On Mon, 14 Aug 2017 11:52:31 +0100
Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
> include/linux/tracepoint.h | 19 +++++++++++++++----
> kernel/tracepoint.c | 19 ++++++++++++++-----
> 2 files changed, 29 insertions(+), 9 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..1c6689603764 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -28,8 +28,8 @@
> #include <linux/sched/task.h>
> #include <linux/static_key.h>
>
> -extern struct tracepoint * const __start___tracepoints_ptrs[];
> -extern struct tracepoint * const __stop___tracepoints_ptrs[];
> +extern const unsigned char __start___tracepoints_ptrs[];
> +extern const unsigned char __stop___tracepoints_ptrs[];
Does this have to be converted to a char array?
>
> /* Set to 1 to enable tracepoint debug output */
> static const int tracepoint_debug;
> @@ -503,17 +503,26 @@ 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,
> +static void for_each_tracepoint_range(const void *begin, const void *end,
> void (*fct)(struct tracepoint *tp, void *priv),
> void *priv)
> {
> +#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
> + const signed int *iter;
> +
> + if (!begin)
> + return;
> + for (iter = begin; iter < (signed int *)end; iter++) {
Isn't the typecasts here sufficient, even if the above end is defined
as a tracepoint * const *?
-- Steve
> + fct((struct tracepoint *)((unsigned long)iter + *iter), priv);
> + }
> +#else
> struct tracepoint * const *iter;
>
> if (!begin)
> return;
> - for (iter = begin; iter < end; iter++)
> + for (iter = begin; iter < (struct tracepoint * const *)end; iter++)
> fct(*iter, priv);
> +#endif
> }
>
> /**
