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    Subject[PATCH -tip -v10 5/7] x86: add pt_regs register and stack access APIs
    Andi Kleen wrote:
    > On Mon, Jul 06, 2009 at 03:28:02PM -0400, Masami Hiramatsu wrote:
    >> I'm not so sure about your idea.
    >> Would you mean below code?
    >>
    >> int offs_table[NR_REGPARMS] = {
    >
    > not REGPARMS of course
    >
    >> [0] = offsetof(struct pt_regs, di),
    >> ...
    >> };
    >> if (n < NR_REGPARMS)
    >> return *((unsigned long *)regs + offs_table[n]);
    >
    > Yes.

    OK, here, I updated my patch.

    Thank you,


    x86: add pt_regs register and stack access APIs

    From: Masami Hiramatsu <mhiramat@redhat.com>

    Add following APIs for accessing registers and stack entries from pt_regs.
    These APIs are required by kprobes-based event tracer on ftrace.
    Some other debugging tools might be able to use it too.

    - 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 v10:
    - Use an offsetof table in regs_get_argument_nth().

    Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
    Cc: Andi Kleen <andi@firstfloor.org>
    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
    ---

    arch/x86/include/asm/ptrace.h | 61 ++++++++++++++++++++++
    arch/x86/kernel/ptrace.c | 112 +++++++++++++++++++++++++++++++++++++++++
    2 files changed, 173 insertions(+), 0 deletions(-)


    diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
    index 0f0d908..a9b7e2d 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 +217,66 @@ 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;
    +}
    +
    +/* Get Nth argument at function call */
    +extern unsigned long regs_get_argument_nth(struct pt_regs *regs, unsigned n);
    +
    /*
    * 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 cabdabc..4f9b513 100644
    --- a/arch/x86/kernel/ptrace.c
    +++ b/arch/x86/kernel/ptrace.c
    @@ -49,6 +49,118 @@ 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;
    +}
    +
    +static const int arg_offs_table[] = {
    +#ifdef CONFIG_X86_32
    + [0] = offsetof(struct pt_regs, ax),
    + [1] = offsetof(struct pt_regs, dx),
    + [2] = offsetof(struct pt_regs, cx)
    +#else /* CONFIG_X86_64 */
    + [0] = offsetof(struct pt_regs, di),
    + [1] = offsetof(struct pt_regs, si),
    + [2] = offsetof(struct pt_regs, dx),
    + [3] = offsetof(struct pt_regs, cx),
    + [4] = offsetof(struct pt_regs, r8),
    + [5] = offsetof(struct pt_regs, r9)
    +#endif
    +};
    +
    +/**
    + * 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.
    + */
    +unsigned long regs_get_argument_nth(struct pt_regs *regs, unsigned n)
    +{
    + if (n < ARRAY_SIZE(arg_offs_table))
    + return *((unsigned long *)regs + arg_offs_table[n]);
    + else {
    + /*
    + * The typical case: arg n is on the stack.
    + * (Note: stack[0] = return address, so skip it)
    + */
    + n -= ARRAY_SIZE(arg_offs_table);
    + return regs_get_kernel_stack_nth(regs, 1 + n);
    + }
    +}
    +
    /*
    * 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



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