB tries to do some output while the terminal is owned by the
inferior.

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