r_offset

This member gives the location at which to apply the relocation action. Different object files have slightly different interpretations for this member.

For a relocatable file, the value indicates a section offset. The relocation section itself describes how to modify another section in the file. Relocation offsets designate a storage unit within the second section.

For an executable or shared object, the value indicates the virtual address of the storage unit affected by the relocation. This information makes the relocation entries more useful for the runtime linker.

Although the interpretation of the member changes for different object files to allow efficient access by the relevant programs, the meanings of the relocation types stay the same.

r_info

This member gives both the symbol table index, with respect to which the relocation must be made, and the type of relocation to apply. For example, a call instruction's relocation entry will hold the symbol table index of the function being called. If the index is STN_UNDEF, the undefined symbol index, the relocation uses 0 as the symbol value.

Relocation types are processor-specific. A relocation entry's relocation type or symbol table index is the result of applying ELF32_R_TYPE or ELF32_R_SYM, respectively, to the entry's r_info member:

#define ELF32_R_SYM(info) ((info)>>8) #define ELF32_R_TYPE(info) ((unsigned char)(info)) #define ELF32_R_INFO(sym, type) (((sym)<<8)+(unsigned char)(type)) #define ELF64_R_SYM(info) ((info)>>32) #define ELF64_R_TYPE(info) ((Elf64_Word)(info)) #define ELF64_R_INFO(sym, type) (((Elf64_Xword)(sym)<<32)+ \ (Elf64_Xword)(type))

For Elf64_Rel and Elf64_Rela structures, the r_info field is further broken down into an 8-bit type identifier and a 24-bit type dependent data field:

#define ELF64_R_TYPE_DATA(info) (((Elf64_Xword)(info)<<32)>>40) #define ELF64_R_TYPE_ID(info) (((Elf64_Xword)(info)<<56)>>56) #define ELF64_R_TYPE_INFO(data, type) (((Elf64_Xword)(data)<<8)+ \ (Elf64_Xword)(type))

r_addend

This member specifies a constant addend used to compute the value to be stored into the relocatable field.

Rela entries contain an explicit addend. Entries of type Rel store an implicit addend in the location to be modified. 32-bit and 64-bit SPARC use only Elf32_Rela and Elf64_Rela relocation entries respectively. Thus, the r_addend member serves as the relocation addend. IA uses only Elf32_Rel relocation entries. The field to be relocated holds the addend. In all cases, the addend and the computed result use the same byte order.

A relocation section can reference two other sections: a symbol table, identified by the sh_info section header entry, and a section to modify, identified by the sh_link section header entry. "Sections" specifies these relationships. An sh_link entry is required when a relocation section exists in a relocatable object, but is optional for executables and shared objects. The relocation offset is sufficient to perform the relocation.

Relocation Types (Processor-Specific)

Relocation entries describe how to alter instruction and data fields in the following figures. Bit numbers appear in the lower box corners.

On the SPARC platform, relocation entries apply to bytes (byte8), half-words (half16), or words (the others).

On 64-bit SPARC, relocations also apply to extended-words (xword64):

On IA, relocation entries apply to words (word32):

word32 specifies a 32-bit field occupying 4 bytes with an arbitrary byte alignment. These values use the same byte order as other word values in the IA architecture:

In all cases, the r_offset value designates the offset or virtual address of the first byte of the affected storage unit. The relocation type specifies which bits to change and how to calculate their values.

Calculations for the following relocation types assume the actions are transforming a relocatable file into either an executable or a shared object file. Conceptually, the link-editor merges one or more relocatable files to form the output. The link-editor first decides how to combine and locate the input files. Then it updates the symbol values. Finally the link-editor performs the relocation. Relocations applied to executable or shared object files are similar and accomplish the same result. Descriptions in the tables in this section use the following notation:

A	The addend used to compute the value of the relocatable field.
B	The base address at which a shared object is loaded into memory during execution. Generally, a shared object file is built with a 0 base virtual address, but the execution address is different. See "Program Header".
G	The offset into the global offset table at which the address of the relocation entry's symbol resides during execution. See "Global Offset Table (Processor-Specific)".
GOT	The address of the global offset table. See "Global Offset Table (Processor-Specific)".
L	The section offset or address of the procedure linkage table entry for a symbol. See "Procedure Linkage Table (Processor-Specific)".
P	The 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.

