Relocation information is used by linkers to bind symbols and addresses that could not be determined when the initial object was generated.
Relocation entries describe how to alter the instruction and data relocation fields Relocations applied to executable or shared object files are similar and accomplish the same result.
All relocations are listed and described in the following table, including the operation performed to compute the value of the relocation.
| Code | Name | Description | Operation |
|---|---|---|---|
| 1 | R_MICROBLAZE_NONE | This relocation does nothing. | none |
| 2 | R_MICROBLAZE_32 | A standard 32 bit relocation. | S+A |
| 3 | R_MICROBLAZE_32_PCREL | A standard PCREL 32 bit relocation. | S+A-P |
| 4 | R_MICROBLAZE_64_PCREL | A 64 bit PCREL relocation. Table-entry only used for 64-bit implementation. | (S+A-P)&0xFFFF (#imm) |
| 5 | R_MICROBLAZE_32_PCREL_LO | The low half of a PCREL 32 bit relocation. | (S+A-P)&0xFFFF |
| 6 | R_MICROBLAZE_64 | A 64 bit relocation. Table entry only used for 64-bit implementation. | (S+A)&0xFFFF (#imm) |
| 7 | R_MICROBLAZE_32_LO | The low half of a 32 bit relocation. | (S+A)&0xFFFF |
| 8 | R_MICROBLAZE_SRO32 | Read-only small data section relocation. | (S+A -_SDA_BASE_) |
| 9 | R_MICROBLAZE_SRW32 | Read-write small data area relocation. | (S+A-_SDA_BASE_) |
| 10 | R_MICROBLAZE_64_NONE | This relocation does nothing. Used for relaxation. | none |
| 11 | R_MICROBLAZE_32_SYM_OP_SYM | Symbol Op Symbol relocation. | none |
| 12 | R_MICROBLAZE_GNU_VTINHERIT | GNU extension to record C++ vtable hierarchy. | |
| 13 | R_MICROBLAZE_GNU_VTENTRY | GNU extension to record C++ vtable member usage. | |
| 14 | R_MICROBLAZE_GOTPC_64 | A 64 bit GOTPC relocation. Table-entry only used for 64-bit implementation. | G+A–P (#imm) |
| 15 | R_MICROBLAZE_GOT_64 | A 64 bit GOT relocation. Table-entry only used for 64-bit implementation. | G+A (#imm) |
| 16 | R_MICROBLAZE_PLT_64 | A 64 bit PLT relocation. Table-entry only used for 64-bit implementation. | L+A (#imm) |
| 17 | R_MICROBLAZE_REL | Table-entry not used. | ((B + A)>>16) & 0xFFFF |
| 18 | R_MICROBLAZE_JUMP_SLOT | Table-entry not used. | (S >> 16) & 0xFFFF |
| 19 | R_MICROBLAZE_GLOB_DAT | Table-entry not used. | (S >> 16) & 0xFFFF |
| 20 | R_MICROBLAZE_GOTOFF_64 | A 64 bit GOT relative relocation. | (S+A-GOT)&0xFFFF |
| 21 | R_MICROBLAZE_GOTOFF_32 | A 32 bit GOT relative relocation. | (S+A-GOT)&0xFFFF |
| 22 | R_MICROBLAZE_COPY | COPY relocation. | none |
| 23 | R_MICROBLAZE_TLS | TLS relocations for TLS. | none |
| 24 | R_MICROBLAZE_TLSGD | TLSGD relocations for TLS. | @got@tlsgd |
| 25 | R_MICROBLAZE_TLSLD | TLSLD relocations for TLS. | @got@tlsld |
| 26 | R_MICROBLAZE_TLSDTPMOD32 | Computes the load module. | @got@dtpmod |
| 27 | R_MICROBLAZE_TLSDTPREL32 | Computes a dtv-relative displacement. | @got@dtprel |
| 28 | R_MICROBLAZE_TLSDTPREL64 | Computes a dtv-relative displacement. | @got@dtprel |
| 29 | R_MICROBLAZE_TLSGOTTPREL32 | Computes a tp-relative displacement. | @got@prel |
| 30 | R_MICROBLAZE_TLSTPREL32 | Computes a tp-relative displacement. | @got@prel |
| 31 | R_MICROBLAZE_32_NONE | Standard 32-bit relocation. | none |
The symbol nomenclature and relocation calculations with thread-local symbols used in the relocation entries table are explained in the following table.
| Symbol | Meaning |
|---|---|
| A | The addend used to compute the value of the relocatable field. |
| B | The base address at which a shared object has been loaded into memory during execution. Generally, a shared object file is built with a 0 base virtual address, but the execution address will be different. |
| G | The offset into the global offset table at which the address of the relocation entry’s symbol will reside during execution. |
| GOT | The address of the global offset table. |
| L | The place (section offset or address) of the procedure linkage table entry for a symbol. A procedure linkage table entry redirects a function call to the proper destination. The link editor builds the initial procedure linkage table, and the dynamic linker modifies the entries during execution. |
| P | The place (section offset or address) of the storage unit being relocated (computed using r_offset). |
| S | The value of the symbol whose index resides in the relocation entry. |
| @dtpmod | Computes the load module index of the load module that contain the definition of a symbol. The addend, if present, is ignored |
| @dtprel | Computes a dtv-relative displacement, the difference between the value of S + A and the base address of the thread-local storage block that contains the definition of the symbol, minus 0x8000. |
| @got@tlsgd | Allocates entries in the GOT to hold a tls_index structure, with values @dtpmod and @dtprel, and computes the offset to the first entry relative to the TOC base. |
| @got@tlsld | Allocates entries in the GOT to hold a tls_index structure, with values @dtpmod and zero, and computes the offset to the first entry relative to the TOC base. |
| @got@dtpmod | Computes the load module index of the load module that contains the definition of its TLS symbol. |
| @got@dtprel | Computes a dtv-relative displacement, the difference between the value of symbol + add and the base address of the thread-local storage block that contains the definition of the symbol, minus 0x8000. Used for initializing GOT. |
| @got@prel | Computes a tp-relative displacement, the difference between the value of symbol + add and the value of the thread pointer (r13). |
| #imm | Inserts imm instruction if the immediate value is greater than 16 bits in the instruction. |