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authorSimon Marchi <simon.marchi@polymtl.ca>2021-05-28 17:28:35 -0400
committerSimon Marchi <simon.marchi@polymtl.ca>2021-08-03 20:26:49 -0400
commit82d1f134cc0908e80555ddad58b4d370ff2a76c2 (patch)
tree2e20122b928666132ac03eb626c2191f0bacb0a9 /gdb/target.h
parent814be17cf94319891ff8343a8441f8a4ecf11567 (diff)
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gdb: follow-fork: push target and add thread in target_follow_fork
In the context of ROCm-gdb [1], the ROCm target sits on top of the linux-nat target. when a process forks, it needs to carry over some data from the forking inferior to the fork child inferior. Ideally, the ROCm target would implement the follow_fork target_ops method, but there are some small problems. This patch fixes these, which helps the ROCm target, but also makes things more consistent and a bit nicer in general, I believe. The main problem is: when follow-fork-mode is "parent", target_follow_fork is called with the parent as the current inferior. When it's "child", target_follow_fork is called with the child as the current inferior. This means that target_follow_fork is sometimes called on the parent's target stack and sometimes on the child's target stack. The parent's target stack may contain targets above the process target, such as the ROCm target. So if follow-fork-child is "parent", the ROCm target would get notified of the fork and do whatever is needed. But the child's target stack, at that moment, only contains the exec and process target copied over from the parent. The child's target stack is set up by follow_fork_inferior, before calling target_follow_fork. In that case, the ROCm target wouldn't get notified of the fork. For consistency, I think it would be good to always call target_follow_fork on the parent inferior's target stack. I think it makes sense as a way to indicate "this inferior has called fork, do whatever is needed". The desired outcome of the fork (whether an inferior is created for the child, do we need to detach from the child) can be indicated by passed parameter. I therefore propose these changes: - make follow_fork_inferior always call target_follow_fork with the parent as the current inferior. That lets all targets present on the parent's target stack do some fork-related handling and push themselves on the fork child's target stack if needed. For this purpose, pass the child inferior down to target_follow_fork and follow_fork implementations. This is nullptr if no inferior is created for the child, because we want to detach from it. - as a result, in follow_fork_inferior, detach from the parent inferior (if needed) only after the target_follow_fork call. This is needed because we want to call target_follow_fork before the parent's target stack is torn down. - hand over to the targets in the parent's target stack (including the process target) the responsibility to push themselves, if needed, to the child's target stack. Also hand over the responsibility to the process target, at the same time, to create the child's initial thread (just like we do for follow_exec). - pass the child inferior to exec_on_vfork, so we don't need to swap the current inferior between parent and child. Nothing in exec_on_vfork depends on the current inferior, after this change. Although this could perhaps be replaced with just having the exec target implement follow_fork and push itself in the child's target stack, like the process target does... We would just need to make sure the process target calls beneath()->follow_fork(...). I'm not sure about this one. gdb/ChangeLog: * target.h (struct target_ops) <follow_fork>: Add inferior* parameter. (target_follow_fork): Likewise. * target.c (default_follow_fork): Likewise. (target_follow_fork): Likewise. * fbsd-nat.h (class fbsd_nat_target) <follow_fork>: Likewise. (fbsd_nat_target::follow_fork): Likewise, and call inf_ptrace_target::follow_fork. * linux-nat.h (class linux_nat_target) <follow_fork>: Likewise. * linux-nat.c (linux_nat_target::follow_fork): Likewise, and call inf_ptrace_target::follow_fork. * obsd-nat.h (obsd_nat_target) <follow_fork>: Likewise. * obsd-nat.c (obsd_nat_target::follow_fork): Likewise, and call inf_ptrace_target::follow_fork. * remote.c (class remote_target) <follow_fork>: Likewise. (remote_target::follow_fork): Likewise, and call process_stratum_target::follow_fork. * process-stratum-target.h (class process_stratum_target) <follow_fork>: New. * process-stratum-target.c (process_stratum_target::follow_fork): New. * target-delegates.c: Re-generate. [1] https://github.com/ROCm-Developer-Tools/ROCgdb Change-Id: I460bd0af850f0485e8aed4b24c6d8262a4c69929
Diffstat (limited to 'gdb/target.h')
-rw-r--r--gdb/target.h7
1 files changed, 4 insertions, 3 deletions
diff --git a/gdb/target.h b/gdb/target.h
index 5ba73f4..57afebe 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -636,7 +636,7 @@ struct target_ops
TARGET_DEFAULT_RETURN (1);
virtual int remove_vfork_catchpoint (int)
TARGET_DEFAULT_RETURN (1);
- virtual void follow_fork (ptid_t, target_waitkind, bool, bool)
+ virtual void follow_fork (inferior *, ptid_t, target_waitkind, bool, bool)
TARGET_DEFAULT_FUNC (default_follow_fork);
virtual int insert_exec_catchpoint (int)
TARGET_DEFAULT_RETURN (1);
@@ -1719,8 +1719,9 @@ extern int target_remove_vfork_catchpoint (int pid);
bookkeeping and fiddling necessary to continue debugging either the parent,
the child or both. */
-void target_follow_fork (ptid_t child_ptid, target_waitkind fork_kind,
- bool follow_child, bool detach_fork);
+void target_follow_fork (inferior *inf, ptid_t child_ptid,
+ target_waitkind fork_kind, bool follow_child,
+ bool detach_fork);
/* Handle the target-specific bookkeeping required when the inferior makes an
exec call.