ltrace.conf(5) — Linux manual page


ltrace.conf(5)          ltrace configuration file         ltrace.conf(5)

NAME         top

       ltrace.conf - Configuration file for ltrace(1).

DESCRIPTION         top

       This manual page describes ltrace.conf, a file that describes
       prototypes of functions in binaries for ltrace(1) to use.  Ltrace
       needs this information to display function call arguments.

       Each line of a configuration file describes at most a single
       item.  Lines composed entirely of white space are ignored, as are
       lines starting with semicolon or hash characters (comment lines).
       Described items can be either function prototypes, or definitions
       of type aliases.

PROTOTYPES         top

       A prototype describes return type and parameter types of a single
       function.  The syntax is as follows:

              [function] LENS NAME ([LENS{,LENS}]);

       NAME is the (mangled) name of a symbol.  In the elementary case,
       LENS is simply a type.  Both lenses and types are described
       below.  The function keyword, if present, has no effect.  It can
       be used to force a line to be interpreted as a function prototype
       when the return type is a keyword that would start a different
       type of line (such as import).

       For example, a simple function prototype might look like this:

              int kill(int,int);

       Despite the apparent similarity with C, ltrace.conf is really its
       own language that's only somewhat inspired by C.

TYPES         top

       Ltrace understands a range of primitive types.  Those are
       interpreted according to C convention native on a given
       architecture.  E.g. ulong is interpreted as 4-byte unsigned
       integer on 32-bit GNU/Linux machine, but 8-byte unsigned integer
       on 64-bit GNU/Linux machine.

       void   Denotes that a function does not return anything.  Can be
              also used to construct a generic pointer, i.e. pointer-
              sized number formatted in hexadecimal format.

       char   8-bit quantity rendered as a character

              Denotes unsigned or signed short integer.

              Denotes unsigned or signed integer.

              Denotes unsigned or signed long integer.

       float  Denotes floating point number with single precision.

       double Denotes floating point number with double precision.

       Besides primitive types, the following composed types are

              Describes a structure with given types as fields, e.g.

              Alignment is computed as customary on the architecture.
              Custom alignment (e.g. packed structs) and bit-fields are
              not supported.  It's also not possible to differentiate
              between structs and non-POD C++ classes, for arches where
              it makes a difference.

              Describes array of length EXPR, which is composed of types
              described by LENS, e.g. array(int, 6).

              Note that in C, arrays in role of function argument decay
              into pointers.  Ltrace currently handles this
              automatically, but for full formal correctness, any such
              arguments should be described as pointers to arrays.

       LENS*  Describes a pointer to a given type, e.g. char* or int***.
              Note that the former example actually describes a pointer
              to a character, not a string.  See below for string lens,
              which is applicable to these cases.

LENSES         top

       Lenses change the way that types are described.  In the simplest
       case, a lens is directly a type.  Otherwise a type is decorated
       by the lens.  Ltrace understands the following lenses:

              The argument, which should be an integer type, is
              formatted in base-8.

              The argument, which should be an integer or floating point
              type, is formatted in base-16.  Floating point arguments
              are converted to double and then displayed using the %a
              fprintf modifier.

              The argument is not shown in argument list.

              Arguments with zero value are shown as "false", others are
              shown as "true".

              Underlying argument is interpreted as a bit vector and a
              summary of bits set in the vector is displayed.  For
              example if bits 3,4,5 and 7 of the bit vector are set,
              ltrace shows <3-5,7>.  Empty bit vector is displayed as
              <>.  If there are more bits set than unset, inverse is
              shown instead: e.g. ~<0> when a number 0xfffffffe is
              displayed.  Full set is thus displayed ~<>.

              If the underlying type is integral, then bits are shown in
              their natural big-endian order, with LSB being bit 0.
              E.g. bitvec(ushort) with value 0x0102 would be displayed
              as <1,8>, irrespective of underlying byte order.

              For other data types (notably structures and arrays), the
              underlying data is interpreted byte after byte.  Bit 0 of
              first byte has number 0, bit 0 of second byte number 8,
              and so on.  Thus bitvec(struct(int)) is endian sensitive,
              and will show bytes comprising the integer in their memory
              order.  Pointers are first dereferenced, thus
              bitvec(array(char, 32)*) is actually a pointer to 256-bit
              bit vector.

              The first form of the argument is canonical, the latter
              two are syntactic sugar.  In the canonical form, the
              function argument is formatted as string.  The TYPE can
              have either of the following forms: X*, or array(X,EXPR),
              or array(X,EXPR)*.  X is either char for normal strings,
              or an integer type for wide-character strings.

              If an array is given, the length will typically be a zero
              expression (but doesn't have to be).  Using argument that
              is plain array (i.e. not a pointer to array) makes sense
              e.g. in C structs, in cases like struct(string(array(char,
              6))), which describes the C type struct {char s[6];}.

              Because simple C-like strings are pretty common, there are
              two shorthand forms.  The first shorthand form (with
              brackets) means the same as string(array(char, EXPR)*).
              Plain string without an argument is then taken to mean the
              same as string[zero].

              Note that char* by itself describes a pointer to a char.
              Ltrace will dereference the pointer, and read and display
              the single character that it points to.

              This describes an enumeration lens.  If an argument has
              any of the given values, it is instead shown as the
              corresponding NAME.  If a VALUE is omitted, the next
              consecutive value following after the previous VALUE is
              taken instead.  If the first VALUE is omitted, it's 0 by

              TYPE, if given, is the underlying type.  It is thus
              possible to create enums over shorts or longs—arguments
              that are themselves plain, non-enum types in C, but whose
              values can be meaningfully described as enumerations.  If
              omitted, TYPE is taken to be int.

