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Merge pull request #224 from riscv-non-isa/rel-table-reorg
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Reorganize relocation table
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@kito-cheng
kito-cheng authored Nov 29, 2021
2 parents 354fa6e + 86cefab commit c3b092b
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189 changes: 130 additions & 59 deletions riscv-elf.adoc
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Expand Up @@ -237,68 +237,139 @@ sequences with their associated relocations in addition to the general purpose
machine word sized relocations that are used for symbol addresses in the
Global Offset Table or DWARF meta data.

The following table provides details of the RISC-V ELF relocations (instruction
specific relocations show the instruction type in the Details column):
<<reloc-table>> provides details of the RISC-V ELF relocations; the meaning of each
column is given below:

[cols=">1,5,2,2,2,3"]
Enum:: The number of the relocation, encoded in the r_info field

ELF Reloc Type:: The name of the relocation, omitted the prefix of `R_RISCV_` here.

Type:: Whether the relocation is a static or runtime relocation:
+
- Static relocations are always resolved by the static linker
- Runtime relocations can be resolved by both static and dynamic linkers

Field:: Describes the set of bits affected by this relocation; see <<Field Symbols>> for the definitions of the individual types

Calculation:: Formula for how to resolve the relocation value; definitions of the
symbols can be found in <<Calculation Symbols>>

Description:: Additional information about the relocation

[[reloc-table]]
[cols=">2,6,3,6,11"]
[width=100%]
|===
| Enum | ELF Reloc Type | Description | Field | Calculation | Details

