[PATCH] D144392: [lldb] Skip signal handlers for ignored signals on lldb-server's side when stepping

[Pavel Kosov via Phabricator via llvm-commits]

kpdev42 added a comment.

1. There is a situation where the patch might go wrong. When stepping while inside:
  - a signal handler when `SA_NODEFER` flag is set (the same signal can be received while it is still being handled), and the signal is received again;
  - a handler that is set on multiple signals and they are not masked, and these signals are received one after another;
  - a handler that happens to call the current function

recursion happens and stopping at this specifically set up breakpoint on pc is not valid. With this patch this would result in unexpected stops, though this situation is very specific. Would it make sense to complicate this logic and store current `sp` or `fp` values from `NativeRegisterContext` and compare if they are the same?

2. The basic behavior is pretty easy to test by sending a lot of signals, but testing specific cases like setting the temporary breakpoint on an address where there is already another breakpoint is tough. One test was added for this, but it does not actually trigger the situation. This very much depends on when the signal is going to be received by the process, and it can't really be controlled.

3. This slightly changes 1 line of code in `NativeProcessFreeBSD`, but I don't have the means to test if it even compiles, though the logic should be equivalent.

4. When I looked at `NativeProcessFreeBSD`, it seems that software single stepping isn't even being set up there, just checked for when the process stops. As I can see from history, software single stepping with similar code was in the "legacy FreeBSD plugin" which was removed here: https://reviews.llvm.org/D96555 , and then single stepping with shared code was added to the new plugin here: https://reviews.llvm.org/D95802 . Because I couldn't find where the `SetupSoftwareSingleStepping` would be called for FreeBSD I didn't change that, but this probably should be addressed?


Repository:
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https://reviews.llvm.org/D144392