samples/ftrace: Mark my_tramp[12]? global

my_tramp[12]? are declared as global functions in C, but they are not
marked global in the inline assembly definition. This mismatch confuses
Clang's Control-Flow Integrity checking. Fix the definitions by adding
.globl.

Link: https://lkml.kernel.org/r/20201113183414.1446671-1-samitolvanen@google.com

Fixes: 9d907f1ae8 ("ftrace/samples: Add a sample module that implements modify_ftrace_direct()")
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

samples/ftrace/ftrace-direct-modify.c

@@ -21,6 +21,7 @@ static unsigned long my_ip = (unsigned long)schedule;
 asm (
 "	.pushsection    .text, \"ax\", @progbits\n"
 "	.type		my_tramp1, @function\n"
+"	.globl		my_tramp1\n"
 "   my_tramp1:"
 "	pushq %rbp\n"
 "	movq %rsp, %rbp\n"
@@ -29,6 +30,7 @@ asm (
 "	.size		my_tramp1, .-my_tramp1\n"
 "	ret\n"
 "	.type		my_tramp2, @function\n"
+"	.globl		my_tramp2\n"
 "   my_tramp2:"
 "	pushq %rbp\n"
 "	movq %rsp, %rbp\n"

samples/ftrace/ftrace-direct-too.c

@@ -16,6 +16,7 @@ extern void my_tramp(void *);
 asm (
 "	.pushsection    .text, \"ax\", @progbits\n"
 "	.type		my_tramp, @function\n"
+"	.globl		my_tramp\n"
 "   my_tramp:"
 "	pushq %rbp\n"
 "	movq %rsp, %rbp\n"

samples/ftrace/ftrace-direct.c

@@ -14,6 +14,7 @@ extern void my_tramp(void *);
 asm (
 "	.pushsection    .text, \"ax\", @progbits\n"
 "	.type		my_tramp, @function\n"
+"	.globl		my_tramp\n"
 "   my_tramp:"
 "	pushq %rbp\n"
 "	movq %rsp, %rbp\n"