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Fix gdb.base/watch-vfork.exp: Watchpoint triggers after vfork (sw) (timeout) with Linux 2.6.32 and older version

Browse Source 
https://sourceware.org/ml/gdb-patches/2014-04/msg00047.html

Got gdb.base/watch-vfork.exp: Watchpoint triggers after vfork (sw)
(timeout) with Linux 2.6.32 and older version.

The rootcause is after the test use "set can-use-hw-watchpoints 0" let GDB
doesn't use hardware breakpoint and set a watchpoint on "global", GDB
continue will keep single step inside function "vfork".
The Linux 2.6.32 and older version doesn't have commit
6580807da14c423f0d0a708108e6df6ebc8bc83d (get more info please goto
http://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=6580807da14c423f0d0a708108e6df6ebc8bc83d).
When the function "vfork" do syscall, the single step flag TIF_SINGLESTEP
will copy to child process.
Then GDB detach it, child process and parent process will be hanged.

So I make a patch that do a single step before detach.  Then TIF_SINGLESTEP
of child process in old Linux kernel will be cleared before detach.
Child process in new Linux kernel will not be affected by this single step.

2014-06-08  Hui Zhu  <hui@codesourcery.com>

	* common/linux-ptrace.c (linux_disable_event_reporting): New
	function.
	* common/linux-ptrace.h (linux_disable_event_reporting): New
	declaration.
	* linux-nat.c (linux_child_follow_fork): Do a single step before
	detach.
This commit is contained in:
Hui Zhu
2014-06-08 19:11:09 +08:00
parent ba2ffec396
commit c077881afa
4 changed files with 43 additions and 1 deletions
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25
gdb/linux-nat.c
View File

@ -414,6 +414,7 @@ holding the child stopped. Try \"set detach-on-fork\" or \
if (detach_fork)
{
struct cleanup *old_chain;
int status = 0;
/* Before detaching from the child, remove all breakpoints
from it. If we forked, then this has already been taken
@ -447,7 +448,29 @@ holding the child stopped. Try \"set detach-on-fork\" or \
if (linux_nat_prepare_to_resume != NULL)
linux_nat_prepare_to_resume (child_lp);
ptrace (PTRACE_DETACH, child_pid, 0, 0);
/* When debugging an inferior in an architecture that supports
hardware single stepping on a kernel without commit
6580807da14c423f0d0a708108e6df6ebc8bc83d, the vfork child
process starts with the TIF_SINGLESTEP/X86_EFLAGS_TF bits
set if the parent process had them set.
To work around this, single step the child process
once before detaching to clear the flags. */
if (!gdbarch_software_single_step_p (target_thread_architecture
(child_lp->ptid)))
{
int status;
linux_disable_event_reporting (child_pid);
if (ptrace (PTRACE_SINGLESTEP, child_pid, 0, 0) < 0)
perror_with_name (_("Couldn't do single step"));
if (my_waitpid (child_pid, &status, 0) < 0)
perror_with_name (_("Couldn't wait vfork process"));
}
if (WIFSTOPPED (status))
ptrace (PTRACE_DETACH, child_pid, 0, WSTOPSIG (status));
do_cleanups (old_chain);
}