Re: [PATCH -tip -v10 5/7] x86: add pt_regs register and stack access APIs

[Frederic Weisbecker <fweisbec at gmail dot com>]

On Tue, Jun 30, 2009 at 09:09:11PM -0400, Masami Hiramatsu wrote:
> Add following APIs for accessing registers and stack entries from pt_regs.
> 
> - regs_query_register_offset(const char *name)
>    Query the offset of "name" register.
> 
> - regs_query_register_name(unsigned offset)
>    Query the name of register by its offset.
> 
> - regs_get_register(struct pt_regs *regs, unsigned offset)
>    Get the value of a register by its offset.
> 
> - regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
>    Check the address is in the kernel stack.
> 
> - regs_get_kernel_stack_nth(struct pt_regs *reg, unsigned nth)
>    Get Nth entry of the kernel stack. (N >= 0)
> 
> - regs_get_argument_nth(struct pt_regs *reg, unsigned nth)
>    Get Nth argument at function call. (N >= 0)
> 
> Changes from v9:
>  -Fix a typo in a comment.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Roland McGrath <roland@redhat.com>
> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Cc: linux-arch@vger.kernel.org



Looks good!

Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>

Frederic.



> ---
> 
>  arch/x86/include/asm/ptrace.h |  122 +++++++++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/ptrace.c      |   73 +++++++++++++++++++++++++
>  2 files changed, 195 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
> index 0f0d908..d5e3b3b 100644
> --- a/arch/x86/include/asm/ptrace.h
> +++ b/arch/x86/include/asm/ptrace.h
> @@ -7,6 +7,7 @@
>  
>  #ifdef __KERNEL__
>  #include <asm/segment.h>
> +#include <asm/page_types.h>
>  #endif
>  
>  #ifndef __ASSEMBLY__
> @@ -216,6 +217,127 @@ static inline unsigned long user_stack_pointer(struct pt_regs *regs)
>  	return regs->sp;
>  }
>  
> +/* Query offset/name of register from its name/offset */
> +extern int regs_query_register_offset(const char *name);
> +extern const char *regs_query_register_name(unsigned offset);
> +#define MAX_REG_OFFSET (offsetof(struct pt_regs, ss))
> +
> +/**
> + * regs_get_register() - get register value from its offset
> + * @regs:	pt_regs from which register value is gotten.
> + * @offset:	offset number of the register.
> + *
> + * regs_get_register returns the value of a register whose offset from @regs
> + * is @offset. The @offset is the offset of the register in struct pt_regs.
> + * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
> + */
> +static inline unsigned long regs_get_register(struct pt_regs *regs,
> +					      unsigned offset)
> +{
> +	if (unlikely(offset > MAX_REG_OFFSET))
> +		return 0;
> +	return *(unsigned long *)((unsigned long)regs + offset);
> +}
> +
> +/**
> + * regs_within_kernel_stack() - check the address in the stack
> + * @regs:	pt_regs which contains kernel stack pointer.
> + * @addr:	address which is checked.
> + *
> + * regs_within_kenel_stack() checks @addr is within the kernel stack page(s).
> + * If @addr is within the kernel stack, it returns true. If not, returns false.
> + */
> +static inline int regs_within_kernel_stack(struct pt_regs *regs,
> +					   unsigned long addr)
> +{
> +	return ((addr & ~(THREAD_SIZE - 1))  ==
> +		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1)));
> +}
> +
> +/**
> + * regs_get_kernel_stack_nth() - get Nth entry of the stack
> + * @regs:	pt_regs which contains kernel stack pointer.
> + * @n:		stack entry number.
> + *
> + * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
> + * is specifined by @regs. If the @n th entry is NOT in the kernel stack,
> + * this returns 0.
> + */
> +static inline unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
> +						      unsigned n)
> +{
> +	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
> +	addr += n;
> +	if (regs_within_kernel_stack(regs, (unsigned long)addr))
> +		return *addr;
> +	else
> +		return 0;
> +}
> +
> +/**
> + * regs_get_argument_nth() - get Nth argument at function call
> + * @regs:	pt_regs which contains registers at function entry.
> + * @n:		argument number.
> + *
