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| -rw-r--r-- | src/BNF | 151 |
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@@ -0,0 +1,151 @@ +This is a first attempt to document the grammar used by magic(5), with +hopes of eventually incorporating something like this into the manpage. + +Note: Currently, the parser varies slightly from this, but only in +very minor ways, e.g., the strflags maybe separated by '/' characters +and at most one strcount is allowed; likewise for regflags. + +------------------------------------------------------------------------ +magic = 1*query + +query = line *( 1*level line ) + +level = ">" ;; Increment the level by 1. + ;; The first line of a query is at level 0. + +line = offset HWS type HWS test HWS message EOL + +------------------------------------------------------------------------ +offset = absoffset | reloffset | indoffset + ;; The offset in the file at which to apply + ;; the <test>. + +absoffset = NUMBER ;; An absolute offset from the start of the file. + +reloffset = "&" NUMBER ;; The offset relative to the last match offset + ;; at one level up. + ;; Not allowed at level == 0. + +indoffset = indoff | relindoff + +indoff = "(" offset1 [ "." size ] [ op disp ] ")" + ;; Read the file at <offset1> of width <size>. + ;; If size is not specified, assume a long. + ;; If <op> is given, then preform that + ;; operation on the result and the <disp>. + +offset1 = absoffset | reloffset + +size = byte | leshort | beshort | lelong | belong | melong + +byte = "B" | "b" | "C" | "c" ;; A one-byte value. +leshort = "s" | "h" ;; A two-byte little-endian value. +beshort = "S" | "H" ;; A two-byte big-endian value. +lelong = "l" ;; A four-byte little-endian value. +belong = "L" ;; A four-byte big-endian value. +melong = "m" ;; A four-byte middle-endian value. + +op = [ invert ] ( "+" | "-" | "*" | "/" | "%" | "&" | "|" | "^" ) + +invert = "~" ;; Flip the bits on result of the <op>. + +disp = NUMBER | memvalue + +memvalue = "(" NUMBER ")" + ;; NUMBER is interpreted as an absolute or + ;; relative offset matching that of <offset1>. + ;; Read the file at the resulting offset with + ;; the same size as <offset1> + +relindoff = "&" indoff ;; add <indoff> to the last match offset at + ;; one level up. + +------------------------------------------------------------------------ +type = [ unsigned ] ( numeric | strtype | default ) + +unsigned = "u" ;; The value is unsigned. + ;; This affects the sign extension of numeric + ;; types and the '<' and '>' compares. It is + ;; intended for numeric types, but allowed on + ;; all types. + +numeric = ( numtype | datatype ) [ nummask ] + +numtype = byte | short | long | quad + +byte = "byte" +short = "short" | "beshort" | "leshort" +long = "long" | "lelong" | "belong" | "melong" +quad = "quad" | "lequad" | "bequad" + +datetype = udate32 | ldate32 | udate64 | ldate64 + +udate32 = "date" | "bedate" | "ledate" | "medate" ;; UTC dates +ldate32 = "ldate" | "beldate" | "leldate" | "meldate" ;; local dates +udate64 = "qdate" | "leqdate" | "beqdate" ;; UTC dates +ldate64 = "qldate" | "leqldate" | "beqldate" ;; local dates + +nummask = op NUMBER + +strtype = regex | search | string8 | string16 + +regex = "regex" [ "/" 1*regflag ] + +regflag = "c" | "s" | linecnt + +linecnt = NUMBER ;; The number of lines to search. If this + ;; is missing or zero, the rest of the + ;; file is searched. + +search = "string" [ "/" 1*srchflag ] + +srchflag = strflag | srchcnt + +srchcnt = NUMBER ;; The number of search tries. If this + ;; is missing or zero, the rest of the + ;; file is searched. + +string8 = ( "string" | "pstring" ) [ "/" 1*strflag ] + +strflag = "b" | "B" | "c" | "C" + +string16 = "bestring16" | "lestring16" + +default = "default" ;; This is intended to be used with the + ;; <truetest> ("x" below). It is matched if + ;; there has been no previous match at its + ;; level or none since the last default at + ;; that level. It is useful for implementing + ;; switch-like and if/else constructions. + +------------------------------------------------------------------------ +test = numtest | strtest | truetest + ;; Test to preform on <type> read from file. + +numtest = [ compare ] NUMBER ;; If compare is missing, "=" is assumed. + +strtest = [ compare ] STRING ;; If compare is missing, "=" is assumed. + ;; Note: If the STRING begins with a <compare> + ;; character, the <compare> field cannot be + ;; omitted. + +compare = "=" | "!" | "<" | ">" | "&" | "^" + +truetest = "x" ;; This always returns true. + ;; To test for the string "x" use "=x". + +------------------------------------------------------------------------ +message = [ nospflag ] ( STRING | FMT_STRING ) + ;; Message to print if test result is true. + +nospflag = %x08 | "\\b" ;; Do not insert a space before the message. + ;; By default, messages are separated by a " ". + +------------------------------------------------------------------------ +HWS = <horizontal white space> +EOL = <end of line marker> +NUMBER = <C-style unsigned number> +STRING = <C-style string without delimiting quotes> +FMTSTR = <printf format string with exactly one % construct> + +------------------------------------------------------------------------ |