Re: [PATCH v2] Windows gdb: Fix resetting of the debug-registers bit in ContextFlags

[Hannes Domani <ssbssa@yahoo.de>]

 Ping.


Am Mittwoch, 22. Juli 2026 um 17:34:52 MESZ hat Hannes Domani <ssbssa@yahoo.de> Folgendes geschrieben:

> The CONTEXT_DEBUG_REGISTERS also includes the arch-specific bit
> (CONTEXT_i386 or CONTEXT_AMD64) which is included in all CONTEXT_*
> defines.
> 
> So this basically just checks if any CONTEXT_* define is set:
>   if ((context->ContextFlags & CONTEXT_DEBUG_REGISTERS) != 0)
> 
> And similarly, unsetting CONTEXT_DEBUG_REGISTERS removes the
> arch-specific bit as well.
> 
> This isn't a problem per-se, since Windows seems to just ignore the
> arch-specific bit anyways in SetThreadContext.
> But it also creates inconsistent behavior for WOW64, because it uses
> the wrong arch-specific bit there.
> 
> So this creates a CONTEXT_DEBUG_REG_FLAG define with just the
> debug-registers bit, and uses it in these problematic locations.
> ---
> v2:
>   - updated commit message
>   - changed CONTEXT_DEBUG_REG_FLAG define to avoid hardcoded number
> ---
> gdb/x86-windows-nat.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/gdb/x86-windows-nat.c b/gdb/x86-windows-nat.c
> index 27adeb1f154..2f556e47b39 100644
> --- a/gdb/x86-windows-nat.c
> +++ b/gdb/x86-windows-nat.c
> @@ -42,6 +42,10 @@ enum
> 
> #define DR6_CLEAR_VALUE 0xffff0ff0
> 
> +/* The CONTEXT_DEBUG_REGISTERS define without the arch-specific bit
> +  (CONTEXT_i386 or CONTEXT_AMD64).  */
> +#define CONTEXT_DEBUG_REG_FLAG (CONTEXT_DEBUG_REGISTERS & ~CONTEXT_CONTROL)
> +
> struct x86_windows_per_inferior : public windows_per_inferior
> {
>   /* The function to use in order to determine whether a register is
> @@ -142,7 +146,7 @@ x86_windows_nat_target::thread_context_continue (windows_thread_info *th,
>     {
>       windows_process->fill_thread_context (th);
> 
> -      gdb_assert ((context->ContextFlags & CONTEXT_DEBUG_REGISTERS) != 0);
> +      gdb_assert ((context->ContextFlags & CONTEXT_DEBUG_REG_FLAG) != 0);
> 
>       /* Check whether the thread has Dr6 set indicating a
>         watchpoint hit, and we haven't seen the watchpoint event
> @@ -173,13 +177,13 @@ x86_windows_nat_target::thread_context_continue (windows_thread_info *th,
>             update the debug registers later when the thread
>             is re-resumed by the core after the watchpoint
>             event.  */
> -          context->ContextFlags &= ~CONTEXT_DEBUG_REGISTERS;
> +          context->ContextFlags &= ~CONTEXT_DEBUG_REG_FLAG;
>         }
>         }
>       else
>         DEBUG_EVENTS ("0x%x has no dr6 set", th->tid);
> 
> -      if ((context->ContextFlags & CONTEXT_DEBUG_REGISTERS) != 0)
> +      if ((context->ContextFlags & CONTEXT_DEBUG_REG_FLAG) != 0)
>         {
>           DEBUG_EVENTS ("0x%x changing dregs", th->tid);
>           context->Dr0 = state->dr_mirror[0];
> -- 
> 2.54.0