On GNU/Linux, if a pthreaded program has a thread call clone(CLONE_VM) directly, and then that clone LWP hits a debug event (breakpoint, etc.) GDB internal errors. Threaded programs shouldn't really be calling clone directly, but GDB shouldn't crash either. On GDB 7.9, the crash looks like: (gdb) break clone_fn Breakpoint 2 at 0x4007d8: file clone-thread_db.c, line 35. (gdb) r ... [Thread debugging using libthread_db enabled] ... /home/pedro/gdb/mygit/src/gdb/linux-nat.c:1030: internal-error: lin_lwp_attach_lwp: Assertion `lwpid > 0' failed. A problem internal to GDB has been detected, further debugging may prove unreliable. On earlier releases, it looked like this: (gdb) b clone_fn Breakpoint 1 at 0x4007d8: file clone-thread_db.c, line 35. (gdb) r ... [Thread debugging using libthread_db enabled] ... [New Thread 0x7ffff7fc2700 (LWP 3886)] ../../gdb/linux-thread-db.c:437: internal-error: thread_get_info_callback: Assertion `inout->thread_info != NULL' failed. A problem internal to GDB has been detected, further debugging may prove unreliable.
Mine.
The master branch has been updated by Pedro Alves <palves@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=5c5019c27c5a4a73ec53281b4b69044f82b179f0 commit 5c5019c27c5a4a73ec53281b4b69044f82b179f0 Author: Pedro Alves <palves@redhat.com> Date: Fri Feb 20 19:00:21 2015 +0000 PR18006: internal error if threaded program calls clone(CLONE_VM) On GNU/Linux, if a pthreaded program has a thread call clone(CLONE_VM) directly, and then that clone LWP hits a debug event (breakpoint, etc.) GDB internal errors. Threaded programs shouldn't really be calling clone directly, but GDB shouldn't crash either. The crash looks like this: (gdb) break clone_fn Breakpoint 2 at 0x4007d8: file clone-thread_db.c, line 35. (gdb) r ... [Thread debugging using libthread_db enabled] ... src/gdb/linux-nat.c:1030: internal-error: lin_lwp_attach_lwp: Assertion `lwpid > 0' failed. A problem internal to GDB has been detected, further debugging may prove unreliable. The problem is that 'clone' ends up clearing the parent thread's tid field in glibc's thread data structure. For x86_64, the glibc code in question is here: sysdeps/unix/sysv/linux/x86_64/clone.S: ... testq $CLONE_THREAD, %rdi jne 1f testq $CLONE_VM, %rdi movl $-1, %eax <---- jne 2f movl $SYS_ify(getpid), %eax syscall 2: movl %eax, %fs:PID movl %eax, %fs:TID <---- 1: When GDB refreshes the thread list out of libthread_db, it finds a thread with LWP with pid -1 (the clone's parent), which naturally isn't yet on the thread list. GDB then tries to attach to that bogus LWP id, which is caught by that assertion. The fix is to detect the bad PID early. Tested on x86-64 Fedora 20. GDBserver doesn't need any fix. gdb/ChangeLog: 2015-02-20 Pedro Alves <palves@redhat.com> PR threads/18006 * linux-thread-db.c (thread_get_info_callback): Return early if the thread's lwp id is -1. gdb/testsuite/ChangeLog: 2015-02-20 Pedro Alves <palves@redhat.com> PR threads/18006 * gdb.threads/clone-thread_db.c: New file. * gdb.threads/clone-thread_db.exp: New file.
Fixed.