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authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>2011-01-26 17:26:22 -0500
committerSteven Rostedt <rostedt@goodmis.org>2011-02-03 09:28:46 -0500
commit654986462939cd7ec18f276c6379a334dac106a7 (patch)
treeb9c70944012c24fa6d7cc973fa9b4b6e875ca842 /include/linux/tracepoint.h
parente4a9ea5ee7c8812a7bf0c3fb725ceeaa3d4c2fcc (diff)
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>
Diffstat (limited to 'include/linux/tracepoint.h')
-rw-r--r--include/linux/tracepoint.h35
1 files changed, 20 insertions, 15 deletions
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index c6814616653b..97c84a58efb8 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -33,12 +33,7 @@ struct tracepoint {
33 void (*regfunc)(void); 33 void (*regfunc)(void);
34 void (*unregfunc)(void); 34 void (*unregfunc)(void);
35 struct tracepoint_func __rcu *funcs; 35 struct tracepoint_func __rcu *funcs;
36} __attribute__((aligned(32))); /* 36};
37 * Aligned on 32 bytes because it is
38 * globally visible and gcc happily
39 * align these on the structure size.
40 * Keep in sync with vmlinux.lds.h.
41 */
42 37
43/* 38/*
44 * Connect a probe to a tracepoint. 39 * Connect a probe to a tracepoint.
@@ -61,15 +56,15 @@ extern void tracepoint_probe_update_all(void);
61 56
62struct tracepoint_iter { 57struct tracepoint_iter {
63 struct module *module; 58 struct module *module;
64 struct tracepoint *tracepoint; 59 struct tracepoint * const *tracepoint;
65}; 60};
66 61
67extern void tracepoint_iter_start(struct tracepoint_iter *iter); 62extern void tracepoint_iter_start(struct tracepoint_iter *iter);
68extern void tracepoint_iter_next(struct tracepoint_iter *iter); 63extern void tracepoint_iter_next(struct tracepoint_iter *iter);
69extern void tracepoint_iter_stop(struct tracepoint_iter *iter); 64extern void tracepoint_iter_stop(struct tracepoint_iter *iter);
70extern void tracepoint_iter_reset(struct tracepoint_iter *iter); 65extern void tracepoint_iter_reset(struct tracepoint_iter *iter);
71extern int tracepoint_get_iter_range(struct tracepoint **tracepoint, 66extern int tracepoint_get_iter_range(struct tracepoint * const **tracepoint,
72 struct tracepoint *begin, struct tracepoint *end); 67 struct tracepoint * const *begin, struct tracepoint * const *end);
73 68
74/* 69/*
75 * tracepoint_synchronize_unregister must be called between the last tracepoint 70 * tracepoint_synchronize_unregister must be called between the last tracepoint
@@ -84,11 +79,13 @@ static inline void tracepoint_synchronize_unregister(void)
84#define PARAMS(args...) args 79#define PARAMS(args...) args
85 80
86#ifdef CONFIG_TRACEPOINTS 81#ifdef CONFIG_TRACEPOINTS
87extern void tracepoint_update_probe_range(struct tracepoint *begin, 82extern
88 struct tracepoint *end); 83void tracepoint_update_probe_range(struct tracepoint * const *begin,
84 struct tracepoint * const *end);
89#else 85#else
90static inline void tracepoint_update_probe_range(struct tracepoint *begin, 86static inline
91 struct tracepoint *end) 87void tracepoint_update_probe_range(struct tracepoint * const *begin,
88 struct tracepoint * const *end)
92{ } 89{ }
93#endif /* CONFIG_TRACEPOINTS */ 90#endif /* CONFIG_TRACEPOINTS */
94 91
@@ -174,12 +171,20 @@ do_trace: \
174 { \ 171 { \
175 } 172 }
176 173
174/*
175 * We have no guarantee that gcc and the linker won't up-align the tracepoint
176 * structures, so we create an array of pointers that will be used for iteration
177 * on the tracepoints.
178 */
177#define DEFINE_TRACE_FN(name, reg, unreg) \ 179#define DEFINE_TRACE_FN(name, reg, unreg) \
178 static const char __tpstrtab_##name[] \ 180 static const char __tpstrtab_##name[] \
179 __attribute__((section("__tracepoints_strings"))) = #name; \ 181 __attribute__((section("__tracepoints_strings"))) = #name; \
180 struct tracepoint __tracepoint_##name \ 182 struct tracepoint __tracepoint_##name \
181 __attribute__((section("__tracepoints"), aligned(32))) = \ 183 __attribute__((section("__tracepoints"))) = \
182 { __tpstrtab_##name, 0, reg, unreg, NULL } 184 { __tpstrtab_##name, 0, reg, unreg, NULL }; \
185 static struct tracepoint * const __tracepoint_ptr_##name __used \
186 __attribute__((section("__tracepoints_ptrs"))) = \
187 &__tracepoint_##name;
183 188
184#define DEFINE_TRACE(name) \ 189#define DEFINE_TRACE(name) \
185 DEFINE_TRACE_FN(name, NULL, NULL); 190 DEFINE_TRACE_FN(name, NULL, NULL);