xref: /openbmc/linux/arch/arc/include/asm/jump_label.h (revision 2a598d0b)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _ASM_ARC_JUMP_LABEL_H
3 #define _ASM_ARC_JUMP_LABEL_H
4 
5 #ifndef __ASSEMBLY__
6 
7 #include <linux/stringify.h>
8 #include <linux/types.h>
9 
10 #define JUMP_LABEL_NOP_SIZE 4
11 
12 /*
13  * NOTE about '.balign 4':
14  *
15  * To make atomic update of patched instruction available we need to guarantee
16  * that this instruction doesn't cross L1 cache line boundary.
17  *
18  * As of today we simply align instruction which can be patched by 4 byte using
19  * ".balign 4" directive. In that case patched instruction is aligned with one
20  * 16-bit NOP_S if this is required.
21  * However 'align by 4' directive is much stricter than it actually required.
22  * It's enough that our 32-bit instruction don't cross L1 cache line boundary /
23  * L1 I$ fetch block boundary which can be achieved by using
24  * ".bundle_align_mode" assembler directive. That will save us from adding
25  * useless NOP_S padding in most of the cases.
26  *
27  * TODO: switch to ".bundle_align_mode" directive using whin it will be
28  * supported by ARC toolchain.
29  */
30 
31 static __always_inline bool arch_static_branch(struct static_key *key,
32 					       bool branch)
33 {
34 	asm_volatile_goto(".balign "__stringify(JUMP_LABEL_NOP_SIZE)"	\n"
35 		 "1:							\n"
36 		 "nop							\n"
37 		 ".pushsection __jump_table, \"aw\"			\n"
38 		 ".word 1b, %l[l_yes], %c0				\n"
39 		 ".popsection						\n"
40 		 : : "i" (&((char *)key)[branch]) : : l_yes);
41 
42 	return false;
43 l_yes:
44 	return true;
45 }
46 
47 static __always_inline bool arch_static_branch_jump(struct static_key *key,
48 						    bool branch)
49 {
50 	asm_volatile_goto(".balign "__stringify(JUMP_LABEL_NOP_SIZE)"	\n"
51 		 "1:							\n"
52 		 "b %l[l_yes]						\n"
53 		 ".pushsection __jump_table, \"aw\"			\n"
54 		 ".word 1b, %l[l_yes], %c0				\n"
55 		 ".popsection						\n"
56 		 : : "i" (&((char *)key)[branch]) : : l_yes);
57 
58 	return false;
59 l_yes:
60 	return true;
61 }
62 
63 typedef u32 jump_label_t;
64 
65 struct jump_entry {
66 	jump_label_t code;
67 	jump_label_t target;
68 	jump_label_t key;
69 };
70 
71 #endif  /* __ASSEMBLY__ */
72 #endif
73