Linker and Libraries Guide

x64: Initial Executable (IE)

This code sequence implements the IE model described in Thread-Local Storage Access Models.

Table 8–20 x64: Initial Executable, Thread-Local Variable Access Codes


Code Sequence	Initial Relocations	Symbol
0x00 movq %fs:0, %rax 0x09 addq x@gottpoff(%rip), %rax # %rax - contains address of TLS variable	<none> R_AMD64_GOTTPOFF	x
	Outstanding Relocations	Symbol
GOT[n]	R_AMD64_TPOFF64	x

The R_AMD64_GOTTPOFF relocation for the symbol x requests the link-editor to generate a GOT entry and an associated R_AMD64_TPOFF64 relocation. The offset of the GOT entry relative to the end of the x@gottpoff(%rip) instruction, is then used by the instruction. The R_AMD64_TPOFF64 relocation uses the value of the symbol x that is determined from the presently loaded modules. The offset is written in the GOT entry and later loaded by the addq instruction.

To load the contents of x, rather than the address of x, the following sequence is available.

Table 8–21 x64: Initial Executable, Thread-Local Variable Access Codes II


Code Sequence	Initial Relocations	Symbol
0x00 movq x@gottpoff(%rip), %rax 0x06 movq %fs:(%rax), %rax # %rax - contains contents of TLS variable	R_AMD64_GOTTPOFF <none>	x
	Outstanding Relocations	Symbol
GOT[n]	R_AMD64_TPOFF64	x