kernel: tracepoints: add support for relative references

To avoid the need for relocating absolute references to tracepoint
structures at boot time when running relocatable kernels (which may
take a disproportionate amount of space), add the option to emit
these tables as relative references instead.

Link: http://lkml.kernel.org/r/20180704083651.24360-7-ard.biesheuvel@linaro.org
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morris <james.morris@microsoft.com>
Cc: James Morris <jmorris@namei.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 26 insertions, 23 deletions

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 96db841bf0fc..bf2c06ef9afc 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -371,6 +371,27 @@ int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
 }
 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
 
+static void for_each_tracepoint_range(struct tracepoint * const *begin,
+		struct tracepoint * const *end,
+		void (*fct)(struct tracepoint *tp, void *priv),
+		void *priv)
+{
+	if (!begin)
+		return;
+
+	if (IS_ENABLED(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS)) {
+		const int *iter;
+
+		for (iter = (const int *)begin; iter < (const int *)end; iter++)
+			fct(offset_to_ptr(iter), priv);
+	} else {
+		struct tracepoint * const *iter;
+
+		for (iter = begin; iter < end; iter++)
+			fct(*iter, priv);
+	}
+}
+
 #ifdef CONFIG_MODULES
 bool trace_module_has_bad_taint(struct module *mod)
 {
@@ -435,15 +456,9 @@ EXPORT_SYMBOL_GPL(unregister_tracepoint_module_notifier);
  * Ensure the tracer unregistered the module's probes before the module
  * teardown is performed. Prevents leaks of probe and data pointers.
  */
-static void tp_module_going_check_quiescent(struct tracepoint * const *begin,
-		struct tracepoint * const *end)
+static void tp_module_going_check_quiescent(struct tracepoint *tp, void *priv)
 {
-	struct tracepoint * const *iter;
-
-	if (!begin)
-		return;
-	for (iter = begin; iter < end; iter++)
-		WARN_ON_ONCE((*iter)->funcs);
+	WARN_ON_ONCE(tp->funcs);
 }
 
 static int tracepoint_module_coming(struct module *mod)
@@ -494,8 +509,9 @@ static void tracepoint_module_going(struct module *mod)
 			 * Called the going notifier before checking for
 			 * quiescence.
 			 */
-			tp_module_going_check_quiescent(mod->tracepoints_ptrs,
-				mod->tracepoints_ptrs + mod->num_tracepoints);
+			for_each_tracepoint_range(mod->tracepoints_ptrs,
+				mod->tracepoints_ptrs + mod->num_tracepoints,
+				tp_module_going_check_quiescent, NULL);
 			break;
 		}
 	}
@@ -547,19 +563,6 @@ static __init int init_tracepoints(void)
 __initcall(init_tracepoints);
 #endif /* CONFIG_MODULES */
 
-static void for_each_tracepoint_range(struct tracepoint * const *begin,
-		struct tracepoint * const *end,
-		void (*fct)(struct tracepoint *tp, void *priv),
-		void *priv)
-{
-	struct tracepoint * const *iter;
-
-	if (!begin)
-		return;
-	for (iter = begin; iter < end; iter++)
-		fct(*iter, priv);
-}
-
 /**
  * for_each_kernel_tracepoint - iteration on all kernel tracepoints
  * @fct: callback