ftrace: Add ftrace_lookup_symbols function

Adding ftrace_lookup_symbols function that resolves array of symbols
with single pass over kallsyms.

The user provides array of string pointers with count and pointer to
allocated array for resolved values.

  int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt,
                            unsigned long *addrs)

It iterates all kallsyms symbols and tries to loop up each in provided
symbols array with bsearch. The symbols array needs to be sorted by
name for this reason.

We also check each symbol to pass ftrace_location, because this API
will be used for fprobe symbols resolving.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20220510122616.2652285-3-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 4816b7e110472c06063dec6d67cac1c5419e2a6b..820500430eae0dd6ec1a7400f5fd668c65c1d12f 100644 (file)
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -303,6 +303,8 @@ int unregister_ftrace_function(struct ftrace_ops *ops);
 extern void ftrace_stub(unsigned long a0, unsigned long a1,
                        struct ftrace_ops *op, struct ftrace_regs *fregs);
 
+
+int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs);
 #else /* !CONFIG_FUNCTION_TRACER */
 /*
  * (un)register_ftrace_function must be a macro since the ops parameter
@@ -313,6 +315,10 @@ extern void ftrace_stub(unsigned long a0, unsigned long a1,
 static inline void ftrace_kill(void) { }
 static inline void ftrace_free_init_mem(void) { }
 static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { }
+static inline int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs)
+{
+       return -EOPNOTSUPP;
+}
 #endif /* CONFIG_FUNCTION_TRACER */
 
 struct ftrace_func_entry {

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index fdfd308bebc48696da2f66ada1e398929bdc8ee9..fbdf8d3279aca3763fce18305ca5ff4af730c005 100644 (file)
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -29,6 +29,7 @@
 #include <linux/compiler.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
+#include <linux/bsearch.h>
 
 /*
  * These will be re-linked against their real values

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4f1d2f5e7263412f5c5467fef32621e05cb14450..07d87c7a525d14a751fc049e57dd9417e253a373 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7964,3 +7964,65 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
        mutex_unlock(&ftrace_lock);
        return ret;
 }
+
+static int symbols_cmp(const void *a, const void *b)
+{
+       const char **str_a = (const char **) a;
+       const char **str_b = (const char **) b;
+
+       return strcmp(*str_a, *str_b);
+}
+
+struct kallsyms_data {
+       unsigned long *addrs;
+       const char **syms;
+       size_t cnt;
+       size_t found;
+};
+
+static int kallsyms_callback(void *data, const char *name,
+                            struct module *mod, unsigned long addr)
+{
+       struct kallsyms_data *args = data;
+
+       if (!bsearch(&name, args->syms, args->cnt, sizeof(*args->syms), symbols_cmp))
+               return 0;
+
+       addr = ftrace_location(addr);
+       if (!addr)
+               return 0;
+
+       args->addrs[args->found++] = addr;
+       return args->found == args->cnt ? 1 : 0;
+}
+
+/**
+ * ftrace_lookup_symbols - Lookup addresses for array of symbols
+ *
+ * @sorted_syms: array of symbols pointers symbols to resolve,
+ * must be alphabetically sorted
+ * @cnt: number of symbols/addresses in @syms/@addrs arrays
+ * @addrs: array for storing resulting addresses
+ *
+ * This function looks up addresses for array of symbols provided in
+ * @syms array (must be alphabetically sorted) and stores them in
+ * @addrs array, which needs to be big enough to store at least @cnt
+ * addresses.
+ *
+ * This function returns 0 if all provided symbols are found,
+ * -ESRCH otherwise.
+ */
+int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs)
+{
+       struct kallsyms_data args;
+       int err;
+
+       args.addrs = addrs;
+       args.syms = sorted_syms;
+       args.cnt = cnt;
+       args.found = 0;
+       err = kallsyms_on_each_symbol(kallsyms_callback, &args);
+       if (err < 0)
+               return err;
+       return args.found == args.cnt ? 0 : -ESRCH;
+}