samples/ftrace: Fix asm function ELF annotations

Enable objtool coverage for the sample ftrace modules by adding ELF
annotations to the asm trampoline functions.

  samples/ftrace/ftrace-direct.o: warning: objtool: .text+0x0: unreachable instruction
  samples/ftrace/ftrace-direct-modify.o: warning: objtool: .text+0x0: unreachable instruction
  samples/ftrace/ftrace-direct-too.o: warning: objtool: .text+0x0: unreachable instruction

Reported-by: Randy Dunlap <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>

Author: jpoimboe

samples/ftrace/ftrace-direct-modify.c

@@ -20,18 +20,22 @@ static unsigned long my_ip = (unsigned long)schedule;
 
 asm (
 "	.pushsection    .text, \"ax\", @progbits\n"
+"	.type		my_tramp1, @function\n"
 "   my_tramp1:"
 "	pushq %rbp\n"
 "	movq %rsp, %rbp\n"
 "	call my_direct_func1\n"
 "	leave\n"
+"	.size		my_tramp1, .-my_tramp1\n"
 "	ret\n"
+"	.type		my_tramp2, @function\n"
 "   my_tramp2:"
 "	pushq %rbp\n"
 "	movq %rsp, %rbp\n"
 "	call my_direct_func2\n"
 "	leave\n"
 "	ret\n"
+"	.size		my_tramp2, .-my_tramp2\n"
 "	.popsection\n"
 );
 

samples/ftrace/ftrace-direct-too.c

@@ -15,6 +15,7 @@ extern void my_tramp(void *);
 
 asm (
 "	.pushsection    .text, \"ax\", @progbits\n"
+"	.type		my_tramp, @function\n"
 "   my_tramp:"
 "	pushq %rbp\n"
 "	movq %rsp, %rbp\n"
@@ -27,6 +28,7 @@ asm (
 "	popq %rdi\n"
 "	leave\n"
 "	ret\n"
+"	.size		my_tramp, .-my_tramp\n"
 "	.popsection\n"
 );
 

samples/ftrace/ftrace-direct.c

@@ -13,6 +13,7 @@ extern void my_tramp(void *);
 
 asm (
 "	.pushsection    .text, \"ax\", @progbits\n"
+"	.type		my_tramp, @function\n"
 "   my_tramp:"
 "	pushq %rbp\n"
 "	movq %rsp, %rbp\n"
@@ -21,6 +22,7 @@ asm (
 "	popq %rdi\n"
 "	leave\n"
 "	ret\n"
+"	.size		my_tramp, .-my_tramp\n"
 "	.popsection\n"
 );