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tracepoints: Fix section alignment using pointer array 

Make the tracepoints more robust, making them solid enough to handle compiler
changes by not relying on anything based on compiler-specific behavior with
respect to structure alignment. Implement an approach proposed by David Miller:
use an array of const pointers to refer to the individual structures, and export
this pointer array through the linker script rather than the structures per se.
It will consume 32 extra bytes per tracepoint (24 for structure padding and 8
for the pointers), but are less likely to break due to compiler changes.

History:

commit 7e066fb8 tracepoints: add DECLARE_TRACE() and DEFINE_TRACE()
added the aligned(32) type and variable attribute to the tracepoint structures
to deal with gcc happily aligning statically defined structures on 32-byte
multiples.

One attempt was to use a 8-byte alignment for tracepoint structures by applying
both the variable and type attribute to tracepoint structures definitions and
declarations. It worked fine with gcc 4.5.1, but broke with gcc 4.4.4 and 4.4.5.

The reason is that the "aligned" attribute only specify the _minimum_ alignment
for a structure, leaving both the compiler and the linker free to align on
larger multiples. Because tracepoint.c expects the structures to be placed as an
array within each section, up-alignment cause NULL-pointer exceptions due to the
extra unexpected padding.

(this patch applies on top of -tip)

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: David S. Miller <davem@davemloft.net>
LKML-Reference: <20110126222622.GA10794@Krystal>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Ingo Molnar <mingo@elte.hu>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Mathieu Desnoyers 2011-01-26 17:26:22 -05:00 committed by Steven Rostedt
parent e4a9ea5ee7
commit 6549864629
5 changed files with 50 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/asm-generic/vmlinux.lds.h
View File

@ -166,10 +166,8 @@
CPU_KEEP(exit.data) \
MEM_KEEP(init.data) \
MEM_KEEP(exit.data) \
. = ALIGN(32); \
VMLINUX_SYMBOL(__start___tracepoints) = .; \
STRUCT_ALIGN(); \
*(__tracepoints) \
VMLINUX_SYMBOL(__stop___tracepoints) = .; \
/* implement dynamic printk debug */ \
. = ALIGN(8); \
VMLINUX_SYMBOL(__start___verbose) = .; \
@ -218,6 +216,10 @@
VMLINUX_SYMBOL(__start_rodata) = .; \
*(.rodata) *(.rodata.*) \
*(__vermagic) /* Kernel version magic */ \
. = ALIGN(8); \
VMLINUX_SYMBOL(__start___tracepoints_ptrs) = .; \
*(__tracepoints_ptrs) /* Tracepoints: pointer array */\
VMLINUX_SYMBOL(__stop___tracepoints_ptrs) = .; \
*(__markers_strings) /* Markers: strings */ \
*(__tracepoints_strings)/* Tracepoints: strings */ \
} \

2
include/linux/module.h
View File

@ -377,7 +377,7 @@ struct module
keeping pointers to this stuff */
char *args;
#ifdef CONFIG_TRACEPOINTS
struct tracepoint *tracepoints;
struct tracepoint * const *tracepoints_ptrs;
unsigned int num_tracepoints;
#endif
#ifdef HAVE_JUMP_LABEL

35
include/linux/tracepoint.h
View File

@ -33,12 +33,7 @@ struct tracepoint {
void (*regfunc)(void);
void (*unregfunc)(void);
struct tracepoint_func __rcu *funcs;
} __attribute__((aligned(32))); /*
* Aligned on 32 bytes because it is
* globally visible and gcc happily
* align these on the structure size.
* Keep in sync with vmlinux.lds.h.
*/
};
/*
* Connect a probe to a tracepoint.
@ -61,15 +56,15 @@ extern void tracepoint_probe_update_all(void);
struct tracepoint_iter {
struct module *module;
struct tracepoint *tracepoint;
struct tracepoint * const *tracepoint;
};
extern void tracepoint_iter_start(struct tracepoint_iter *iter);
extern void tracepoint_iter_next(struct tracepoint_iter *iter);
extern void tracepoint_iter_stop(struct tracepoint_iter *iter);
extern void tracepoint_iter_reset(struct tracepoint_iter *iter);
extern int tracepoint_get_iter_range(struct tracepoint **tracepoint,
struct tracepoint *begin, struct tracepoint *end);
extern int tracepoint_get_iter_range(struct tracepoint * const **tracepoint,
struct tracepoint * const *begin, struct tracepoint * const *end);
/*
* tracepoint_synchronize_unregister must be called between the last tracepoint
@ -84,11 +79,13 @@ static inline void tracepoint_synchronize_unregister(void)
#define PARAMS(args...) args
#ifdef CONFIG_TRACEPOINTS
extern void tracepoint_update_probe_range(struct tracepoint *begin,
struct tracepoint *end);
extern
void tracepoint_update_probe_range(struct tracepoint * const *begin,
struct tracepoint * const *end);
#else
static inline void tracepoint_update_probe_range(struct tracepoint *begin,
struct tracepoint *end)
static inline
void tracepoint_update_probe_range(struct tracepoint * const *begin,
struct tracepoint * const *end)
{ }
#endif /* CONFIG_TRACEPOINTS */
@ -174,12 +171,20 @@ do_trace: \
{ \
}
/*
* 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
* on the tracepoints.
*/
#define DEFINE_TRACE_FN(name, reg, unreg) \
static const char __tpstrtab_##name[] \
__attribute__((section("__tracepoints_strings"))) = #name; \
struct tracepoint __tracepoint_##name \
__attribute__((section("__tracepoints"), aligned(32))) = \
{ __tpstrtab_##name, 0, reg, unreg, NULL }
__attribute__((section("__tracepoints"))) = \
{ __tpstrtab_##name, 0, reg, unreg, NULL }; \
static struct tracepoint * const __tracepoint_ptr_##name __used \
__attribute__((section("__tracepoints_ptrs"))) = \
&__tracepoint_##name;
#define DEFINE_TRACE(name) \
DEFINE_TRACE_FN(name, NULL, NULL);

