2 .\" Copyright (c) 2012 Petr Machata, Red Hat Inc.
3 .\" Copyright (c) 1997-2005 Juan Cespedes <cespedes@debian.org>
5 .\" This program is free software; you can redistribute it and/or
6 .\" modify it under the terms of the GNU General Public License as
7 .\" published by the Free Software Foundation; either version 2 of the
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11 .\" WITHOUT ANY WARRANTY; without even the implied warranty of
12 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 .\" General Public License for more details.
15 .\" You should have received a copy of the GNU General Public License
16 .\" along with this program; if not, write to the Free Software
17 .\" Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
20 .TH ltrace.conf "5" "October 2012" "" "ltrace configuration file"
23 \fBltrace.conf\fR \- Configuration file for \fBltrace(1)\fR.
27 This manual page describes \fBltrace.conf\fR, a file that describes
28 prototypes of functions in binaries for \fBltrace(1)\fR to use.
29 Ltrace needs this information to display function call arguments.
31 Each line of a configuration file describes at most a single item.
32 Lines composed entirely of white space are ignored, as are lines
33 starting with semicolon character (comment lines). Described items
34 can be either function prototypes, or definitions of type aliases.
38 A prototype describes return type and parameter types of a single
39 function. The syntax is as follows:
42 \fILENS\fR \fINAME\fR \fB(\fR[\fILENS\fR{,\fILENS\fR}]\fB);\fR
45 \fINAME\fR is the (mangled) name of a symbol. In the elementary case,
46 \fILENS\fR is simply a type. Both lenses and types are described
47 below. For example, a simple function prototype might look like this:
50 .B int\fR kill\fB(int,int);
53 Despite the apparent similarity with C, \fBltrace.conf\fR is really
54 its own language that's only somewhat inspired by C.
58 Ltrace understands a range of primitive types. Those are interpreted
59 according to C convention native on a given architecture.
60 E.g. \fBulong\fR is interpreted as 4-byte unsigned integer on 32-bit
61 GNU/Linux machine, but 8-byte unsigned integer on 64-bit GNU/Linux
66 Denotes that a function does not return anything. Can be also used to
67 construct a generic pointer, i.e. pointer-sized number formatted in
71 8-bit quantity rendered as a character
74 Denotes unsigned or signed short integer.
77 Denotes unsigned or signed integer.
80 Denotes unsigned or signed long integer.
83 Denotes floating point number with single precision.
86 Denotes floating point number with double precision.
89 Besides primitive types, the following composed types are possible:
92 .B struct(\fR[\fILENS\fR{,\fILENS\fR}]\fB)\fR
93 Describes a structure with given types as fields,
94 e.g. \fBstruct(int,int,float)\fR.
96 Alignment is computed as customary on the architecture. Custom
97 alignment (e.g. packed structs) and bit-fields are not supported.
98 It's also not possible to differentiate between structs and non-POD
99 C++ classes, for arches where it makes a difference.
102 .B array(\fR\fILENS\fR\fB,\fIEXPR\fR\fB)
103 Describes array of length \fIEXPR\fR, which is composed of types
104 described by \fILENS\fR, e.g. \fBarray(int, \fR6\fB)\fR.
106 Note that in C, arrays in role of function argument decay into
107 pointers. Ltrace currently handles this automatically, but for full
108 formal correctness, any such arguments should be described as pointers
113 Describes a pointer to a given type, e.g. \fBchar*\fR or \fBint***\fR.
114 Note that the former example actually describes a pointer to a
115 character, not a string. See below for \fBstring\fR lens, which is
116 applicable to these cases.
120 Lenses change the way that types are described. In the simplest case,
121 a lens is directly a type. Otherwise a type is decorated by the lens.
122 Ltrace understands the following lenses:
126 The argument, which should be an integer type, is formatted in base-8.
130 The argument, which should be an integer or floating point type, is
131 formatted in base-16. Floating point arguments are converted to
132 double and then displayed using the \fB%a\fR fprintf modifier.
136 The argument is not shown in argument list.
140 Arguments with zero value are shown as "false", others are shown as
144 .B bitvec(\fITYPE\fB)
145 Underlying argument is interpreted as a bit vector and a summary of
146 bits set in the vector is displayed. For example if bits 3,4,5 and 7
147 of the bit vector are set, ltrace shows <3-5,7>. Empty bit vector is
148 displayed as <>. If there are more bits set than unset, inverse is
149 shown instead: e.g. ~<0> when a number 0xfffffffe is displayed. Full
150 set is thus displayed ~<>.
