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| author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2016-03-22 17:30:58 -0400 |
|---|---|---|
| committer | Willy Tarreau <w@1wt.eu> | 2016-06-07 10:42:47 +0200 |
| commit | 2ec6dac110fe364dfc6ba140ba4ec3f4f47bbb3d (patch) | |
| tree | 9d827ed492576e5678a9412a69d97030bf293f04 /include | |
| parent | 3f3f1fce3c1af5720308ec83a3d2ffb328a028aa (diff) | |
| download | lwn-2ec6dac110fe364dfc6ba140ba4ec3f4f47bbb3d.tar.gz lwn-2ec6dac110fe364dfc6ba140ba4ec3f4f47bbb3d.zip | |
tracing: Fix trace_printk() to print when not using bprintk()
commit 3debb0a9ddb16526de8b456491b7db60114f7b5e upstream.
The trace_printk() code will allocate extra buffers if the compile detects
that a trace_printk() is used. To do this, the format of the trace_printk()
is saved to the __trace_printk_fmt section, and if that section is bigger
than zero, the buffers are allocated (along with a message that this has
happened).
If trace_printk() uses a format that is not a constant, and thus something
not guaranteed to be around when the print happens, the compiler optimizes
the fmt out, as it is not used, and the __trace_printk_fmt section is not
filled. This means the kernel will not allocate the special buffers needed
for the trace_printk() and the trace_printk() will not write anything to the
tracing buffer.
Adding a "__used" to the variable in the __trace_printk_fmt section will
keep it around, even though it is set to NULL. This will keep the string
from being printed in the debugfs/tracing/printk_formats section as it is
not needed.
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Fixes: 07d777fe8c398 "tracing: Add percpu buffers for trace_printk()"
Cc: stable@vger.kernel.org # v3.5+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/kernel.h | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 341551c7b4c8..5f4554b8348a 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -557,7 +557,7 @@ do { \ #define do_trace_printk(fmt, args...) \ do { \ - static const char *trace_printk_fmt \ + static const char *trace_printk_fmt __used \ __attribute__((section("__trace_printk_fmt"))) = \ __builtin_constant_p(fmt) ? fmt : NULL; \ \ @@ -604,7 +604,7 @@ extern int __trace_puts(unsigned long ip, const char *str, int size); */ #define trace_puts(str) ({ \ - static const char *trace_printk_fmt \ + static const char *trace_printk_fmt __used \ __attribute__((section("__trace_printk_fmt"))) = \ __builtin_constant_p(str) ? str : NULL; \ \ @@ -624,7 +624,7 @@ extern void trace_dump_stack(int skip); #define ftrace_vprintk(fmt, vargs) \ do { \ if (__builtin_constant_p(fmt)) { \ - static const char *trace_printk_fmt \ + static const char *trace_printk_fmt __used \ __attribute__((section("__trace_printk_fmt"))) = \ __builtin_constant_p(fmt) ? fmt : NULL; \ \ |