7.8. ELF 可重定位

重定位（Relocation）是计算机程序在内存中动态调整代码和数据地址的过程，
将程序中的逻辑地址（编译时生成的地址）转换为虚拟地址（内存中的实际地址）的过程，
确保程序在不同内存位置运行时仍能正确执行。

本章节主要会讲解有关龙架构相关的可重定位类型及其具体的操作。

7.8.1. 可重定位类型（Relocation Type）

下面是所有关于LoongArch的可重定位的类型[1]。

/* LoongArch specific dynamic relocations */
#define R_LARCH_NONE		0
#define R_LARCH_32		1
#define R_LARCH_64		2
#define R_LARCH_RELATIVE	3
#define R_LARCH_COPY		4
#define R_LARCH_JUMP_SLOT	5
#define R_LARCH_TLS_DTPMOD32	6
#define R_LARCH_TLS_DTPMOD64	7
#define R_LARCH_TLS_DTPREL32	8
#define R_LARCH_TLS_DTPREL64	9
#define R_LARCH_TLS_TPREL32	10
#define R_LARCH_TLS_TPREL64	11
#define R_LARCH_IRELATIVE	12
#define R_LARCH_TLS_DESC32	13
#define R_LARCH_TLS_DESC64	14

/* Reserved for future relocs that the dynamic linker must understand.  */

/* used by the static linker for relocating .text.  */
#define R_LARCH_MARK_LA  20
#define R_LARCH_MARK_PCREL  21
#define R_LARCH_SOP_PUSH_PCREL  22
#define R_LARCH_SOP_PUSH_ABSOLUTE  23
#define R_LARCH_SOP_PUSH_DUP  24
#define R_LARCH_SOP_PUSH_GPREL  25
#define R_LARCH_SOP_PUSH_TLS_TPREL  26
#define R_LARCH_SOP_PUSH_TLS_GOT  27
#define R_LARCH_SOP_PUSH_TLS_GD  28
#define R_LARCH_SOP_PUSH_PLT_PCREL  29
#define R_LARCH_SOP_ASSERT  30
#define R_LARCH_SOP_NOT  31
#define R_LARCH_SOP_SUB  32
#define R_LARCH_SOP_SL  33
#define R_LARCH_SOP_SR  34
#define R_LARCH_SOP_ADD  35
#define R_LARCH_SOP_AND  36
#define R_LARCH_SOP_IF_ELSE  37
#define R_LARCH_SOP_POP_32_S_10_5  38
#define R_LARCH_SOP_POP_32_U_10_12  39
#define R_LARCH_SOP_POP_32_S_10_12  40
#define R_LARCH_SOP_POP_32_S_10_16  41
#define R_LARCH_SOP_POP_32_S_10_16_S2  42
#define R_LARCH_SOP_POP_32_S_5_20  43
#define R_LARCH_SOP_POP_32_S_0_5_10_16_S2  44
#define R_LARCH_SOP_POP_32_S_0_10_10_16_S2  45
#define R_LARCH_SOP_POP_32_U  46

/* used by the static linker for relocating non .text.  */
#define R_LARCH_ADD8  47
#define R_LARCH_ADD16  48
#define R_LARCH_ADD24  49
#define R_LARCH_ADD32  50
#define R_LARCH_ADD64  51
#define R_LARCH_SUB8  52
#define R_LARCH_SUB16  53
#define R_LARCH_SUB24  54
#define R_LARCH_SUB32  55
#define R_LARCH_SUB64  56
#define R_LARCH_GNU_VTINHERIT  57
#define R_LARCH_GNU_VTENTRY  58

/* reserved 59-63 */

#define R_LARCH_B16 64
#define R_LARCH_B21 65
#define R_LARCH_B26 66
#define R_LARCH_ABS_HI20 67
#define R_LARCH_ABS_LO12 68
#define R_LARCH_ABS64_LO20 69
#define R_LARCH_ABS64_HI12 70
#define R_LARCH_PCALA_HI20 71
#define R_LARCH_PCALA_LO12 72
#define R_LARCH_PCALA64_LO20 73
#define R_LARCH_PCALA64_HI12 74
#define R_LARCH_GOT_PC_HI20 75
#define R_LARCH_GOT_PC_LO12 76
#define R_LARCH_GOT64_PC_LO20 77
#define R_LARCH_GOT64_PC_HI12 78
#define R_LARCH_GOT_HI20 79
#define R_LARCH_GOT_LO12 80
#define R_LARCH_GOT64_LO20 81
#define R_LARCH_GOT64_HI12 82
#define R_LARCH_TLS_LE_HI20 83
#define R_LARCH_TLS_LE_LO12 84
#define R_LARCH_TLS_LE64_LO20 85
#define R_LARCH_TLS_LE64_HI12 86
#define R_LARCH_TLS_IE_PC_HI20 87
#define R_LARCH_TLS_IE_PC_LO12 88
#define R_LARCH_TLS_IE64_PC_LO20 89
#define R_LARCH_TLS_IE64_PC_HI12 90
#define R_LARCH_TLS_IE_HI20 91
#define R_LARCH_TLS_IE_LO12 92
#define R_LARCH_TLS_IE64_LO20 93
#define R_LARCH_TLS_IE64_HI12 94
#define R_LARCH_TLS_LD_PC_HI20 95
#define R_LARCH_TLS_LD_HI20 96
#define R_LARCH_TLS_GD_PC_HI20 97
#define R_LARCH_TLS_GD_HI20 98
#define R_LARCH_32_PCREL 99
#define R_LARCH_RELAX 100
#define R_LARCH_DELETE 101
#define R_LARCH_ALIGN 102
#define R_LARCH_PCREL20_S2 103
#define R_LARCH_CFA 104
#define R_LARCH_ADD6 105
#define R_LARCH_SUB6 106
#define R_LARCH_ADD_ULEB128 107
#define R_LARCH_SUB_ULEB128 108
#define R_LARCH_64_PCREL 109
#define R_LARCH_CALL36 110
#define R_LARCH_TLS_DESC_PC_HI20 111
#define R_LARCH_TLS_DESC_PC_LO12 112
#define R_LARCH_TLS_DESC64_PC_LO20 113
#define R_LARCH_TLS_DESC64_PC_HI12 114
#define R_LARCH_TLS_DESC_HI20 115
#define R_LARCH_TLS_DESC_LO12 116
#define R_LARCH_TLS_DESC64_LO20 117
#define R_LARCH_TLS_DESC64_HI12 118
#define R_LARCH_TLS_DESC_LD 119
#define R_LARCH_TLS_DESC_CALL 120
#define R_LARCH_TLS_LE_HI20_R 121
#define R_LARCH_TLS_LE_ADD_R 122
#define R_LARCH_TLS_LE_LO12_R 123
#define R_LARCH_TLS_LD_PCREL20_S2 124
#define R_LARCH_TLS_GD_PCREL20_S2 125
#define R_LARCH_TLS_DESC_PCREL20_S2 126

重定位的类型主要分为两大类：

  • 静态重定位（Static Relocation）

    主要是由链接器使用（ld），将各个的.o文件合并成一个可执行文件时使用。

  • 动态重定位（Dynamic Relocation）

    主要是程序在加载或者执行过程中(loader)，将各个需要重定位的符号解析，按照
    类型定义，重新获得地址。此过程主要是运行过程中处理。