152 If the underlying type is integral, then bits are shown in their
153 natural big-endian order, with LSB being bit 0.
154 E.g. \fBbitvec(ushort)\fR with value 0x0102 would be displayed as
155 <1,8>, irrespective of underlying byte order.
157 For other data types (notably structures and arrays), the underlying
158 data is interpreted byte after byte. Bit 0 of first byte has number
159 0, bit 0 of second byte number 8, and so on. Thus
160 \fBbitvec(struct(int))\fR is endian sensitive, and will show bytes
161 comprising the integer in their memory order. Pointers are first
162 dereferenced, thus \fBbitvec(array(char, \fR32\fB)*)\fR is actually a
163 pointer to 256-bit bit vector.
166 .B string(\fITYPE\fB)
168 .B string[\fIEXPR\fB]
172 The first form of the argument is canonical, the latter two are
173 syntactic sugar. In the canonical form, the function argument is
174 formatted as string. The \fITYPE\fR shall be either a \fBchar*\fR, or
175 \fBarray(char,\fIEXPR\fB)\fR, or \fBarray(char,\fIEXPR\fB)*\fR. If an
176 array is given, the length will typically be a \fBzero\fR expression
177 (but doesn't have to be). Using argument that is plain array
178 (i.e. not a pointer to array) makes sense e.g. in C structs, in cases
179 like \fBstruct(string(array(char, \fR6\fB)))\fR, which describes the C
180 type \fBstruct {char \fRs\fB[\fR6\fB];}\fR.
182 Because simple C-like strings are pretty common, there are two
183 shorthand forms. The first shorthand form (with brackets) means the
184 same as \fBstring(array(char, \fIEXPR\fB)*)\fR. Plain \fBstring\fR
185 without an argument is then taken to mean the same as
188 Note that \fBchar*\fR by itself describes a pointer to a char. Ltrace
189 will dereference the pointer, and read and display the single
190 character that it points to.
193 .B enum(\fINAME\fR[\fB=\fIVALUE\fR]{,\fINAME\fR[\fB=\fIVALUE\fR]}\fB)
195 .B enum[\fITYPE\fB]\fB(\fINAME\fR[\fB=\fIVALUE\fR]{,\fINAME\fR[\fB=\fIVALUE\fR]}\fB)
197 This describes an enumeration lens. If an argument has any of the
198 given values, it is instead shown as the corresponding \fINAME\fR. If
199 a \fIVALUE\fR is omitted, the next consecutive value following after
200 the previous \fIVALUE\fR is taken instead. If the first \fIVALUE\fR
201 is omitted, it's \fB0\fR by default.
203 \fITYPE\fR, if given, is the underlying type. It is thus possible to
204 create enums over shorts or longs\(emarguments that are themselves
205 plain, non-enum types in C, but whose values can be meaningfully
206 described as enumerations. If omitted, \fITYPE\fR is taken to be
212 A line in config file can, instead of describing a prototype, create a
213 type alias. Instead of writing the same enum or struct on many places
214 (and possibly updating when it changes), one can introduce a name for
215 such type, and later just use that name:
218 \fBtypedef \fINAME\fB = \fILENS\fB;\fR
221 .SH RECURSIVE STRUCTURES
223 Ltrace allows you to express recursive structures. Such structures
224 are expanded to the depth described by the parameter -A. To declare a
225 recursive type, you first have to introduce the type to ltrace by
226 using forward declaration. Then you can use the type in other type
227 definitions in the usual way:
230 .B typedef \fINAME\fB = struct;
232 .B typedef \fINAME\fB = struct(\fINAME\fR can be used here\fB)
235 For example, consider the following singy-linked structure and a
236 function that takes such list as an argument:
239 .B typedef\fR int_list \fB= struct;
241 .B typedef\fR int_list \fB= struct(int,\fR int_list\fB*);
243 .B void\fR ll\fB(\fRint_list\fB*);
246 Such declarations might lead to an output like the following:
249 ll({ 9, { 8, { 7, { 6, ... } } } }) = <void>
252 Ltrace detects recursion and will not expand already-expanded
253 structures. Thus a doubly-linked list would look like the following:
256 .B typedef\fR int_list \fB= struct;
258 .B typedef\fR int_list \fB= struct(int,\fR int_list\fB*,\fR int_list\fB*);
261 With output e.g. like:
264 ll({ 9, { 8, { 7, { 6, ..., ... }, recurse^ }, recurse^ }, nil })
267 The "recurse^" tokens mean that given pointer points to a structure
268 that was expanded in the previous layer. Simple "recurse" would mean
269 that it points back to this object. E.g. "recurse^^^" means it points
270 to a structure three layers up. For doubly-linked list, the pointer
271 to the previous element is of course the one that has been just
272 expanded in the previous round, and therefore all of them are either
273 recurse^, or nil. If the next and previous pointers are swapped, the
274 output adjusts correspondingly:
277 ll({ 9, nil, { 8, recurse^, { 7, recurse^, { 6, ..., ... } } } })
283 Ltrace has support for some elementary expressions. Each expression
284 can be either of the following:
292 Value of \fINUM\fR-th argument. The expression has the same value as
293 the corresponding argument. \fBarg1\fR refers to the first argument,
294 \fBarg0\fR to the return value of the given function.
