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| author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2016-03-22 17:30:58 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-04-12 07:33:42 -0700 |
| commit | 085bf9a35c8e102315881a4bd8d2596f8a767739 (patch) | |
| tree | 8e54d4cba8c45dd201aba161ad6e09aef471511a /include | |
| parent | df71f9def05fd07d5c3efafafcec062d37c766ca (diff) | |
| download | lwn-085bf9a35c8e102315881a4bd8d2596f8a767739.tar.gz lwn-085bf9a35c8e102315881a4bd8d2596f8a767739.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()"
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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 f31638c6e873..95452f72349a 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -635,7 +635,7 @@ 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; \ \ @@ -679,7 +679,7 @@ int __trace_printk(unsigned long ip, const char *fmt, ...); */ #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; \ \ @@ -701,7 +701,7 @@ 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; \ \ |