Re: [RFC][PATCH 1/5] hw-breakpoints: Make kernel breakpoints APItruly generic

From: Mathieu Desnoyers
Date: Mon Jul 20 2009 - 13:28:10 EST


* Frederic Weisbecker (fweisbec@xxxxxxxxx) wrote:
[...]
> diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c
> index c1f64e6..015fec6 100644
> --- a/kernel/hw_breakpoint.c
> +++ b/kernel/hw_breakpoint.c
> @@ -297,15 +297,21 @@ EXPORT_SYMBOL_GPL(unregister_user_hw_breakpoint);
> /**
> * register_kernel_hw_breakpoint - register a hardware breakpoint for kernel space
> * @bp: the breakpoint structure to register
> - *
> - * @bp.info->name or @bp.info->address, @bp.info->len, @bp.info->type and
> + * @addr: the address where we want to set the breakpoint
> + * @len: length of the value in memory to break in
> + * @type: the type of the breakpoint (read/write/execute)
> * @bp->triggered must be set properly before invocation

Hi Frederic,

I think one of the great addition in this patchset is to allow using
breakpoints from arch-agnostic code.

It becomes important to document the error values which can be returned
by register_kernel_hw_breakpoint, so this will serve as guidelines for
architecture-specific arch_fill_hw_breakpoint() implementation. This
will become increasingly important, as this abstraction layer will
basically be responsible for either:

- Finding the best support the architecture can provide for a given hw
breakpoint.
- Failing with an explicit error value telling the in-kernel user why it
failed (e.g. if it must use a fallback, or return the error to the
user).

Maybe we should think of a more flexible breakpoint type mapping too,
e.g.:

monitor _strictly_ execute operation on address 0x...
-> would fail if the architecture does not support execution access
monitoring
monitor (at least) execute operations on address 0x...
-> would be allowed to use a more general monitor (e.g. RWX) if the
architecture does not support "execute only" monitor.

(same for read and write)

Mathieu

> *
> */
> -int register_kernel_hw_breakpoint(struct hw_breakpoint *bp)
> +int register_kernel_hw_breakpoint(struct hw_breakpoint *bp, unsigned long addr,
> + int len, enum breakpoint_type type)
> {
> int rc;
>
> + rc = arch_fill_hw_breakpoint(bp, addr, len, type);
> + if (rc)
> + return rc;
> +
> rc = arch_validate_hwbkpt_settings(bp, NULL);
> if (rc)
> return rc;
--
Mathieu Desnoyers
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