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vacall - C functions called with variable arguments
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##iinncclluuddee <<vvaaccaallll..hh>>
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eexxtteerrnn vvooiidd** vvaaccaallll__ffuunnccttiioonn;;
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vvooiidd _f_u_n_c_t_i_o_n ((_a_l_i_s_t))
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vvaa__aalliisstt _a_l_i_s_t;;
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vvaa__ssttaarrtt___t_y_p_e((_a_l_i_s_t[[,, _r_e_t_u_r_n___t_y_p_e]]));;
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_a_r_g == vvaa__aarrgg___t_y_p_e((_a_l_i_s_t[[,, _a_r_g___t_y_p_e]]));;
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vvaa__rreettuurrnn___t_y_p_e((_a_l_i_s_t[[[[,, _r_e_t_u_r_n___t_y_p_e]],, _r_e_t_u_r_n___v_a_l_u_e]]));;
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vvaaccaallll__ffuunnccttiioonn == _&_f_u_n_c_t_i_o_n;;
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_v_a_l == ((((_r_e_t_u_r_n___t_y_p_e ((**)) (()))) vvaaccaallll)) ((_a_r_g_1,,_a_r_g_2,,_._._.));;
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DDEESSCCRRIIPPTTIIOONN
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This set of macros permit a C function _f_u_n_c_t_i_o_n to be
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called with variable arguments and to return variable
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return values. This is much like the vvaarraarrggss(3) facility,
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but also allows the return value to be specified at run
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Function calling conventions differ considerably on dif-
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ferent machines, and _v_a_c_a_l_l attempts to provide some
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degree of isolation from such architecture dependencies.
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The function that can be called with any number and type
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of arguments and which will return any type of return
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value is vvaaccaallll. It will do some magic and call the func-
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tion stored in the variable vvaaccaallll__ffuunnccttiioonn. If you want
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to make more than one use of _v_a_c_a_l_l, use the _t_r_a_m_p_o_l_i_n_e(3)
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facility to store _&_f_u_n_c_t_i_o_n into vvaaccaallll__ffuunnccttiioonn just
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before calling vvaaccaallll.
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Within _f_u_n_c_t_i_o_n, the following macros can be used to walk
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through the argument list and specify a return value:
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vvaa__ssttaarrtt___t_y_p_e((_a_l_i_s_t[[,, _r_e_t_u_r_n___t_y_p_e]]));;
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starts the walk through the argument list and spec-
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ifies the return type.
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_a_r_g == vvaa__aarrgg___t_y_p_e((_a_l_i_s_t[[,, _a_r_g___t_y_p_e]]));;
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fetches the next argument from the argument list.
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vvaa__rreettuurrnn___t_y_p_e((_a_l_i_s_t[[[[,, _r_e_t_u_r_n___t_y_p_e]],, _r_e_t_u_r_n___v_a_l_u_e]]));;
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ends the walk through the argument list and speci-
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fies the return value.
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The _t_y_p_e in vvaa__ssttaarrtt___t_y_p_e and vvaa__rreettuurrnn___t_y_p_e shall be one
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of vvooiidd, iinntt, uuiinntt, lloonngg, uulloonngg, lloonngglloonngg, uulloonngglloonngg, ddoouu--
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bbllee, ssttrruucctt, ppttrr or (for ANSI C calling conventions only)
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cchhaarr, sscchhaarr, uucchhaarr, sshhoorrtt, uusshhoorrtt, ffllooaatt, depending on the
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class of _r_e_t_u_r_n___t_y_p_e.
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The _t_y_p_e specifiers in vvaa__ssttaarrtt___t_y_p_e and vvaa__rreettuurrnn___t_y_p_e
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must be the same. The _r_e_t_u_r_n___t_y_p_e specifiers passed to
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vvaa__ssttaarrtt___t_y_p_e and vvaa__rreettuurrnn___t_y_p_e must be the same.
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The _t_y_p_e in vvaa__aarrgg___t_y_p_e shall be one of iinntt, uuiinntt, lloonngg,
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uulloonngg, lloonngglloonngg, uulloonngglloonngg, ddoouubbllee, ssttrruucctt, ppttrr or (for
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ANSI C calling conventions only) cchhaarr, sscchhaarr, uucchhaarr,
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sshhoorrtt, uusshhoorrtt, ffllooaatt, depending on the class of _a_r_g___t_y_p_e.