298 Return value of function, same as \fBarg0\fR.
302 Value of \fINUM\fR-th element of the surrounding structure type. E.g.
303 \fBstruct(ulong,array(int,elt1))\fR describes a structure whose first
304 element is a length, and second element an array of ints of that
312 Describes array which extends until the first element, whose each byte
313 is 0. If an expression is given, that is the maximum length of the
314 array. If NUL terminator is not found earlier, that's where the array
320 Sometimes the actual function prototype varies slightly depending on
321 the exact parameters given. For example, the number and types of
322 printf parameters are not known in advance, but ltrace might be able
323 to determine them in runtime. This feature has wider applicability,
324 but currently the only parameter pack that ltrace supports is
325 printf-style format string itself:
329 When \fBformat\fR is seen in the parameter list, the underlying string
330 argument is parsed, and GNU-style format specifiers are used to
331 determine what the following actual arguments are. E.g. if the format
332 string is "%s %d\\n", it's as if the \fBformat\fR was replaced by
333 \fBstring, string, int\fR.
337 C functions often use one or more arguments for returning values back
338 to the caller. The caller provides a pointer to storage, which the
339 called function initializes. Ltrace has some support for this idiom.
341 When a traced binary hits a function call, ltrace first fetches all
342 arguments. It then displays \fIleft\fR portion of the argument list.
343 Only when the function returns does ltrace display \fIright\fR portion
344 as well. Typically, left portion takes up all the arguments, and
345 right portion only contains return value. But ltrace allows you to
346 configure where exactly to put the dividing line by means of a \fB+\fR
347 operator placed in front of an argument:
350 .B int\fR asprintf\fB(+string*, format);
353 Here, the first argument to asprintf is denoted as return argument,
354 which means that displaying the whole argument list is delayed until
355 the function returns:
358 a.out->asprintf( <unfinished ...>
360 libc.so.6->malloc(100) = 0x245b010
362 [... more calls here ...]
364 <... asprintf resumed> "X=1", "X=%d", 1) = 5
367 It is currently not possible to have an "inout" argument that passes
368 information in both directions.
372 In the following, the first is the C prototype, and following that is
373 ltrace configuration line.
376 .B void\fR func_charp_string\fB(char\fR str\fB[]);
377 .B void\fR func_charp_string\fB(string);
380 .B enum\fR e_foo \fB{\fRRED\fB, \fRGREEN\fB, \fRBLUE\fB};
382 .B void\fR func_enum\fB(enum\fR e_foo bar\fB);\fR
384 .B void\fR func_enum\fB(enum(\fRRED\fB,\fRGREEN\fB,\fRBLUE\fB));\fR
388 .B typedef\fR e_foo \fB= enum(\fRRED\fB,\fRGREEN\fB,\fRBLUE\fB);\fR
390 .B void\fR func_enum\fB(\fRe_foo\fB);\fR
394 .B void\fR func_arrayi\fB(int\fR arr\fB[],\fR int len\fB);
395 .B void\fR func_arrayi\fB(array(int,arg2)*,int);
398 .B struct\fR S1 \fB{float\fR f\fB; char\fR a\fB; char \fRb\fB;};
400 .B struct\fR S2 \fB{char\fR str\fB[\fR6\fB]; float\fR f\fB;};
402 .B struct\fR S1 func_struct\fB(int \fRa\fB, struct \fRS2\fB, double \fRd\fB);
404 .B struct(float,char,char)\fR func_struct_2\fB(int, struct(string(array(char, \fR6\fB)),float), double);
408 Petr Machata <pmachata@redhat.com>