| 0 | R_RISCV_NONE | None | | |
| 1 | R_RISCV_32 | Runtime relocation | _word32_ | S + A |
| 2 | R_RISCV_64 | Runtime relocation | _word64_ | S + A |
| 3 | R_RISCV_RELATIVE | Runtime relocation | _wordclass_ | B + A |
| 4 | R_RISCV_COPY | Runtime relocation | | | Must be in executable; not allowed in shared library
| 5 | R_RISCV_JUMP_SLOT | Runtime relocation | _wordclass_ | S | Handled by PLT unless `LD_BIND_NOW`
| 6 | R_RISCV_TLS_DTPMOD32 | Runtime TLS relocation | _word32_ | TLSMODULE |
| 7 | R_RISCV_TLS_DTPMOD64 | Runtime TLS relocation | _word64_ | TLSMODULE |
| 8 | R_RISCV_TLS_DTPREL32 | Runtime TLS relocation | _word32_ | S + A - TLS_DTV_OFFSET |
| 9 | R_RISCV_TLS_DTPREL64 | Runtime TLS relocation | _word64_ | S + A - TLS_DTV_OFFSET |
| 10 | R_RISCV_TLS_TPREL32 | Runtime TLS relocation | _word32_ | S + A + TLSOFFSET |
| 11 | R_RISCV_TLS_TPREL64 | Runtime TLS relocation | _word64_ | S + A + TLSOFFSET |
| 16 | R_RISCV_BRANCH | PC-relative branch | _B-Type_ | S + A - P |
| 17 | R_RISCV_JAL | PC-relative jump | _J-Type_ | S + A - P |
| 18 | R_RISCV_CALL | PC-relative call | _U+J-Type_ | S + A - P | Macros `call`, `tail`
| 19 | R_RISCV_CALL_PLT | PC-relative call (PLT) | _U+J-Type_ | S + A - P | Macros `call`, `tail` (PIC)
| 20 | R_RISCV_GOT_HI20 | PC-relative GOT reference | _U-Type_ | G + A - P | `%got_pcrel_hi(symbol)`
| 21 | R_RISCV_TLS_GOT_HI20 | PC-relative TLS IE GOT offset | _U-Type_ | | Macro `la.tls.ie`
| 22 | R_RISCV_TLS_GD_HI20 | PC-relative TLS GD reference | _U-Type_ | | Macro `la.tls.gd`
| 23 | R_RISCV_PCREL_HI20 | PC-relative reference | _U-Type_ | S + A - P | `%pcrel_hi(symbol)`
| 24 | R_RISCV_PCREL_LO12_I | PC-relative reference | _I-type_ | S - P | `%pcrel_lo(address of %pcrel_hi)`, the addend must be 0
| 25 | R_RISCV_PCREL_LO12_S | PC-relative reference | _S-Type_ | S - P | `%pcrel_lo(address of %pcrel_hi)`, the addend must be 0
| 26 | R_RISCV_HI20 | Absolute address | _U-Type_ | S + A | `%hi(symbol)`
| 27 | R_RISCV_LO12_I | Absolute address | _I-Type_ | S + A | `%lo(symbol)`
| 28 | R_RISCV_LO12_S | Absolute address | _S-Type_ | S + A | `%lo(symbol)`
| 29 | R_RISCV_TPREL_HI20 | TLS LE thread offset | _U-Type_ | | `%tprel_hi(symbol)`
| 30 | R_RISCV_TPREL_LO12_I | TLS LE thread offset | _I-Type_ | | `%tprel_lo(symbol)`
| 31 | R_RISCV_TPREL_LO12_S | TLS LE thread offset | _S-Type_ | | `%tprel_lo(symbol)`
| 32 | R_RISCV_TPREL_ADD | TLS LE thread usage | | | `%tprel_add(symbol)`
| 33 | R_RISCV_ADD8 | 8-bit label addition | _word8_ | V + S + A |
| 34 | R_RISCV_ADD16 | 16-bit label addition | _word16_ | V + S + A |
| 35 | R_RISCV_ADD32 | 32-bit label addition | _word32_ | V + S + A |
| 36 | R_RISCV_ADD64 | 64-bit label addition | _word64_ | V + S + A |
| 37 | R_RISCV_SUB8 | 8-bit label subtraction | _word8_ | V - S - A |
| 38 | R_RISCV_SUB16 | 16-bit label subtraction | _word16_ | V - S - A |
| 39 | R_RISCV_SUB32 | 32-bit label subtraction | _word32_ | V - S - A |
| 40 | R_RISCV_SUB64 | 64-bit label subtraction | _word64_ | V - S - A |
| 41 | R_RISCV_GNU_VTINHERIT | GNU {Cpp} vtable hierarchy | | |
| 42 | R_RISCV_GNU_VTENTRY | GNU {Cpp} vtable member usage | | |
| 43 | R_RISCV_ALIGN | Alignment statement | | |
| 44 | R_RISCV_RVC_BRANCH | PC-relative branch offset | _CB-Type_ | S + A - P |
| 45 | R_RISCV_RVC_JUMP | PC-relative jump offset | _CJ-Type_ | S + A - P |
| 46 | R_RISCV_RVC_LUI | Absolute address | _CI-Type_ | S + A |
| 47-50 | *Reserved* | Reserved for future standard use | | |
| 51 | R_RISCV_RELAX | Instruction can be relaxed | | | Paired with a normal relocation at the same address
| 52 | R_RISCV_SUB6 | Local label subtraction | _word6_ | V - S - A |
| 53 | R_RISCV_SET6 | Local label assignment | _word6_ | S + A |
| 54 | R_RISCV_SET8 | Local label assignment | _word8_ | S + A |
| 55 | R_RISCV_SET16 | Local label assignment | _word16_ | S + A |
| 56 | R_RISCV_SET32 | Local label assignment | _word32_ | S + A |
| 57 | R_RISCV_32_PCREL | PC-relative reference | _word32_ | S + A - P |
| 58 | R_RISCV_IRELATIVE | Runtime relocation | _wordclass_ | `ifunc_resolver(B + A)` |
| 59-191 | *Reserved* | Reserved for future standard use | | |
| 192-255 | *Reserved* | Reserved for nonstandard ABI extensions | | |
| Enum | ELF Reloc Type | Type | Field / Calculation | Description

