NAME | DESCRIPTION | PROTOTYPES | TYPES | LENSES | TYPE ALIASES | IMPORT DIRECTIVES | RECURSIVE STRUCTURES | EXPRESSIONS | PARAMETER PACKS | RETURN ARGUMENTS | EXAMPLES | AUTHOR | COLOPHON

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

       ushort,short
              Denotes unsigned or signed short integer.

       uint,int
              Denotes unsigned or signed integer.

       ulong,long
              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 possible:

       struct([LENS{,LENS}])
              Describes a structure with given types as fields, e.g.
              struct(int,int,float).

              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.

       array(LENS,EXPR)
              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:

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

       hex(TYPE)
              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.

       hide(TYPE)
              The argument is not shown in argument list.

       bool(TYPE)
              Arguments with zero value are shown as "false", others are
              shown as "true".

       bitvec(TYPE)
              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.

       string(TYPE)
       string[EXPR]
       string
              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.

       enum(NAME[=VALUE]{,NAME[=VALUE]})
       enum[TYPE](NAME[=VALUE]{,NAME[=VALUE]})
              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 default.

              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;

IMPORT DIRECTIVES         top

       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.

RECURSIVE STRUCTURES         top

       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 following:

              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 correspondingly:

              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 function.

       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.

       zero
       zero(EXPR)
              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.

PARAMETER PACKS         top

       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.

RETURN ARGUMENTS         top

       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 ...>
              libc.so.6->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 <pmachata@redhat.com>

COLOPHON         top

       This page is part of the ltrace (library call tracer) project.
       Information about the project can be found at ⟨http://ltrace.org/⟩.
       If you have a bug report for this manual page, see 
       ⟨http://ltrace.org/⟩.  This page was obtained from the project's
       upstream Git repository 
       ⟨git://anonscm.debian.org/collab-maint/ltrace.git⟩ on 2017-04-25.  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 man-pages@man7.org

                                October 2012                  ltrace.conf(5)

Pages that refer to this page: ltrace(1)