x86: Local Executable (LE)

This code sequence can only be used from within a dynamic executable and referencing a TLS variable defined within the executable. If this is the case the static tlsoffset it known at link-edit time and no runtime relocations are required.

0x00 movl %gs:0, %eax
0x06 leal x@ntpoff(%eax), %eax

# %eax - contains address of TLS variable

<none>
R_386_TLS_LE

 
x

The movl instruction generates aR_386_TLS_LE_32 relocation. The link-editor binds this relocation directly to the static TLS offset for the symbol defined in the executable. No processing is required at runtime.

The contents of variable x, rather then the address, can be accessed with the same relocation by using the following instruction sequence.

0x00 movl %gs:0, %eax
0x06 movl x@ntpoff(%eax), %eax

# %eax - contains address of TLS variable

<none>
R_386_TLS_LE

 
x

If instead of computing the address of the variable we want to load from it or store in it the following sequence can be used. Note that in this case we use the x@ntpoff expression not as an immediate value, but instead as an absolute address.

0x00 movl %gs:x@ntpoff, %eax

# %eax - contains address of TLS variable

R_386_TLS_LE

x