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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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