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    Subject[PATCH 4/7] ftrace, PPC: use probe_kernel API to modify code
    Impact: use cleaner probe_kernel API over assembly

    Using probe_kernel_read/write interface is a much cleaner approach
    than the current assembly version.

    Signed-off-by: Steven Rostedt <srostedt@redhat.com>
    ---
    arch/powerpc/kernel/ftrace.c | 53 ++++++++++++++++-------------------------
    1 files changed, 21 insertions(+), 32 deletions(-)

    diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
    index aa5d0b2..3852919 100644
    --- a/arch/powerpc/kernel/ftrace.c
    +++ b/arch/powerpc/kernel/ftrace.c
    @@ -9,6 +9,7 @@

    #include <linux/spinlock.h>
    #include <linux/hardirq.h>
    +#include <linux/uaccess.h>
    #include <linux/ftrace.h>
    #include <linux/percpu.h>
    #include <linux/init.h>
    @@ -72,45 +73,33 @@ static int
    ftrace_modify_code(unsigned long ip, unsigned char *old_code,
    unsigned char *new_code)
    {
    - unsigned replaced;
    - unsigned old = *(unsigned *)old_code;
    - unsigned new = *(unsigned *)new_code;
    - int faulted = 0;
    + unsigned char replaced[MCOUNT_INSN_SIZE];

    /*
    * Note: Due to modules and __init, code can
    * disappear and change, we need to protect against faulting
    - * as well as code changing.
    + * as well as code changing. We do this by using the
    + * probe_kernel_* functions.
    *
    * No real locking needed, this code is run through
    - * kstop_machine.
    + * kstop_machine, or before SMP starts.
    */
    - asm volatile (
    - "1: lwz %1, 0(%2)\n"
    - " cmpw %1, %5\n"
    - " bne 2f\n"
    - " stwu %3, 0(%2)\n"
    - "2:\n"
    - ".section .fixup, \"ax\"\n"
    - "3: li %0, 1\n"
    - " b 2b\n"
    - ".previous\n"
    - ".section __ex_table,\"a\"\n"
    - _ASM_ALIGN "\n"
    - _ASM_PTR "1b, 3b\n"
    - ".previous"
    - : "=r"(faulted), "=r"(replaced)
    - : "r"(ip), "r"(new),
    - "0"(faulted), "r"(old)
    - : "memory");
    -
    - if (replaced != old && replaced != new)
    - faulted = 2;
    -
    - if (!faulted)
    - flush_icache_range(ip, ip + 8);
    -
    - return faulted;
    +
    + /* read the text we want to modify */
    + if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
    + return -EFAULT;
    +
    + /* Make sure it is what we expect it to be */
    + if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
    + return -EINVAL;
    +
    + /* replace the text with the new text */
    + if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
    + return -EPERM;
    +
    + flush_icache_range(ip, ip + 8);
    +
    + return 0;
    }

    static int test_24bit_addr(unsigned long ip, unsigned long addr)
    --
    1.5.6.5
    --


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