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311927f1 | 1 | /* PLT fixups. Sparc 32-bit version. |
b168057a | 2 | Copyright (C) 1996-2015 Free Software Foundation, Inc. |
311927f1 DM |
3 | This file is part of the GNU C Library. |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
59ba27a6 PE |
16 | License along with the GNU C Library; if not, see |
17 | <http://www.gnu.org/licenses/>. */ | |
311927f1 | 18 | |
42675c6f DM |
19 | #ifndef _DL_PLT_H |
20 | #define _DL_PLT_H | |
21 | ||
311927f1 DM |
22 | /* Some SPARC opcodes we need to use for self-modifying code. */ |
23 | #define OPCODE_NOP 0x01000000 /* nop */ | |
24 | #define OPCODE_CALL 0x40000000 /* call ?; add PC-rel word address */ | |
25 | #define OPCODE_SETHI_G1 0x03000000 /* sethi ?, %g1; add value>>10 */ | |
26 | #define OPCODE_JMP_G1 0x81c06000 /* jmp %g1+?; add lo 10 bits of value */ | |
27 | #define OPCODE_SAVE_SP 0x9de3bfa8 /* save %sp, -(16+6)*4, %sp */ | |
28 | #define OPCODE_BA 0x30800000 /* b,a ?; add PC-rel word address */ | |
7ec1221f | 29 | #define OPCODE_BA_PT 0x30480000 /* ba,a,pt %icc, ?; add PC-rel word address */ |
311927f1 DM |
30 | |
31 | static inline __attribute__ ((always_inline)) Elf32_Addr | |
32 | sparc_fixup_plt (const Elf32_Rela *reloc, Elf32_Addr *reloc_addr, | |
33 | Elf32_Addr value, int t, int do_flush) | |
34 | { | |
7ec1221f | 35 | Elf32_Sword disp; |
311927f1 | 36 | |
7ec1221f DM |
37 | /* 't' is '0' if we are resolving this PLT entry for RTLD bootstrap, |
38 | in which case we'll be resolving all PLT entries and thus can | |
39 | optimize by overwriting instructions starting at the first PLT entry | |
40 | instruction and we need not be mindful of thread safety. | |
41 | ||
42 | Otherwise, 't' is '1'. */ | |
43 | reloc_addr += t; | |
44 | disp = value - (Elf32_Addr) reloc_addr; | |
45 | ||
46 | if (disp >= -0x800000 && disp < 0x800000) | |
311927f1 | 47 | { |
7ec1221f DM |
48 | unsigned int insn = OPCODE_BA | ((disp >> 2) & 0x3fffff); |
49 | ||
50 | #ifdef __sparc_v9__ | |
51 | /* On V9 we can do even better by using a branch with | |
52 | prediction if we fit into the even smaller 19-bit | |
53 | displacement field. */ | |
54 | if (disp >= -0x100000 && disp < 0x100000) | |
55 | insn = OPCODE_BA_PT | ((disp >> 2) & 0x07ffff); | |
56 | #endif | |
57 | ||
58 | /* Even if we are writing just a single branch, we must not | |
59 | ignore the 't' offset. Consider a case where we have some | |
60 | PLT slots which can be optimized into a single branch and | |
61 | some which cannot. Then we can end up with a PLT which looks | |
62 | like: | |
63 | ||
64 | PLT4.0: sethi %(PLT_4_INDEX), %g1 | |
65 | sethi %(fully_resolved_sym_4), %g1 | |
66 | jmp %g1 + %lo(fully_resolved_sym_4) | |
67 | PLT5.0: ba,a fully_resolved_sym_5 | |
68 | ba,a PLT0.0 | |
69 | ... | |
70 | ||
71 | The delay slot of that jmp must always be either a sethi to | |
72 | %g1 or a nop. But if we try to place this displacement | |
73 | branch there, PLT4.0 will jump to fully_resolved_sym_4 for 1 | |
74 | instruction and then go immediately to | |
75 | fully_resolved_sym_5. */ | |
311927f1 | 76 | |
7ec1221f | 77 | reloc_addr[0] = insn; |
311927f1 DM |
78 | if (do_flush) |
79 | __asm __volatile ("flush %0" : : "r"(reloc_addr)); | |
80 | } | |
81 | else | |
82 | { | |
83 | /* For thread safety, write the instructions from the bottom and | |
84 | flush before we overwrite the critical "b,a". This of course | |
85 | need not be done during bootstrapping, since there are no threads. | |
86 | But we also can't tell if we _can_ use flush, so don't. */ | |
87 | ||
311927f1 DM |
88 | reloc_addr[1] = OPCODE_JMP_G1 | (value & 0x3ff); |
89 | if (do_flush) | |
90 | __asm __volatile ("flush %0+4" : : "r"(reloc_addr)); | |
91 | ||
92 | reloc_addr[0] = OPCODE_SETHI_G1 | (value >> 10); | |
93 | if (do_flush) | |
94 | __asm __volatile ("flush %0" : : "r"(reloc_addr)); | |
95 | } | |
96 | ||
97 | return value; | |
98 | } | |
42675c6f DM |
99 | |
100 | #endif /* dl-plt.h */ |