16
kernel/module.c
View File

@ -2460,9 +2460,9 @@ static void find_module_sections(struct module *mod, struct load_info *info)
#endif
#ifdef CONFIG_TRACEPOINTS
mod->tracepoints = section_objs(info, "__tracepoints",
sizeof(*mod->tracepoints),
&mod->num_tracepoints);
mod->tracepoints_ptrs = section_objs(info, "__tracepoints_ptrs",
sizeof(*mod->tracepoints_ptrs),
&mod->num_tracepoints);
#endif
#ifdef HAVE_JUMP_LABEL
mod->jump_entries = section_objs(info, "__jump_table",
@ -3393,7 +3393,7 @@ void module_layout(struct module *mod,
struct modversion_info *ver,
struct kernel_param *kp,
struct kernel_symbol *ks,
struct tracepoint *tp)
struct tracepoint * const *tp)
{
}
EXPORT_SYMBOL(module_layout);
@ -3407,8 +3407,8 @@ void module_update_tracepoints(void)
mutex_lock(&module_mutex);
list_for_each_entry(mod, &modules, list)
if (!mod->taints)
tracepoint_update_probe_range(mod->tracepoints,
mod->tracepoints + mod->num_tracepoints);
tracepoint_update_probe_range(mod->tracepoints_ptrs,
mod->tracepoints_ptrs + mod->num_tracepoints);
mutex_unlock(&module_mutex);
}
@ -3432,8 +3432,8 @@ int module_get_iter_tracepoints(struct tracepoint_iter *iter)
else if (iter_mod > iter->module)
iter->tracepoint = NULL;
found = tracepoint_get_iter_range(&iter->tracepoint,
iter_mod->tracepoints,
iter_mod->tracepoints
iter_mod->tracepoints_ptrs,
iter_mod->tracepoints_ptrs
+ iter_mod->num_tracepoints);
if (found) {
iter->module = iter_mod;

31
kernel/tracepoint.c
View File

@ -27,8 +27,8 @@
#include <linux/sched.h>
#include <linux/jump_label.h>
extern struct tracepoint __start___tracepoints[];
extern struct tracepoint __stop___tracepoints[];
extern struct tracepoint * const __start___tracepoints_ptrs[];
extern struct tracepoint * const __stop___tracepoints_ptrs[];
/* Set to 1 to enable tracepoint debug output */
static const int tracepoint_debug;
@ -298,10 +298,10 @@ static void disable_tracepoint(struct tracepoint *elem)
*
* Updates the probe callback corresponding to a range of tracepoints.
*/
void
tracepoint_update_probe_range(struct tracepoint *begin, struct tracepoint *end)
void tracepoint_update_probe_range(struct tracepoint * const *begin,
struct tracepoint * const *end)
{
struct tracepoint *iter;
struct tracepoint * const *iter;
struct tracepoint_entry *mark_entry;
if (!begin)
@ -309,12 +309,12 @@ tracepoint_update_probe_range(struct tracepoint *begin, struct tracepoint *end)
mutex_lock(&tracepoints_mutex);
for (iter = begin; iter < end; iter++) {
mark_entry = get_tracepoint(iter->name);
mark_entry = get_tracepoint((*iter)->name);
if (mark_entry) {
set_tracepoint(&mark_entry, iter,
set_tracepoint(&mark_entry, *iter,
!!mark_entry->refcount);
} else {
disable_tracepoint(iter);
disable_tracepoint(*iter);
}
}
mutex_unlock(&tracepoints_mutex);
@ -326,8 +326,8 @@ tracepoint_update_probe_range(struct tracepoint *begin, struct tracepoint *end)
static void tracepoint_update_probes(void)
{
/* Core kernel tracepoints */
tracepoint_update_probe_range(__start___tracepoints,
__stop___tracepoints);
tracepoint_update_probe_range(__start___tracepoints_ptrs,
__stop___tracepoints_ptrs);
/* tracepoints in modules. */
module_update_tracepoints();
}
@ -514,8 +514,8 @@ EXPORT_SYMBOL_GPL(tracepoint_probe_update_all);
* Will return the first tracepoint in the range if the input tracepoint is
* NULL.
*/
int tracepoint_get_iter_range(struct tracepoint **tracepoint,
struct tracepoint *begin, struct tracepoint *end)
int tracepoint_get_iter_range(struct tracepoint * const **tracepoint,
struct tracepoint * const *begin, struct tracepoint * const *end)
{
if (!*tracepoint && begin != end) {
*tracepoint = begin;
@ -534,7 +534,8 @@ static void tracepoint_get_iter(struct tracepoint_iter *iter)
/* Core kernel tracepoints */
if (!iter->module) {
found = tracepoint_get_iter_range(&iter->tracepoint,
__start___tracepoints, __stop___tracepoints);
__start___tracepoints_ptrs,
__stop___tracepoints_ptrs);
if (found)
goto end;
}
@ -585,8 +586,8 @@ int tracepoint_module_notify(struct notifier_block *self,
switch (val) {
case MODULE_STATE_COMING:
case MODULE_STATE_GOING:
tracepoint_update_probe_range(mod->tracepoints,
mod->tracepoints + mod->num_tracepoints);
tracepoint_update_probe_range(mod->tracepoints_ptrs,
mod->tracepoints_ptrs + mod->num_tracepoints);
break;
}
return 0;