Re: [PATCH v2 3/5] powerpc: introduce a new helper to obtain function entry points

Masami Hiramatsu
2017-04-13T04:32:34Z

On Wed, 12 Apr 2017 16:28:26 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> kprobe_lookup_name() is specific to the kprobe subsystem and may not
> always return the function entry point (in a subsequent patch for
> KPROBES_ON_FTRACE).

If so, please move this patch into that series. It is hard to review
patches which requires for other series.

Thank you,

> For looking up function entry points, introduce a
> separate helper and use the same in optprobes.c
>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> arch/powerpc/include/asm/code-patching.h | 37 ++++++++++++++++++++++++++++++++
> arch/powerpc/kernel/optprobes.c | 6 +++---
> 2 files changed, 40 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
> index 8ab937771068..3e994f404434 100644
> --- a/arch/powerpc/include/asm/code-patching.h
> +++ b/arch/powerpc/include/asm/code-patching.h
> @@ -12,6 +12,8 @@
>
> #include <asm/types.h>
> #include <asm/ppc-opcode.h>
> +#include <linux/string.h>
> +#include <linux/kallsyms.h>
>
> /* Flags for create_branch:
> * "b" == create_branch(addr, target, 0);
> @@ -99,6 +101,41 @@ static inline unsigned long ppc_global_function_entry(void *func)
> #endif
> }
>
> +/*
> + * Wrapper around kallsyms_lookup() to return function entry address:
> + * - For ABIv1, we lookup the dot variant.
> + * - For ABIv2, we return the local entry point.
> + */
> +static inline unsigned long ppc_kallsyms_lookup_name(const char *name)
> +{
> + unsigned long addr;
> +#ifdef PPC64_ELF_ABI_v1
> + /* check for dot variant */
> + char dot_name[1 + KSYM_NAME_LEN];
> + bool dot_appended = false;
> + if (name[0] != '.') {
> + dot_name[0] = '.';
> + dot_name[1] = '\0';
> + strncat(dot_name, name, KSYM_NAME_LEN - 2);
> + dot_appended = true;
> + } else {
> + dot_name[0] = '\0';
> + strncat(dot_name, name, KSYM_NAME_LEN - 1);
> + }
> + addr = kallsyms_lookup_name(dot_name);
> + if (!addr && dot_appended)
> + /* Let's try the original non-dot symbol lookup */
> + addr = kallsyms_lookup_name(name);
> +#elif defined(PPC64_ELF_ABI_v2)
> + addr = kallsyms_lookup_name(name);
> + if (addr)
> + addr = ppc_function_entry((void *)addr);
> +#else
> + addr = kallsyms_lookup_name(name);
> +#endif
> + return addr;
> +}
> +
> #ifdef CONFIG_PPC64
> /*
> * Some instruction encodings commonly used in dynamic ftracing
> diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
> index ce81a322251c..ec60ed0d4aad 100644
> --- a/arch/powerpc/kernel/optprobes.c
> +++ b/arch/powerpc/kernel/optprobes.c
> @@ -243,10 +243,10 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
> /*
> * 2. branch to optimized_callback() and emulate_step()
> */
> - op_callback_addr = kprobe_lookup_name("optimized_callback", 0);
> - emulate_step_addr = kprobe_lookup_name("emulate_step", 0);
> + op_callback_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("optimized_callback");
> + emulate_step_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("emulate_step");
> if (!op_callback_addr || !emulate_step_addr) {
> - WARN(1, "kprobe_lookup_name() failed\n");
> + WARN(1, "Unable to lookup optimized_callback()/emulate_step()\n");
> goto error;
> }
>
> --
> 2.12.1
>

--
Masami Hiramatsu <mhiramat@kernel.org>