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Subject[PATCH v6 5/8] kernel: tracepoints: add support for relative references
Date
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.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
include/linux/tracepoint.h | 19 ++++++--
kernel/tracepoint.c | 50 +++++++++++---------
2 files changed, 42 insertions(+), 27 deletions(-)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index a26ffbe09e71..d02bf1a695e8 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -228,6 +228,19 @@ extern void syscall_unregfunc(void);
return static_key_false(&__tracepoint_##name.key); \
}

+#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
+#define __TRACEPOINT_ENTRY(name) \
+ asm(" .section \"__tracepoints_ptrs\", \"a\" \n" \
+ " .balign 4 \n" \
+ " .long " VMLINUX_SYMBOL_STR(__tracepoint_##name) " - .\n" \
+ " .previous \n")
+#else
+#define __TRACEPOINT_ENTRY(name) \
+ static struct tracepoint * const __tracepoint_ptr_##name __used \
+ __attribute__((section("__tracepoints_ptrs"))) = \
+ &__tracepoint_##name
+#endif
+
/*
* We have no guarantee that gcc and the linker won't up-align the tracepoint
* structures, so we create an array of pointers that will be used for iteration
@@ -237,11 +250,9 @@ extern void syscall_unregfunc(void);
static const char __tpstrtab_##name[] \
__attribute__((section("__tracepoints_strings"))) = #name; \
struct tracepoint __tracepoint_##name \
- __attribute__((section("__tracepoints"))) = \
+ __attribute__((section("__tracepoints"), used)) = \
{ __tpstrtab_##name, STATIC_KEY_INIT_FALSE, reg, unreg, NULL };\
- static struct tracepoint * const __tracepoint_ptr_##name __used \
- __attribute__((section("__tracepoints_ptrs"))) = \
- &__tracepoint_##name;
+ __TRACEPOINT_ENTRY(name);

#define DEFINE_TRACE(name) \
DEFINE_TRACE_FN(name, NULL, NULL);
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 685c50ae6300..05649fef106c 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -327,6 +327,28 @@ 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((struct tracepoint *)((unsigned long)iter + *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)
{
@@ -391,15 +413,9 @@ 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)
@@ -450,8 +466,9 @@ 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;
}
}
@@ -503,19 +520,6 @@ 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
--
2.11.0
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