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(stabs.info)Procedures

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Procedures
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   All of the following stabs normally use the `N_FUN' symbol type.
However, Sun's `acc' compiler on SunOS4 uses `N_GSYM' and `N_STSYM',
which means that the value of the stab for the function is useless and
the debugger must get the address of the function from the non-stab
symbols instead.  On systems where non-stab symbols have leading
underscores, the stabs will lack underscores and the debugger needs to
know about the leading underscore to match up the stab and the non-stab
symbol.  BSD Fortran is said to use `N_FNAME' with the same
restriction; the value of the symbol is not useful (I'm not sure it
really does use this, because GDB doesn't handle this and no one has
complained).

   A function is represented by an `F' symbol descriptor for a global
(extern) function, and `f' for a static (local) function.  For a.out,
the value of the symbol is the address of the start of the function; it
is already relocated.  For stabs in ELF, the SunPRO compiler version
2.0.1 and GCC put out an address which gets relocated by the linker.
In a future release SunPRO is planning to put out zero, in which case
the address can be found from the ELF (non-stab) symbol.  Because
looking things up in the ELF symbols would probably be slow, I'm not
sure how to find which symbol of that name is the right one, and this
doesn't provide any way to deal with nested functions, it would
probably be better to make the value of the stab an address relative to
the start of the file, or just absolute.  See Note: ELF Linker
Relocation for more information on linker relocation of stabs in ELF
files.  For XCOFF, the stab uses the `C_FUN' storage class and the
value of the stab is meaningless; the address of the function can be
found from the csect symbol (XTY_LD/XMC_PR).

   The type information of the stab represents the return type of the
function; thus `foo:f5' means that foo is a function returning type 5.
There is no need to try to get the line number of the start of the
function from the stab for the function; it is in the next `N_SLINE'
symbol.

   Some compilers (such as Sun's Solaris compiler) support an extension
for specifying the types of the arguments.  I suspect this extension is
not used for old (non-prototyped) function definitions in C.  If the
extension is in use, the type information of the stab for the function
is followed by type information for each argument, with each argument
preceded by `;'.  An argument type of 0 means that additional arguments
are being passed, whose types and number may vary (`...' in ANSI C).
GDB has tolerated this extension (parsed the syntax, if not necessarily
used the information) since at least version 4.8; I don't know whether
all versions of dbx tolerate it.  The argument types given here are not
redundant with the symbols for the formal parameters (Note:
Parameters); they are the types of the arguments as they are passed,
before any conversions might take place.  For example, if a C function
which is declared without a prototype takes a `float' argument, the
value is passed as a `double' but then converted to a `float'.
Debuggers need to use the types given in the arguments when printing
values, but when calling the function they need to use the types given
in the symbol defining the function.

   If the return type and types of arguments of a function which is
defined in another source file are specified (i.e., a function
prototype in ANSI C), traditionally compilers emit no stab; the only
way for the debugger to find the information is if the source file
where the function is defined was also compiled with debugging symbols.
As an extension the Solaris compiler uses symbol descriptor `P'
followed by the return type of the function, followed by the arguments,
each preceded by `;', as in a stab with symbol descriptor `f' or `F'.
This use of symbol descriptor `P' can be distinguished from its use for
register parameters (Note: Register Parameters) by the fact that it
has symbol type `N_FUN'.

   The AIX documentation also defines symbol descriptor `J' as an
internal function.  I assume this means a function nested within another
function.  It also says symbol descriptor `m' is a module in Modula-2
or extended Pascal.

   Procedures (functions which do not return values) are represented as
functions returning the `void' type in C.  I don't see why this couldn't
be used for all languages (inventing a `void' type for this purpose if
necessary), but the AIX documentation defines `I', `P', and `Q' for
internal, global, and static procedures, respectively.  These symbol
descriptors are unusual in that they are not followed by type
information.

   The following example shows a stab for a function `main' which
returns type number `1'.  The `_main' specified for the value is a
reference to an assembler label which is used to fill in the start
address of the function.

     .stabs "main:F1",36,0,0,_main      # 36 is N_FUN

   The stab representing a procedure is located immediately following
the code of the procedure.  This stab is in turn directly followed by a
group of other stabs describing elements of the procedure.  These other
stabs describe the procedure's parameters, its block local variables,
and its block structure.

   If functions can appear in different sections, then the debugger may
not be able to find the end of a function.  Recent versions of GCC will
mark the end of a function with an `N_FUN' symbol with an empty string
for the name.  The value is the address of the end of the current
function.  Without such a symbol, there is no indication of the address
of the end of a function, and you must assume that it ended at the
starting address of the next function or at the end of the text section
for the program.