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Document %use smartalign

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H. Peter Anvin 2008-09-03 15:03:20 -07:00
parent 4a532bc707
commit 39e9a5f72f
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doc/nasmdoc.src
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@ -197,6 +197,7 @@ Object File Format
\IR{shift command} \c{shift} command
\IA{sib}{sib byte}
\IR{sib byte} SIB byte
\IR{align, smart} \c{ALIGN}, smart
\IR{solaris x86} Solaris x86
\IA{standard section names}{standardized section names}
\IR{symbols, exporting from dlls} symbols, exporting from DLLs
@ -3868,6 +3869,8 @@ boundary, for example, is a waste of effort. Again, NASM does not
check that the section's alignment characteristics are sensible for
the use of \c{ALIGN} or \c{ALIGNB}.
See also the \c{smartalign} standard macro package, \k{pkg_smartalign}.
\C{macropkg} \i{Standard Macro Packages}
@ -3900,6 +3903,48 @@ Example use:
See also \k{reg64}.
\H{pkg_smartalign} \i\c{smartalign}\I{align, smart}: Smart \c{ALIGN} Macro
The \c{smartalign} standard macro package provides for an \i\c{ALIGN}
macro which is more powerful than the default (and
backwards-compatible) one (see \k{align}). When the \c{smartalign}
package is enabled, when \c{ALIGN} is used without a second argument,
NASM will generate a sequence of instructions more efficient than a
series of \c{NOP}. Furthermore, if the padding exceeds a specific
threshold, then NASM will generate a jump over the entire padding
sequence.
The specific instructions generated can be controlled with the
new \i\c{ALIGNMODE} macro. This macro takes two parameters: one mode,
and an optional jump threshold override. The modes are as
follows:
\b \c{generic}: Works on all x86 CPUs and should have reasonable
performance. The default jump threshold is 8. This is the
default.
\b \c{nop}: Pad out with \c{NOP} instructions. The only difference
compared to the standard \c{ALIGN} macro is that NASM can still jump
over a large padding area. The default jump threshold is 16.
\b \c{k7}: Optimize for the AMD K7 (Athlon/Althon XP). These
instructions should still work on all x86 CPUs. The default jump
threshold is 16.
\b \c{k8}: Optimize for the AMD K8 (Opteron/Althon 64). These
instructions should still work on all x86 CPUs. The default jump
threshold is 16.
\b \c{p6}: Optimize for Intel CPUs. This uses the long \c{NOP}
instructions first introduced in Pentium Pro. This is incompatible
with all CPUs of family 5 or lower, as well as some VIA CPUs and
several virtualization solutions. The default jump threshold is 16.
The macro \i\c{__ALIGNMODE__} is defined to contain the current
alignment mode. A number of other macros beginning with \c{__ALIGN_}
are used internally by this macro package.
\C{directive} \i{Assembler Directives}
NASM, though it attempts to avoid the bureaucracy of assemblers like