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Re: [PATCH] Handle MIPS Linux SIGTRAP siginfo.si_code values
- From: "Maciej W. Rozycki" <macro at imgtec dot com>
- To: Pedro Alves <palves at redhat dot com>
- Cc: <gdb-patches at sourceware dot org>, "Maciej W. Rozycki" <macro at linux-mips dot org>
- Date: Wed, 24 Feb 2016 18:29:46 +0000
- Subject: Re: [PATCH] Handle MIPS Linux SIGTRAP siginfo.si_code values
- Authentication-results: sourceware.org; auth=none
- References: <1456332239-24007-1-git-send-email-palves at redhat dot com>
On Wed, 24 Feb 2016, Pedro Alves wrote:
> @@ -140,14 +140,32 @@ struct buffer;
> in SPU code on a Cell/B.E. However, SI_KERNEL is never seen
> on a SIGTRAP for any other reason.
>
> - The generic Linux target code should use GDB_ARCH_IS_TRAP_BRKPT
> - instead of TRAP_BRKPT to abstract out these peculiarities. */
> + The MIPS kernel uses SI_KERNEL for all kernel generated traps.
> + Since:
> +
> + - MIPS doesn't do hardware single-step
> + - We don't need to care about exec SIGTRAPs, since we assume
> + PTRACE_EVENT_EXEC.
> + - The MIPS kernel doesn't support hardware breakpoints.
> +
> + on MIPS, all we need to care about is distinguishing between
> + software breakpoints and hardware watchpoints, which can be done by
> + peeking the debug registers.
I'm assuming spurious traps such as from trap instructions will still be
delivered as such, right?
> +
> + The generic Linux target code should use GDB_ARCH_IS_TRAP_* instead
> + of TRAP_* to abstract out these peculiarities. */
> #if defined __i386__ || defined __x86_64__
> # define GDB_ARCH_IS_TRAP_BRKPT(X) ((X) == SI_KERNEL)
> +# define GDB_ARCH_IS_TRAP_HWBKPT(X) ((X) == TRAP_HWBKPT)
> #elif defined __powerpc__
> # define GDB_ARCH_IS_TRAP_BRKPT(X) ((X) == SI_KERNEL || (X) == TRAP_BRKPT)
> +# define GDB_ARCH_IS_TRAP_HWBKPT(X) ((X) == TRAP_HWBKPT)
> +#elif defined __mips__
> +# define GDB_ARCH_IS_TRAP_BRKPT(X) ((X) == SI_KERNEL)
> +# define GDB_ARCH_IS_TRAP_HWBKPT(X) ((X) == SI_KERNEL)
Shall I add the TRAP_BRKPT and TRAP_HWBKPT codes to the MIPS Linux kernel
then or not? If anything, this looks like a performance win to me, at no
significant cost (any possible kernel overhead will be in the range of a
couple processor instructions, which is nothing compared to an extra
ptrace(2) call and all the associated processing).
Maciej