From: Steven Rostedt Currently the trace_event structures are placed in the _ftrace_events section, and at link time, the linker makes one large array of all the trace_event structures. On boot up, this array is read (much like the initcall sections) and the events are processed. The problem is that there is no guarantee that gcc will place complex structures nicely together in an array format. Two structures in the same file may be placed awkwardly, because gcc has no clue that they are suppose to be in an array. A hack was used previous to force the alignment to 4, to pack the structures together. But this caused alignment issues with other architectures (sparc). Instead of packing the structures into an array, the structures' addresses are now put into the _ftrace_event section. As pointers are always the natural alignment, gcc should always pack them tightly together (otherwise initcall, extable, etc would also fail). By having the pointers to the structures in the section, we can still iterate the trace_events without causing unnecessary alignment problems with other architectures, or depending on the current behaviour of gcc that will likely change in the future just to tick us kernel developers off a little more. The _ftrace_event section is also moved into the .init.data section as it is now only needed at boot up. Suggested-by: David Miller Cc: Mathieu Desnoyers Acked-by: David S. Miller Signed-off-by: Steven Rostedt --- include/asm-generic/vmlinux.lds.h | 7 +++---- include/linux/module.h | 2 +- include/linux/syscalls.h | 10 ++++++---- include/trace/ftrace.h | 24 +++++++++++++----------- kernel/trace/trace_events.c | 12 ++++++------ kernel/trace/trace_export.c | 6 +++--- 6 files changed, 32 insertions(+), 29 deletions(-) diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 6ebb810..f53708b 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -124,7 +124,8 @@ #endif #ifdef CONFIG_EVENT_TRACING -#define FTRACE_EVENTS() VMLINUX_SYMBOL(__start_ftrace_events) = .; \ +#define FTRACE_EVENTS() . = ALIGN(8); \ + VMLINUX_SYMBOL(__start_ftrace_events) = .; \ *(_ftrace_events) \ VMLINUX_SYMBOL(__stop_ftrace_events) = .; #else @@ -179,9 +180,6 @@ TRACE_PRINTKS() \ \ STRUCT_ALIGN(); \ - FTRACE_EVENTS() \ - \ - STRUCT_ALIGN(); \ TRACE_SYSCALLS() /* @@ -482,6 +480,7 @@ KERNEL_CTORS() \ *(.init.rodata) \ MCOUNT_REC() \ + FTRACE_EVENTS() \ DEV_DISCARD(init.rodata) \ CPU_DISCARD(init.rodata) \ MEM_DISCARD(init.rodata) \ diff --git a/include/linux/module.h b/include/linux/module.h index e7c6385..7695a30 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -389,7 +389,7 @@ struct module unsigned int num_trace_bprintk_fmt; #endif #ifdef CONFIG_EVENT_TRACING - struct ftrace_event_call *trace_events; + struct ftrace_event_call **trace_events; unsigned int num_trace_events; #endif #ifdef CONFIG_FTRACE_MCOUNT_RECORD diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 18cd068..45508fe 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -128,28 +128,30 @@ extern struct trace_event_functions exit_syscall_print_funcs; static struct syscall_metadata \ __attribute__((__aligned__(4))) __syscall_meta_##sname; \ static struct ftrace_event_call __used \ - __attribute__((__aligned__(4))) \ - __attribute__((section("_ftrace_events"))) \ event_enter_##sname = { \ .name = "sys_enter"#sname, \ .class = &event_class_syscall_enter, \ .event.funcs = &enter_syscall_print_funcs, \ .data = (void *)&__syscall_meta_##sname,\ }; \ + static struct ftrace_event_call __used \ + __attribute__((section("_ftrace_events"))) \ + *__event_enter_##sname = &event_enter_##sname; \ __TRACE_EVENT_FLAGS(enter_##sname, TRACE_EVENT_FL_CAP_ANY) #define SYSCALL_TRACE_EXIT_EVENT(sname) \ static struct syscall_metadata \ __attribute__((__aligned__(4))) __syscall_meta_##sname; \ static struct ftrace_event_call __used \ - __attribute__((__aligned__(4))) \ - __attribute__((section("_ftrace_events"))) \ event_exit_##sname = { \ .name = "sys_exit"#sname, \ .class = &event_class_syscall_exit, \ .event.funcs = &exit_syscall_print_funcs, \ .data = (void *)&__syscall_meta_##sname,\ }; \ + static struct ftrace_event_call __used \ + __attribute__((section("_ftrace_events"))) \ + *__event_exit_##sname = &event_exit_##sname; \ __TRACE_EVENT_FLAGS(exit_##sname, TRACE_EVENT_FL_CAP_ANY) #define SYSCALL_METADATA(sname, nb) \ diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h index e16610c..3e68366 100644 --- a/include/trace/ftrace.h +++ b/include/trace/ftrace.h @@ -446,14 +446,16 @@ static inline notrace int ftrace_get_offsets_##call( \ * .reg = ftrace_event_reg, * }; * - * static struct ftrace_event_call __used - * __attribute__((__aligned__(4))) - * __attribute__((section("_ftrace_events"))) event_ = { + * static struct ftrace_event_call event_ = { * .name = "", * .class = event_class_