SPARC: Relocation Types

Field names in the following table tell whether the relocation type checks for overflow. A calculated relocation value can be larger than the intended field, and a relocation type can verify (V) the value fits or truncate (T) the result. As an example, V-simm13 means that the computed value can not have significant, nonzero bits outside the simm13 field.

Table 7-27 SPARC: ELF Relocation Types

Name	Value	Field	Calculation
R_SPARC_NONE	0	None	None
R_SPARC_8	1	V-byte8	S + A
R_SPARC_16	2	V-half16	S + A
R_SPARC_32	3	V-word32	S + A
R_SPARC_DISP8	4	V-byte8	S + A - P
R_SPARC_DISP16	5	V-half16	S + A - P
R_SPARC_DISP32	6	V-disp32	S + A - P
R_SPARC_WDISP30	7	V-disp30	(S + A - P) >> 2
R_SPARC_WDISP22	8	V-disp22	(S + A - P) >> 2
R_SPARC_HI22	9	T-imm22	(S + A) >> 10
R_SPARC_22	10	V-imm22	S + A
R_SPARC_13	11	V-simm13	S + A
R_SPARC_LO10	12	T-simm13	(S + A) & 0x3ff
R_SPARC_GOT10	13	T-simm13	G & 0x3ff
R_SPARC_GOT13	14	V-simm13	G
R_SPARC_GOT22	15	T-simm22	G >> 10
R_SPARC_PC10	16	T-simm13	(S + A - P) & 0x3ff
R_SPARC_PC22	17	V-disp22	(S + A - P) >> 10
R_SPARC_WPLT30	18	V-disp30	(L + A - P) >> 2
R_SPARC_COPY	19	None	None
R_SPARC_GLOB_DAT	20	V-word32	S + A
R_SPARC_JMP_SLOT	21	None	See R_SPARC_JMP_SLOT,
R_SPARC_RELATIVE	22	V-word32	B + A
R_SPARC_UA32	23	V-word32	S + A
R_SPARC_PLT32	24	V-word32	L + A
R_SPARC_HIPLT22	25	T-imm22	(L + A) >> 10
R_SPARC_LOPLT10	26	T-simm13	(L + A) & 0x3ff
R_SPARC_PCPLT32	27	V-word32	L + A - P
R_SPARC_PCPLT22	28	V-disp22	(L + A - P) >> 10
R_SPARC_PCPLT10	29	V-simm13	(L + A - P) & 0x3ff
R_SPARC_10	30	V-simm10	S + A
R_SPARC_11	31	V-simm11	S + A
R_SPARC_OLO10	33	V-simm13	((S + A) & 0x3ff) + O
R_SPARC_HH22	34	V-imm22	(S + A) >> 42
R_SPARC_HM10	35	T-simm13	((S + A) >> 32) & 0x3ff
R_SPARC_LM22	36	T-imm22	(S + A) >> 10
R_SPARC_PC_HH22	37	V-imm22	(S + A - P) >> 42
R_SPARC_PC_HM10	38	T-simm13	((S + A - P) >> 32) & 0x3ff
R_SPARC_PC_LM22	39	T-imm22	(S + A - P) >> 10
R_SPARC_WDISP16	40	V-d2/disp14	(S + A - P) >> 2
R_SPARC_WDISP19	41	V-disp19	(S + A - P) >> 2
R_SPARC_7	43	V-imm7	S + A
R_SPARC_5	44	V-imm5	S + A
R_SPARC_6	45	V-imm6	S + A
R_SPARC_HIX22	48	V-imm22	((S + A) ^ 0xffffffffffffffff) >> 10
R_SPARC_LOX10	49	T-simm13	((S + A) & 0x3ff) | 0x1c00
R_SPARC_H44	50	V-imm22	(S + A) >> 22
R_SPARC_M44	51	T-imm10	((S + A) >> 12) & 0x3ff
R_SPARC_L44	52	T-imm13	(S + A) & 0xfff
R_SPARC_REGISTER	53	V-word32	S + A
R_SPARC_UA16	55	V-half16	S + A

Some relocation types have semantics beyond simple calculation: