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

Naveen N. Rao
2017-04-12T11:00:52Z

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). 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