path: root/kernel
diff options
authorSteven Rostedt <srostedt@redhat.com>2011-02-02 17:06:09 -0500
committerSteven Rostedt <rostedt@goodmis.org>2011-02-03 09:29:06 -0500
commit3d56e331b6537671c66f1b510bed0f1e0331dfc8 (patch)
tree80145576e1b9e701b7a2270c6a09798ed6b783c3 /kernel
parent654986462939cd7ec18f276c6379a334dac106a7 (diff)
tracing: Replace syscall_meta_data struct array with pointer array
Currently the syscall_meta structures for the syscall tracepoints are placed in the __syscall_metadata section, and at link time, the linker makes one large array of all these syscall metadata structures. On boot up, this array is read (much like the initcall sections) and the syscall data is 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 __syscall_metadata 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 __syscall_metadata section is also moved into the .init.data section as it is now only needed at boot up. Suggested-by: David Miller <davem@davemloft.net> Acked-by: David S. Miller <davem@davemloft.net> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
1 files changed, 10 insertions, 9 deletions
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index b706529b4fc7..5c9fe08d2093 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -55,20 +55,21 @@ struct ftrace_event_class event_class_syscall_exit = {
.raw_init = init_syscall_trace,
-extern unsigned long __start_syscalls_metadata[];
-extern unsigned long __stop_syscalls_metadata[];
+extern struct syscall_metadata *__start_syscalls_metadata[];
+extern struct syscall_metadata *__stop_syscalls_metadata[];
static struct syscall_metadata **syscalls_metadata;
-static struct syscall_metadata *find_syscall_meta(unsigned long syscall)
+static __init struct syscall_metadata *
+find_syscall_meta(unsigned long syscall)
- struct syscall_metadata *start;
- struct syscall_metadata *stop;
+ struct syscall_metadata **start;
+ struct syscall_metadata **stop;
char str[KSYM_SYMBOL_LEN];
- start = (struct syscall_metadata *)__start_syscalls_metadata;
- stop = (struct syscall_metadata *)__stop_syscalls_metadata;
+ start = __start_syscalls_metadata;
+ stop = __stop_syscalls_metadata;
kallsyms_lookup(syscall, NULL, NULL, NULL, str);
for ( ; start < stop; start++) {
@@ -78,8 +79,8 @@ static struct syscall_metadata *find_syscall_meta(unsigned long syscall)
* with "SyS" instead of "sys", leading to an unwanted
* mismatch.
- if (start->name && !strcmp(start->name + 3, str + 3))
- return start;
+ if ((*start)->name && !strcmp((*start)->name + 3, str + 3))
+ return *start;
return NULL;