mirror/nasm
2
0
Fork 0
mirror of https://github.com/netwide-assembler/nasm.git synced 2025-04-18 18:50:23 +08:00
Code Issues Packages Projects Releases Wiki Activity

doc: document long-standing restrictions in the use of $ in Dx

Browse Source 
$ in data expressions is hazardous. A proper fix for this turns out to
be quite complex, as it requires the expression engine to propagate
additional data. For now, just put it into the documentation.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin (Intel) 2020-08-17 15:10:26 -07:00
parent 8806c3ca00
commit 235a115130
2 changed files with 27 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
doc/changes.src
View File

@ -34,11 +34,8 @@ operation size (e.g. \c{movsd qword [eax],xmm0}).
\b The \c{-L+} option no longer enables \c{-Lw}, which is mainly
useful to debug NASM crashes. See \k{opt-L}.
\b Fix the \c{__float80e__} and \c{__float128h__} conversions, which
would return the wrong bytes of the result.
\b Fix inefficient encoding of the \c{BNDMK}, \c{BNDLDX}, and
\c{BNDSTX} instructions under certain circumstances.
\b Document long-standing hazards in the use of \c{$} in \c{Dx}
statements, see \k{db}.
\S{cl-2.15.03} Version 2.15.03

30
doc/nasmdoc.src
View File

@ -1259,12 +1259,16 @@ uninitialized}\i{uninitialized} counterparts \i\c{RESB}, \i\c{RESW},
\i\c\{RESZ}; the \i\c{INCBIN} command, the \i\c{EQU} command, and the
\i\c{TIMES} prefix.
In this documentation, the notation "\c{Dx}" and "\c{RESx}" is used to
indicate all the \c{DB} and \c{RESB} type directives, respectively.
\S{db} \c{DB} and Friends: Declaring Initialized Data
\S{db} \c{Dx}: Declaring Initialized Data
\i\c{DB}, \i\c{DW}, \i\c{DD}, \i\c{DQ}, \i\c{DT}, \i\c{DO}, \i\c{DY}
and \i\c{DZ} are used, much as in MASM, to declare initialized data in
the output file. They can be invoked in a wide range of ways:
and \i\c{DZ} (collectively "\c{Dx}" in this documentation) are used,
much as in MASM, to declare initialized data in the output file. They
can be invoked in a wide range of ways:
\I{floating-point}\I{character constant}\I{string constant}
\c db 0x55 ; just the byte 0x55
@ -1281,8 +1285,8 @@ the output file. They can be invoked in a wide range of ways:
\c dq 1.234567e20 ; double-precision float
\c dt 1.234567e20 ; extended-precision float
\c{DT}, \c{DO}, \c{DY} and \c{DZ} do not accept \i{numeric constants}
as operands.
\c{DT}, \c{DO}, \c{DY} and \c{DZ} do not accept integer
\i{numeric constants} as operands.
\I{masmdb} Starting in NASM 2.15, a the following \i{MASM}-like features
have been implemented:
@ -1328,6 +1332,22 @@ valid:
\c dd 16 dup (0xaaaa, ?, 0xbbbbbb)
\c dd 64 dup (?)
\I{baddb} The use of \c{$} (current address) in a \c{Dx} statement is
undefined in the current version of NASM, \e{except in the following
cases}:
\b For the first expression in the statement, either a \c{DUP} or a data
item.
\b An expression of the form "\e{value}\c{ - $}", which is converted
to a self-relative relocation.
Future versions of NASM is likely to produce a different result or
issue an error this case.
There is no such restriction on using \c{$$} or section-relative
symbols.
\S{resb} \c{RESB} and Friends: Declaring \i{Uninitialized} Data
\i\c{RESB}, \i\c{RESW}, \i\c{RESD}, \i\c{RESQ}, \i\c{REST},