Messages in this thread | | | Date | Tue, 10 Feb 2009 18:05:14 +0530 | From | "K.Prasad" <> | Subject | [Patch 0/10] Hardware Breakpoint interfaces - v2 |
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Hi Andrew and all,
Please find the patches that introduce interfaces to access Hardware Breakpoint (or watchpoint) registers and an arch-specific implementation for x86/x86_64 architecture. The earlier patchset (sent to you here: http://lkml.org/lkml/2009/1/29/36) generated some discussion over the employment of RCU synchronisation in the patchset. They're now resolved. The other changes over the previous patchset include:
- Modified kernel/hw_breakpoint.c and arch/x86/kernel/hw_breakpoint.c into independently compilable units. Made necessary declarations in header files.
- One pair of read-side RCU locks were introduced in load_debug_registers() following discussions about RCU synchronisation in the patchset.
A short description of the framework and interfaces is provided below. Some of the details will be specific to x86/x86_64 architecture and may vary depending upon the support provided by the target processor.
The patches are based of -mm tree (commit 6a522c468fe6d01679224edfe78586c95b6d9872) and have been tested on x86 architecture over 2.6.29-rc2. Kindly accept these patches to be a part of -mm tree.
Description ------------- The Hardware Breakpoint registers can be used for tracing changes to a variable or data location (even I/O ports in x86/x86_64) and will be extremely helpful in debugging problems such as memory corruption. While these registers have been used by user-space debuggers for long (through 'ptrace' syscalls), KGDB exploited them for kernel-space addresses.
The proposed framework, introduces interfaces to use them directly on both user- and kernel-space addresses apart from arbitrating requests from various such users for the limited number of registers.
The interfaces are:
int register_kernel_hw_breakpoint(struct hw_breakpoint *); void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp);
int register_user_hw_breakpoint(struct task_struct *tsk, struct hw_breakpoint *bp); void unregister_user_hw_breakpoint(struct task_struct *tsk, struct hw_breakpoint *bp);
The 'struct hw_breakpoint' will be the anchor data-structure containing all the necessary information such as name or address, type, length, priority and pointers to handler functions (some of which are arch-specific). More information about the role of each field, the handler functions and their return values can be found in the descriptive comments preceding these functions and in "include/asm-generic/hw_breakpoint.h".
While (un)register_user_hw_breakpoint() isn't exported yet, its worker-routine __register_user-hw_breakpoint() is used by ptrace syscall for all breakpoint register requirements. For the kernel-space, a simple use case to trace 'write' operations on a kernel variable can be found in samples/hw_breakpoint/data_breakpoint.c.
In the current patchset, support is provided only for read and read-write breakpoints on data locations, which can be later expand to include instruction and I/O breakpoints for x86/x86_64.
The patches are based on 2.6.29-rc2 and have been tested on an x86 machine along with concurrent sessions of a kprobe-module and a GDB session using HW breakpoints on the target program.
There is pending integration with 'KGDB' without which mutual exclusion between them (KGDB and HW breakpoint use through above interfaces) needs to be observed.
Thanks, K.Prasad
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