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Handling of Jump Instructions
Jump instructions are always optimized to use the smallest possible
displacements. This is accomplished by using byte (8-bit) displacement
jumps whenever the target is sufficiently close. If a byte displacement
is insufficient a long displacement is used. We do not support word
(16-bit) displacement jumps in 32-bit mode (i.e. prefixing the jump
instruction with the `data16' instruction prefix), since the 80386
insists upon masking `%eip' to 16 bits after the word displacement is
added. (See also *note i386-Arch::)
Note that the `jcxz', `jecxz', `loop', `loopz', `loope', `loopnz'
and `loopne' instructions only come in byte displacements, so that if
you use these instructions (`gcc' does not use them) you may get an
error message (and incorrect code). The AT&T 80386 assembler tries to
get around this problem by expanding `jcxz foo' to
jcxz cx_zero
jmp cx_nonzero
cx_zero: jmp foo
cx_nonzero:
Created Wed Sep 1 16:41:06 2004 on bee with info_to_html version 0.9.6.