From c1741786f32c0008200add1fcc86ca087b681504 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Thu, 30 Jul 2020 15:45:54 -0700 Subject: tracepoint: Mark __tracepoint_string's __used commit f3751ad0116fb6881f2c3c957d66a9327f69cefb upstream. __tracepoint_string's have their string data stored in .rodata, and an address to that data stored in the "__tracepoint_str" section. Functions that refer to those strings refer to the symbol of the address. Compiler optimization can replace those address references with references directly to the string data. If the address doesn't appear to have other uses, then it appears dead to the compiler and is removed. This can break the /tracing/printk_formats sysfs node which iterates the addresses stored in the "__tracepoint_str" section. Like other strings stored in custom sections in this header, mark these __used to inform the compiler that there are other non-obvious users of the address, so they should still be emitted. Link: https://lkml.kernel.org/r/20200730224555.2142154-2-ndesaulniers@google.com Cc: Ingo Molnar Cc: Miguel Ojeda Cc: stable@vger.kernel.org Fixes: 102c9323c35a8 ("tracing: Add __tracepoint_string() to export string pointers") Reported-by: Tim Murray Reported-by: Simon MacMullen Suggested-by: Greg Hackmann Signed-off-by: Nick Desaulniers Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Greg Kroah-Hartman --- include/linux/tracepoint.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index 27e32b2b602f..d7875d312f1f 100644 --- a/include/linux/tracepoint.h +++ b/include/linux/tracepoint.h @@ -328,7 +328,7 @@ extern void syscall_unregfunc(void); static const char *___tp_str __tracepoint_string = str; \ ___tp_str; \ }) -#define __tracepoint_string __attribute__((section("__tracepoint_str"))) +#define __tracepoint_string __attribute__((section("__tracepoint_str"), used)) #else /* * tracepoint_string() is used to save the string address for userspace -- cgit v1.2.3