Provided by: ltrace_0.7.3-6.1ubuntu1_amd64 bug

NAME

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

DESCRIPTION

       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  character
       (comment  lines).   Described  items  can be either function prototypes, or definitions of
       type aliases.

PROTOTYPES

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

              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.  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

       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

       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
              shall be either a char*, or array(char,EXPR), or array(char,EXPR)*.  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

       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;

RECURSIVE STRUCTURES

       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

       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

       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

       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

       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_2(int,  struct(string(array(char,  6)),float),
              double);

AUTHOR

       Petr Machata <pmachata@redhat.com>

                                           October 2012                            ltrace.conf(5)