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SubjectRe: [PATCH 10/15] powerpc/watchpoint: Use loop for thread_struct->ptrace_bps
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Le 09/03/2020 à 09:58, Ravi Bangoria a écrit :
> ptrace_bps is already an array of size HBP_NUM_MAX. But we use
> hardcoded index 0 while fetching/updating it. Convert such code
> to loop over array.
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
> ---
> arch/powerpc/kernel/hw_breakpoint.c | 7 +++++--
> arch/powerpc/kernel/process.c | 6 +++++-
> arch/powerpc/kernel/ptrace.c | 28 +++++++++++++++++++++-------
> 3 files changed, 31 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
> index f4d48f87dcb8..b27aca623267 100644
> --- a/arch/powerpc/kernel/hw_breakpoint.c
> +++ b/arch/powerpc/kernel/hw_breakpoint.c
> @@ -419,10 +419,13 @@ NOKPROBE_SYMBOL(hw_breakpoint_exceptions_notify);
> */
> void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
> {
> + int i;
> struct thread_struct *t = &tsk->thread;
>
> - unregister_hw_breakpoint(t->ptrace_bps[0]);
> - t->ptrace_bps[0] = NULL;
> + for (i = 0; i < nr_wp_slots(); i++) {
> + unregister_hw_breakpoint(t->ptrace_bps[i]);
> + t->ptrace_bps[i] = NULL;
> + }
> }
>
> void hw_breakpoint_pmu_read(struct perf_event *bp)
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 42ff62ef749c..b9ab740fcacf 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -1628,6 +1628,9 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
> void (*f)(void);
> unsigned long sp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
> struct thread_info *ti = task_thread_info(p);
> +#ifdef CONFIG_HAVE_HW_BREAKPOINT
> + int i;
> +#endif

Could we avoid all those #ifdefs ?

I think if we make p->thread.ptrace_bps[] exist all the time, with a
size of 0 when CONFIG_HAVE_HW_BREAKPOINT is not set, then we can drop a
lot of #ifdefs.

>
> klp_init_thread_info(p);
>
> @@ -1687,7 +1690,8 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
> p->thread.ksp_limit = (unsigned long)end_of_stack(p);
> #endif
> #ifdef CONFIG_HAVE_HW_BREAKPOINT
> - p->thread.ptrace_bps[0] = NULL;
> + for (i = 0; i < nr_wp_slots(); i++)
> + p->thread.ptrace_bps[i] = NULL;
> #endif
>
> p->thread.fp_save_area = NULL;
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index f6d7955fc61e..e2651f86d56f 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c

You'll have to rebase all this on the series
https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=161356
which is about to go into powerpc-next

> @@ -2829,6 +2829,19 @@ static int set_dac_range(struct task_struct *child,
> }
> #endif /* CONFIG_PPC_ADV_DEBUG_DAC_RANGE */
>
> +#ifdef CONFIG_HAVE_HW_BREAKPOINT
> +static int empty_ptrace_bp(struct thread_struct *thread)
> +{
> + int i;
> +
> + for (i = 0; i < nr_wp_slots(); i++) {
> + if (!thread->ptrace_bps[i])
> + return i;
> + }
> + return -1;
> +}
> +#endif

What does this function do exactly ? I seems to do more than what its
name suggests.

> +
> #ifndef CONFIG_PPC_ADV_DEBUG_REGS
> static int empty_hw_brk(struct thread_struct *thread)
> {
> @@ -2915,8 +2928,9 @@ static long ppc_set_hwdebug(struct task_struct *child,
> len = 1;
> else
> return -EINVAL;
> - bp = thread->ptrace_bps[0];
> - if (bp)
> +
> + i = empty_ptrace_bp(thread);
> + if (i < 0)
> return -ENOSPC;
>
> /* Create a new breakpoint request if one doesn't exist already */
> @@ -2925,14 +2939,14 @@ static long ppc_set_hwdebug(struct task_struct *child,
> attr.bp_len = len;
> arch_bp_generic_fields(brk.type, &attr.bp_type);
>
> - thread->ptrace_bps[0] = bp = register_user_hw_breakpoint(&attr,
> + thread->ptrace_bps[i] = bp = register_user_hw_breakpoint(&attr,
> ptrace_triggered, NULL, child);
> if (IS_ERR(bp)) {
> - thread->ptrace_bps[0] = NULL;
> + thread->ptrace_bps[i] = NULL;
> return PTR_ERR(bp);
> }
>
> - return 1;
> + return i + 1;
> #endif /* CONFIG_HAVE_HW_BREAKPOINT */
>
> if (bp_info->addr_mode != PPC_BREAKPOINT_MODE_EXACT)
> @@ -2979,10 +2993,10 @@ static long ppc_del_hwdebug(struct task_struct *child, long data)
> return -EINVAL;
>
> #ifdef CONFIG_HAVE_HW_BREAKPOINT
> - bp = thread->ptrace_bps[0];
> + bp = thread->ptrace_bps[data - 1];

Is data checked somewhere to ensure it is not out of boundaries ? Or are
we sure it is always within ?

> if (bp) {
> unregister_hw_breakpoint(bp);
> - thread->ptrace_bps[0] = NULL;
> + thread->ptrace_bps[data - 1] = NULL;
> } else
> ret = -ENOENT;
> return ret;
>


Christophe

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