Re: [FYI/pushed v4 08/25] Thread options & clone events (Linux GDBserver)

[Tom Tromey <tromey@adacore.com>]

>>>>> "Luis" == Luis Machado <luis.machado@arm.com> writes:

Luis> But find_process_pid returns nullptr. I wonder if it is one of those cases
Luis> where we have to deal with the tid rather than the pid.

Luis> Does this look like the same case you were chasing?

Yes.  The issue is that the new inferior isn't created until after the
new thread -- but the order can't really be reversed in the caller.

I've appended the patch.  I put off sending it because for internal
reasons it hasn't been through the AdaCore automated testing yet.
However, I did test it (using the AdaCore test suite -- not gdb's)
myself.

Let me know what you think.

Tom

commit 5464152cb1145bc1df108eb6904a642d8bc73b8c
Author: Tom Tromey <tromey@adacore.com>
Date:   Mon Feb 5 13:18:51 2024 -0700

    Fix crash in aarch64-linux gdbserver
    
    We noticed that aarch64-linux gdbserver will crash when the inferior
    vforks.  This happens in aarch64_get_debug_reg_state:
    
      struct process_info *proc = find_process_pid (pid);
    
      return &proc->priv->arch_private->debug_reg_state;
    
    Here, find_process_pid returns nullptr -- the new inferior hasn't yet
    been created in linux_process_target::handle_extended_wait.
    
    This patch fixes the problem by having aarch64_get_debug_reg_state
    return nullptr in this case, and then updating
    aarch64_linux_new_thread to check for this.

diff --git a/gdb/nat/aarch64-linux.c b/gdb/nat/aarch64-linux.c
index 5ebbc9b81f8..894de8aa3eb 100644
--- a/gdb/nat/aarch64-linux.c
+++ b/gdb/nat/aarch64-linux.c
@@ -81,9 +81,9 @@ aarch64_linux_new_thread (struct lwp_info *lwp)
   /* If there are hardware breakpoints/watchpoints in the process then mark that
      all the hardware breakpoint/watchpoint register pairs for this thread need
      to be initialized (with data from aarch_process_info.debug_reg_state).  */
-  if (aarch64_any_set_debug_regs_state (state, false))
+  if (state == nullptr || aarch64_any_set_debug_regs_state (state, false))
     DR_MARK_ALL_CHANGED (info->dr_changed_bp, aarch64_num_bp_regs);
-  if (aarch64_any_set_debug_regs_state (state, true))
+  if (state == nullptr || aarch64_any_set_debug_regs_state (state, true))
     DR_MARK_ALL_CHANGED (info->dr_changed_wp, aarch64_num_wp_regs);
 
   lwp_set_arch_private_info (lwp, info);
diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc
index 28d75d035dc..2a4f01a54da 100644
--- a/gdbserver/linux-aarch64-low.cc
+++ b/gdbserver/linux-aarch64-low.cc
@@ -403,7 +403,8 @@ struct aarch64_debug_reg_state *
 aarch64_get_debug_reg_state (pid_t pid)
 {
   struct process_info *proc = find_process_pid (pid);
-
+  if (proc == nullptr)
+    return nullptr;
   return &proc->priv->arch_private->debug_reg_state;
 }