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Date: Tue, 10 Mar 2009 15:09:50 +0100
From: Ingo Molnar <mingo@...e.hu>
To: prasad@...ux.vnet.ibm.com
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Alan Stern <stern@...land.harvard.edu>,
Roland McGrath <roland@...hat.com>
Subject: Re: [patch 02/11] x86 architecture implementation of Hardware
Breakpoint interfaces
* prasad@...ux.vnet.ibm.com <prasad@...ux.vnet.ibm.com> wrote:
> +/*
> + * Handle debug exception notifications.
> + */
> +
> +int __kprobes hw_breakpoint_handler(struct die_args *args)
> +{
> + struct cpu_hw_breakpoint *chbi;
> + int i;
> + struct hw_breakpoint *bp;
> + struct thread_hw_breakpoint *thbi = NULL;
> +
> + /* The DR6 value is stored in args->err */
> +#define DR6 (args->err)
that's ugly - what's wrong with an old-fashioned "int db6 =
args->err" type of approach?
> +
> + if (DR6 & DR_STEP)
> + return NOTIFY_DONE;
> +
> + chbi = &per_cpu(cpu_bp, get_cpu());
> +
> + /* Disable all breakpoints so that the callbacks can run without
> + * triggering recursive debug exceptions.
> + */
> + set_debugreg(0UL, 7);
> +
> + /* Assert that local interrupts are disabled
> + * Reset the DRn bits in the virtualized register value.
> + * The ptrace trigger routine will add in whatever is needed.
> + */
> + current->thread.vdr6 &= ~(DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3);
> +
> + /* Are we a victim of lazy debug-register switching? */
> + if (!chbi->bp_task)
> + ;
> + else if (chbi->bp_task != current) {
> +
> + /* No user breakpoints are valid. Perform the belated
> + * debug-register switch.
> + */
> + switch_to_none_hw_breakpoint();
> + } else {
> + thbi = chbi->bp_task->thread.hw_breakpoint_info;
> + }
> +
> + /* Handle all the breakpoints that were triggered */
> + for (i = 0; i < HB_NUM; ++i) {
> + if (likely(!(DR6 & (DR_TRAP0 << i))))
> + continue;
> +
> + /* Find the corresponding hw_breakpoint structure and
> + * invoke its triggered callback.
> + */
> + if (i < chbi->cur_kbpdata->num_kbps)
> + bp = chbi->cur_kbpdata->bps[i];
> + else if (thbi)
> + bp = thbi->bps[i];
> + else /* False alarm due to lazy DR switching */
> + continue;
> + if (bp) {
> + switch (bp->info.type) {
> + case HW_BREAKPOINT_WRITE:
> + case HW_BREAKPOINT_RW:
> + if (bp->triggered)
> + (bp->triggered)(bp, args->regs);
> + /* Re-enable the breakpoints */
> + set_debugreg(thbi ? thbi->tkdr7 :
> + chbi->cur_kbpdata->mkdr7, 7);
> + put_cpu_no_resched();
> +
> + return NOTIFY_STOP;
> + /*
> + * Presently we allow instruction breakpoints only in
> + * user-space when requested through ptrace.
> + */
> + case HW_BREAKPOINT_EXECUTE:
> + if (arch_check_va_in_userspace(bp->info.address,
> + current)) {
> + (bp->triggered)(bp, args->regs);
> + /* We'll return NOTIFY_DONE, do_debug will take care of the rest */
> + return NOTIFY_DONE;
> + }
> + }
the linebreaks here became so ugly because the whole loop body
should be moved inside a helper function.
> +++ linux-2.6-tip.hbkpt/arch/x86/include/asm/hw_breakpoint.h
> @@ -0,0 +1,132 @@
> +#ifndef _I386_HW_BREAKPOINT_H
> +#define _I386_HW_BREAKPOINT_H
> +
> +#ifdef __KERNEL__
> +#define __ARCH_HW_BREAKPOINT_H
> +
> +struct arch_hw_breakpoint {
> + char *name; /* Contains name of the symbol to set bkpt */
> + unsigned long address;
> + u8 len;
> + u8 type;
> +} __attribute__((packed));
hm, why packed and why u8 ? We dont expose this to user-space,
do we? (if yes then 'unsigned long' is wrong and __KERNEL__ is
wrong as well)
> +#include <linux/kdebug.h>
> +#include <asm-generic/hw_breakpoint.h>
> +
> +/* HW breakpoint accessor routines */
> +static inline const void *hw_breakpoint_get_kaddress(struct hw_breakpoint *bp)
> +{
> + return (const void *) bp->info.address;
> +}
> +
> +static inline const void __user *hw_breakpoint_get_uaddress
> + (struct hw_breakpoint *bp)
> +{
> + return (const void __user *) bp->info.address;
> +}
> +
> +static inline unsigned hw_breakpoint_get_len(struct hw_breakpoint *bp)
> +{
> + return bp->info.len;
> +}
> +
> +static inline unsigned hw_breakpoint_get_type(struct hw_breakpoint *bp)
> +{
> + return bp->info.type;
> +}
why this redirection, why dont just use the structure as-is? If
there's any arch weirdness then that arch should have
arch-special accessors - not the generic code.
> +
> +/* Kernel symbol lookup routine for installing Data HW Breakpoint Address */
> +static inline unsigned long hw_breakpoint_lookup_name(const char *name)
> +{
> + return kallsyms_lookup_name(name);
> +}
A wrapper around kallsyms_lookup_name() is quite pointless -
pleae us kallsyms_lookup_name() drectly.
> +/* Per-thread HW breakpoint and debug register info */
> +struct thread_hw_breakpoint {
> +
> + /* utrace support */
> + struct list_head node; /* Entry in thread list */
> + struct list_head thread_bps; /* Thread's breakpoints */
> + struct hw_breakpoint *bps[HB_NUM]; /* Highest-priority bps */
> + unsigned long tdr[HB_NUM]; /* and their addresses */
Please rename it to something like ->hw_breakpoint[] and
->address[] - 'bps' and 'tdr' look quite meaningless.
> + int num_installed; /* Number of installed bps */
> + unsigned gennum; /* update-generation number */
i suspect the gennum we can get rid of if we get rid of the
notion of priorities, right?
Ingo
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