SPNU118Z September 1995 – March 2023 66AK2E05 , 66AK2H06 , 66AK2H12 , 66AK2H14 , AM1705 , AM1707 , AM1802 , AM1806 , AM1808 , AM1810 , AM5K2E04 , OMAP-L132 , OMAP-L137 , OMAP-L138 , SM470R1B1M-HT , TMS470R1A288 , TMS470R1A384 , TMS470R1A64 , TMS470R1B1M , TMS470R1B512 , TMS470R1B768
The assembler treats each section as if it began at address 0. Of course, all sections cannot actually begin at address 0 in memory, so the linker must relocate sections. Relocations are symbol-relative rather than section-relative.
The linker can relocate sections by:
The linker uses relocation entries to adjust references to symbol values. The assembler creates a relocation entry each time a relocatable symbol is referenced. The linker then uses these entries to patch the references after the symbols are relocated. The following example contains a code fragment for a ARM device for which the assembler generates relocation entries.
1 *********************************************
2 ** Generating Relocation Entries **
3 *********************************************
4 .ref X
5 .def Y
6 00000000 .text
7 00000000 E0921003 ADDS R1, R2, R3
8 00000004 0A000001 BEQ Y
9 00000008 E1C410BE STRH R1, [R4, #14]
10 0000000c EAFFFFFB! B X ; generates a relocation entry
11 00000010 E0821003 Y: ADD R1, R2, R3In the previous example, both symbols X and Y are relocatable. Y is defined in the .text section of this module; X is defined in another module. When the code is assembled, X has a value of 0 (the assembler assumes all undefined external symbols have values of 0), and Y has a value of 16 (relative to address 0 in the .text section). The assembler generates two relocation entries: one for X and one for Y. The reference to X is an external reference (indicated by the ! character in the listing). The reference to Y is to an internally defined relocatable symbol (indicated by the ' character in the listing).
After the code is linked, suppose that X is relocated to address 0x10014. Suppose also that the .text section is relocated to begin at address 0x10000; Y now has a relocated value of 0x10010. The linker uses the relocation entry for the reference to X to patch the branch instruction in the object code:
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