TYPE ALIASES         top

       A line in config file can, instead of describing a prototype,
       create a type alias.  Instead of writing the same enum or struct
       on many places (and possibly updating when it changes), one can
       introduce a name for such type, and later just use that name:

              typedef NAME = LENS;


       It's possible for config files to import definitions from other
       config files.  A line of the form:

              import "FILENAME";

       will make all definitions from FILENAME.conf available in the
       current file.  The imported file is searched for in the same
       directories as when looking up a config file corresponding to a
       library; see ltrace(1) for details.


       Ltrace allows you to express recursive structures.  Such
       structures are expanded to the depth described by the parameter
       -A.  To declare a recursive type, you first have to introduce the
       type to ltrace by using forward declaration.  Then you can use
       the type in other type definitions in the usual way:

              typedef NAME = struct;
              typedef NAME = struct(NAME can be used here)

       For example, consider the following singy-linked structure and a
       function that takes such list as an argument:

              typedef int_list = struct;
              typedef int_list = struct(int, int_list*);
              void ll(int_list*);

       Such declarations might lead to an output like the following:

              ll({ 9, { 8, { 7, { 6, ... } } } }) = <void>

       Ltrace detects recursion and will not expand already-expanded
       structures.  Thus a doubly-linked list would look like the

              typedef int_list = struct;
              typedef int_list = struct(int, int_list*, int_list*);

       With output e.g. like:

              ll({ 9, { 8, { 7, { 6, ..., ... }, recurse^ }, recurse^ },
              nil })

       The "recurse^" tokens mean that given pointer points to a
       structure that was expanded in the previous layer.  Simple
       "recurse" would mean that it points back to this object.  E.g.
       "recurse^^^" means it points to a structure three layers up.  For
       doubly-linked list, the pointer to the previous element is of
       course the one that has been just expanded in the previous round,
       and therefore all of them are either recurse^, or nil.  If the
       next and previous pointers are swapped, the output adjusts

              ll({ 9, nil, { 8, recurse^, { 7, recurse^, { 6, ..., ... }
              } } })

EXPRESSIONS         top

       Ltrace has support for some elementary expressions.  Each
       expression can be either of the following:

       NUM    An integer number.

       argNUM Value of NUM-th argument.  The expression has the same
              value as the corresponding argument.  arg1 refers to the
              first argument, arg0 to the return value of the given

       retval Return value of function, same as arg0.

       eltNUM Value of NUM-th element of the surrounding structure type.
              E.g.  struct(ulong,array(int,elt1)) describes a structure
              whose first element is a length, and second element an
              array of ints of that length.

              Describes array which extends until the first element,
              whose each byte is 0.  If an expression is given, that is
              the maximum length of the array.  If NUL terminator is not
              found earlier, that's where the array ends.


       Sometimes the actual function prototype varies slightly depending
       on the exact parameters given.  For example, the number and types
       of printf parameters are not known in advance, but ltrace might
       be able to determine them in runtime.  This feature has wider
       applicability, but currently the only parameter pack that ltrace
       supports is printf-style format string itself:

       format When format is seen in the parameter list, the underlying
              string argument is parsed, and GNU-style format specifiers
              are used to determine what the following actual arguments
              are.  E.g. if the format string is "%s %d\n", it's as if
              the format was replaced by string, string, int.


       C functions often use one or more arguments for returning values
       back to the caller.  The caller provides a pointer to storage,
       which the called function initializes.  Ltrace has some support
       for this idiom.

       When a traced binary hits a function call, ltrace first fetches
       all arguments.  It then displays left portion of the argument
       list.  Only when the function returns does ltrace display right
       portion as well.  Typically, left portion takes up all the
       arguments, and right portion only contains return value.  But
       ltrace allows you to configure where exactly to put the dividing
       line by means of a + operator placed in front of an argument:

              int asprintf(+string*, format);

       Here, the first argument to asprintf is denoted as return
       argument, which means that displaying the whole argument list is
       delayed until the function returns:

              a.out->asprintf( <unfinished ...>
    >malloc(100)                   = 0x245b010
              [... more calls here ...]
              <... asprintf resumed> "X=1", "X=%d", 1) = 5

       It is currently not possible to have an "inout" argument that
       passes information in both directions.

EXAMPLES         top

       In the following, the first is the C prototype, and following
       that is ltrace configuration line.

       void func_charp_string(char str[]);
              void func_charp_string(string);

       enum e_foo {RED, GREEN, BLUE};
       void func_enum(enum e_foo bar);
              void func_enum(enum(RED,GREEN,BLUE));
                     - or -
              typedef e_foo = enum(RED,GREEN,BLUE);
              void func_enum(e_foo);

       void func_arrayi(int arr[], int len);
              void func_arrayi(array(int,arg2)*,int);

       struct S1 {float f; char a; char b;};
       struct S2 {char str[6]; float f;};
       struct S1 func_struct(int a, struct S2, double d);
              struct(float,char,char) func_struct(int,
              struct(string(array(char, 6)),float), double);

AUTHOR         top

       Petr Machata <>

COLOPHON         top

       This page is part of the ltrace (library call tracer) project.
       Information about the project can be found at 
       ⟨⟩.  If you have a bug report for this manual
       page, see ⟨⟩.  This page was obtained from the
       project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-07-05.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

                              October 2012                ltrace.conf(5)

Pages that refer to this page: ltrace(1)