blob: 4320bc22059226cd91b16c7dcdfb6262beb8ceaf (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
|
// SPDX-License-Identifier: GPL-2.0
/*
* A function whose position in the section changes between the two builds,
* without the function itself changing.
*
* target() calls callee() twice, and a call within the same section needs no
* relocation: the displacement is in the instruction. It is that displacement
* which moves, and hashing those bytes makes the checksum move with it. Both
* must therefore share a section, which is why the test passes
* -fno-function-sections.
*
* What has to change is the distance between the two, and PATCHED changes it
* by aligning them rather than by inserting a function between them. Where a
* compiler puts an added function is its own business: gcc emits these in
* source order, so a function written between callee() and target() separates
* them, but clang emits target() immediately before callee() whatever the
* source says, and an added function lands ahead of both. That moves target()
* without moving it relative to callee(), the displacement comes out identical
* in both builds, and the test passes without having asked anything.
*
* Alignment moves the functions apart on both, and moves neither function's
* own instructions -- which is exactly the distinction under test.
*/
#ifdef PATCHED
#define MOVED __attribute__((aligned(64)))
#else
#define MOVED
#endif
static const char __modinfo[]
__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux";
__attribute__((noinline)) MOVED static int callee(int x)
{
return x * 5 + 1;
}
__attribute__((noinline)) MOVED int target(int x)
{
return callee(x) + callee(x + 1);
}
|