> + * regs_get_argument_nth() returns @n th argument of a function call.
> + * Since usually the kernel stack will be changed right after function entry,
> + * you must use this at function entry. If the @n th entry is NOT in the
> + * kernel stack or pt_regs, this returns 0.
> + */
> +#ifdef CONFIG_X86_32
> +#define NR_REGPARMS 3
> +static inline unsigned long regs_get_argument_nth(struct pt_regs *regs,
> +						  unsigned n)
> +{
> +	if (n < NR_REGPARMS) {
> +		switch (n) {
> +		case 0:
> +			return regs->ax;
> +		case 1:
> +			return regs->dx;
> +		case 2:
> +			return regs->cx;
> +		}
> +		return 0;
> +	} else {
> +		/*
> +		 * The typical case: arg n is on the stack.
> +		 * (Note: stack[0] = return address, so skip it)
> +		 */
> +		return regs_get_kernel_stack_nth(regs, 1 + n - NR_REGPARMS);
> +	}
> +}
> +#else /* CONFIG_X86_64 */
> +#define NR_REGPARMS 6
> +static inline unsigned long regs_get_argument_nth(struct pt_regs *regs,
> +						  unsigned n)
> +{
> +	if (n < NR_REGPARMS) {
> +		switch (n) {
> +		case 0:
> +			return regs->di;
> +		case 1:
> +			return regs->si;
> +		case 2:
> +			return regs->dx;
> +		case 3:
> +			return regs->cx;
> +		case 4:
> +			return regs->r8;
> +		case 5:
> +			return regs->r9;
> +		}
> +		return 0;
> +	} else {
> +		/*
> +		 * The typical case: arg n is on the stack.
> +		 * (Note: stack[0] = return address, so skip it)
> +		 */
> +		return regs_get_kernel_stack_nth(regs, 1 + n - NR_REGPARMS);
> +	}
> +}
> +#endif
> +
>  /*
>   * These are defined as per linux/ptrace.h, which see.
>   */
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> index b457f78..2944d3a 100644
> --- a/arch/x86/kernel/ptrace.c
> +++ b/arch/x86/kernel/ptrace.c
> @@ -49,6 +49,79 @@ enum x86_regset {
>  	REGSET_IOPERM32,
>  };
>  
> +struct pt_regs_offset {
> +	const char *name;
> +	int offset;
> +};
> +
> +#define REG_OFFSET_NAME(r) {.name = #r, .offset = offsetof(struct pt_regs, r)}
> +#define REG_OFFSET_END {.name = NULL, .offset = 0}
> +
> +static const struct pt_regs_offset regoffset_table[] = {
> +#ifdef CONFIG_X86_64
> +	REG_OFFSET_NAME(r15),
> +	REG_OFFSET_NAME(r14),
> +	REG_OFFSET_NAME(r13),
> +	REG_OFFSET_NAME(r12),
> +	REG_OFFSET_NAME(r11),
> +	REG_OFFSET_NAME(r10),
> +	REG_OFFSET_NAME(r9),
> +	REG_OFFSET_NAME(r8),
> +#endif
> +	REG_OFFSET_NAME(bx),
> +	REG_OFFSET_NAME(cx),
> +	REG_OFFSET_NAME(dx),
> +	REG_OFFSET_NAME(si),
> +	REG_OFFSET_NAME(di),
> +	REG_OFFSET_NAME(bp),
> +	REG_OFFSET_NAME(ax),
> +#ifdef CONFIG_X86_32
> +	REG_OFFSET_NAME(ds),
> +	REG_OFFSET_NAME(es),
> +	REG_OFFSET_NAME(fs),
> +	REG_OFFSET_NAME(gs),
> +#endif
> +	REG_OFFSET_NAME(orig_ax),
> +	REG_OFFSET_NAME(ip),
> +	REG_OFFSET_NAME(cs),
> +	REG_OFFSET_NAME(flags),
> +	REG_OFFSET_NAME(sp),
> +	REG_OFFSET_NAME(ss),
> +	REG_OFFSET_END,
> +};
> +
> +/**
> + * regs_query_register_offset() - query register offset from its name
> + * @name:	the name of a register
> + *
> + * regs_query_register_offset() returns the offset of a register in struct
> + * pt_regs from its name. If the name is invalid, this returns -EINVAL;
> + */
> +int regs_query_register_offset(const char *name)
> +{
> +	const struct pt_regs_offset *roff;
> +	for (roff = regoffset_table; roff->name != NULL; roff++)
> +		if (!strcmp(roff->name, name))
> +			return roff->offset;
> +	return -EINVAL;
> +}
> +
> +/**
> + * regs_query_register_name() - query register name from its offset
> + * @offset:	the offset of a register in struct pt_regs.
> + *
> + * regs_query_register_name() returns the name of a register from its
> + * offset in struct pt_regs. If the @offset is invalid, this returns NULL;
> + */
> +const char *regs_query_register_name(unsigned offset)
> +{
> +	const struct pt_regs_offset *roff;
> +	for (roff = regoffset_table; roff->name != NULL; roff++)
> +		if (roff->offset == offset)
> +			return roff->name;
> +	return NULL;
> +}
> +
>  /*
>   * does not yet catch signals sent when the child dies.
>   * in exit.c or in signal.c.
> 
> 
> -- 
> Masami Hiramatsu
> 
> Software Engineer
> Hitachi Computer Products (America), Inc.
> Software Solutions Division
> 
> e-mail: mhiramat@redhat.com