OS X ABI Mach-O File Format Reference

Data Types

scattered_relocation_info

Describes an item in the file—using a nonzero constant in its relocatable expression or two addresses in its relocatable expression—that needs to be updated if the addresses that it uses are changed. This information is needed to reconstruct the addresses that make up the relocatable expression’s value in order to change the addresses independently of each other. Declared in /usr/include/mach-o/reloc.h.

struct scattered_relocation_info

{

#ifdef __BIG_ENDIAN__ uint32_t r_scattered:1, r_pcrel:1,

r_length:2, r_type:4, r_address:24; int32_t r_value;

#endif /* __BIG_ENDIAN__ */ #ifdef __LITTLE_ENDIAN__ uint32_t r_address:24, r_type:4,

r_length:2, r_pcrel:1, r_scattered:1; int32_t r_value;

#endif /* __LITTLE_ENDIAN__ */ };

Fields

r_scattered

If this bit is 0, this structure is actually a relocation_info (page 58) structure.

r_address

In MH_OBJECT files, this is an offset from the start of the section to the item containing the address requiring relocation. If the high bit of this field is clear (which you can check using the R_SCATTERED bit mask), this structure is actually a relocation_info (page 58) structure.

In images used by the dynamic linker, this is an offset from the virtual memory address of the data of the first segment_command (page 19)thatappearsinthefile(notnecessarilytheonewiththelowestaddress). For images with the MH_SPLIT_SEGS flag set, this is an offset from the virtual memory address of data of the first read/write segment_command (page 19).

Since this field is only 24 bits long, the offset in this field can never be larger than 0x00FFFFFF, thus limiting the size of the relocatable contents of this image to 16 megabytes.

2009-02-04 | Copyright © 2003, 2009 Apple Inc. All Rights Reserved.

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