.2+| 0 .2+| NONE .2+| None | .2+|
<|
.2+| 1 .2+| 32 .2+| Runtime | _word32_ .2+| 32-bit relocation
<| S + A
.2+| 2 .2+| 64 .2+| Runtime | _word64_ .2+| 64-bit relocation
<| S + A
.2+| 3 .2+| RELATIVE .2+| Runtime | _wordclass_ .2+| Relocation against a local symbol in a shared object
<| B + A
.2+| 4 .2+| COPY .2+| Runtime | .2+| Must be in executable; not allowed in shared library
<|
.2+| 5 .2+| JUMP_SLOT .2+| Runtime | _wordclass_ .2+| Indicates the symbol associated with a PLT entry
<| S
.2+| 6 .2+| TLS_DTPMOD32 .2+| Runtime | _word32_ .2+|
<| TLSMODULE
.2+| 7 .2+| TLS_DTPMOD64 .2+| Runtime | _word64_ .2+|
<| TLSMODULE
.2+| 8 .2+| TLS_DTPREL32 .2+| Runtime | _word32_ .2+|
<| S + A - TLS_DTV_OFFSET
.2+| 9 .2+| TLS_DTPREL64 .2+| Runtime | _word64_ .2+|
<| S + A - TLS_DTV_OFFSET
.2+| 10 .2+| TLS_TPREL32 .2+| Runtime | _word32_ .2+|
<| S + A + TLSOFFSET
.2+| 11 .2+| TLS_TPREL64 .2+| Runtime | _word64_ .2+|
<| S + A + TLSOFFSET
.2+| 16 .2+| BRANCH .2+| Static | _B-Type_ .2+| 12-bit PC-relative branch offset
<| S + A - P
.2+| 17 .2+| JAL .2+| Static | _J-Type_ .2+| 20-bit PC-relative jump offset
<| S + A - P
.2+| 18 .2+| CALL .2+| Static | _U+J-Type_ .2+| 32-bit PC-relative function call, macros `call`, `tail`
<| S + A - P
.2+| 19 .2+| CALL_PLT .2+| Static | _U+J-Type_ .2+| 32-bit PC-relative function call, macros `call`, `tail` (PIC)
<| S + A - P
.2+| 20 .2+| GOT_HI20 .2+| Static | _U-Type_ .2+| High 20 bits of 32-bit PC-relative GOT access, `%got_pcrel_hi(symbol)`
<| G + A - P
.2+| 21 .2+| TLS_GOT_HI20 .2+| Static | _U-Type_ .2+| High 20 bits of 32-bit PC-relative TLS IE GOT access, macro `la.tls.ie`
<|
.2+| 22 .2+| TLS_GD_HI20 .2+| Static | _U-Type_ .2+| High 20 bits of 32-bit PC-relative TLS GD GOT reference, macro `la.tls.gd`
<|
.2+| 23 .2+| PCREL_HI20 .2+| Static | _U-Type_ .2+| High 20 bits of 32-bit PC-relative reference, `%pcrel_hi(symbol)`
<| S + A - P
.2+| 24 .2+| PCREL_LO12_I .2+| Static | _I-type_ .2+| Low 12 bits of a 32-bit PC-relative, `%pcrel_lo(address of %pcrel_hi)`, the addend must be 0
<| S - P
.2+| 25 .2+| PCREL_LO12_S .2+| Static | _S-Type_ .2+| Low 12 bits of a 32-bit PC-relative, `%pcrel_lo(address of %pcrel_hi)`, the addend must be 0
<| S - P
.2+| 26 .2+| HI20 .2+| Static | _U-Type_ .2+| High 20 bits of 32-bit absolute address, `%hi(symbol)`
<| S + A
.2+| 27 .2+| LO12_I .2+| Static | _I-Type_ .2+| High 12 bits of 32-bit absolute address, `%lo(symbol)`
<| S + A
.2+| 28 .2+| LO12_S .2+| Static | _S-Type_ .2+| High 12 bits of 32-bit absolute address, `%lo(symbol)`
<| S + A
.2+| 29 .2+| TPREL_HI20 .2+| Static | _U-Type_ .2+| High 20 bits of TLS LE thread pointer offset, `%tprel_hi(symbol)`
<|
.2+| 30 .2+| TPREL_LO12_I .2+| Static | _I-Type_ .2+| Low 12 bits of TLS LE thread pointer offset, `%tprel_lo(symbol)`
<|
.2+| 31 .2+| TPREL_LO12_S .2+| Static | _S-Type_ .2+| Low 12 bits of TLS LE thread pointer offset, `%tprel_lo(symbol)`
<|
.2+| 32 .2+| TPREL_ADD .2+| Static | .2+| TLS LE thread pointer usage, `%tprel_add(symbol)`
<|
.2+| 33 .2+| ADD8 .2+| Static | _word8_ .2+| 8-bit label addition
<| V + S + A
.2+| 34 .2+| ADD16 .2+| Static | _word16_ .2+| 16-bit label addition
<| V + S + A
.2+| 35 .2+| ADD32 .2+| Static | _word32_ .2+| 32-bit label addition
<| V + S + A
.2+| 36 .2+| ADD64 .2+| Static | _word64_ .2+| 64-bit label addition
<| V + S + A
.2+| 37 .2+| SUB8 .2+| Static | _word8_ .2+| 8-bit label subtraction
<| V - S - A
.2+| 38 .2+| SUB16 .2+| Static | _word16_ .2+| 16-bit label subtraction
<| V - S - A
.2+| 39 .2+| SUB32 .2+| Static | _word32_ .2+| 32-bit label subtraction
<| V - S - A
.2+| 40 .2+| SUB64 .2+| Static | _word64_ .2+| 64-bit label subtraction
<| V - S - A
.2+| 41 .2+| GNU_VTINHERIT .2+| Static | .2+| GNU {Cpp} vtable hierarchy
<|
.2+| 42 .2+| GNU_VTENTRY .2+| Static | .2+| GNU {Cpp} vtable member usage
<|
.2+| 43 .2+| ALIGN .2+| Static | .2+| Alignment statement
<|
.2+| 44 .2+| RVC_BRANCH .2+| Static | _CB-Type_ .2+| 8-bit PC-relative branch offset
<| S + A - P
.2+| 45 .2+| RVC_JUMP .2+| Static | _CJ-Type_ .2+| 11-bit PC-relative jump offset
<| S + A - P
.2+| 46 .2+| RVC_LUI .2+| Static | _CI-Type_ .2+| High 6 bits of 18-bit absolute address
<| S + A
.2+| 47-50 .2+| *Reserved* .2+| - | .2+| Reserved for future standard use
<|
.2+| 51 .2+| RELAX .2+| Static | .2+| Instruction can be relaxed, paired with a normal relocation at the same address
<|
.2+| 52 .2+| SUB6 .2+| Static | _word6_ .2+| Local label subtraction
<| V - S - A
.2+| 53 .2+| SET6 .2+| Static | _word6_ .2+| Local label assignment
<| S + A
.2+| 54 .2+| SET8 .2+| Static | _word8_ .2+| Local label assignment
<| S + A
.2+| 55 .2+| SET16 .2+| Static | _word16_ .2+| Local label assignment
<| S + A
.2+| 56 .2+| SET32 .2+| Static | _word32_ .2+| Local label assignment
<| S + A
.2+| 57 .2+| 32_PCREL .2+| Static | _word32_ .2+| 32-bit PC relative
<| S + A - P
.2+| 58 .2+| IRELATIVE .2+| Runtime | _wordclass_ .2+| Relocation against a local ifunc symbol in a shared object
<| `ifunc_resolver(B + A)`
.2+| 59-191 .2+| *Reserved* .2+| - | .2+| Reserved for future standard use
<|
.2+| 192-255 .2+| *Reserved* .2+| - | .2+| Reserved for nonstandard ABI extensions
<|
|===

Nonstandard extensions are free to use relocation numbers 192-255 for any
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