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In vvaa__ssttaarrtt__ssttrruucctt((_a_l_i_s_t,, _r_e_t_u_r_n___t_y_p_e,, _s_p_l_i_t_t_a_b_l_e));; the
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_s_p_l_i_t_t_a_b_l_e flag specifies whether the struct _r_e_t_u_r_n___t_y_p_e
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can be returned in registers such that every struct field
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fits entirely in a single register. This needs to be spec-
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ified for structs of size 2*sizeof(long). For structs of
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size <= sizeof(long), _s_p_l_i_t_t_a_b_l_e is ignored and assumed to
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be 1. For structs of size > 2*sizeof(long), _s_p_l_i_t_t_a_b_l_e is
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ignored and assumed to be 0. There are some handy macros
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vvaa__wwoorrdd__sspplliittttaabbllee__11 ((_t_y_p_e_1))
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vvaa__wwoorrdd__sspplliittttaabbllee__22 ((_t_y_p_e_1,, _t_y_p_e_2))
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vvaa__wwoorrdd__sspplliittttaabbllee__33 ((_t_y_p_e_1,, _t_y_p_e_2,, _t_y_p_e_3))
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vvaa__wwoorrdd__sspplliittttaabbllee__44 ((_t_y_p_e_1,, _t_y_p_e_2,, _t_y_p_e_3,, _t_y_p_e_4))
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For a struct with three slots
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ssttrruucctt {{ _t_y_p_e_1 _i_d_1;; _t_y_p_e_2 _i_d_2;; _t_y_p_e_3 _i_d_3;; }}
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you can specify _s_p_l_i_t_t_a_b_l_e as vvaa__wwoorrdd__sspplliittttaabbllee__33 ((_t_y_p_e_1,,
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_t_y_p_e_2,, _t_y_p_e_3)) .
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Functions which want to emulate Kernighan & Ritchie style
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functions (i.e., in ANSI C, functions without a typed
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argument list) cannot use the _t_y_p_e values cchhaarr, sscchhaarr,
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uucchhaarr, sshhoorrtt, uusshhoorrtt, ffllooaatt. As prescribed by the default
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K&R C expression promotions, they have to use iinntt instead
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of cchhaarr, sscchhaarr, uucchhaarr, sshhoorrtt, uusshhoorrtt and ddoouubbllee instead of
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The macros vvaa__ssttaarrtt__lloonngglloonngg(()), vvaa__ssttaarrtt__uulloonngglloonngg(()),
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vvaa__rreettuurrnn__lloonngglloonngg(()), vvaa__rreettuurrnn__uulloonngglloonngg(()),
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vvaa__aarrgg__lloonngglloonngg(()) and vvaa__aarrgg__uulloonngglloonngg(()) work only if the
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C compiler has a working lloonngg lloonngg 64-bit integer type.
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The struct types used in vvaa__ssttaarrtt__ssttrruucctt(()) and vvaa__ssttrruucctt(())
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must only contain (signed or unsigned) int, long, long
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long or pointer fields. Struct types containing (signed
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or unsigned) char, short, float, double or other structs
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This example, a possible implementation of eexxeeccll(3) on top
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of eexxeeccvv(2) using vvaarraarrggss(3),
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##iinncclluuddee <<vvaarraarrggss..hh>>
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##ddeeffiinnee MMAAXXAARRGGSS 110000
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//** eexxeeccll iiss ccaalllleedd bbyy eexxeeccll((ffiillee,, aarrgg11,, aarrgg22,, ......,, ((cchhaarr **))00));; **//
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iinntt eexxeeccll ((vvaa__aalliisstt))
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vvaa__lliisstt aapp;;
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cchhaarr** ffiillee;;
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cchhaarr** aarrggss[[MMAAXXAARRGGSS]];;
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iinntt aarrggnnoo == 00;;
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vvaa__ssttaarrtt ((aapp));;
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ffiillee == vvaa__aarrgg((aapp,, cchhaarr**));;
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wwhhiillee ((((aarrggss[[aarrggnnoo]] == vvaa__aarrgg((aapp,, cchhaarr**)))) !!== ((cchhaarr **))00))
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vvaa__eenndd ((aapp));;
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rreettuurrnn eexxeeccvv((ffiillee,, aarrggss));;
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looks like this using vvaaccaallll(3):
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##iinncclluuddee <<vvaaccaallll..hh>>
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##ddeeffiinnee MMAAXXAARRGGSS 110000
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//** eexxeeccll iiss ccaalllleedd bbyy vvaaccaallll((ffiillee,, aarrgg11,, aarrgg22,, ......,, ((cchhaarr **))00));; **//
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vvooiidd eexxeeccll ((aapp))
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vvaa__aalliisstt aapp;;
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cchhaarr** ffiillee;;
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cchhaarr** aarrggss[[MMAAXXAARRGGSS]];;
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iinntt aarrggnnoo == 00;;
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iinntt rreettvvaall;;
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vvaa__ssttaarrtt__iinntt ((aapp));;
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ffiillee == vvaa__aarrgg__ppttrr((aapp,, cchhaarr**));;
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wwhhiillee ((((aarrggss[[aarrggnnoo]] == vvaa__aarrgg__ppttrr((aapp,, cchhaarr**)))) !!== ((cchhaarr **))00))
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rreettvvaall == eexxeeccvv((ffiillee,, aarrggss));;
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vvaa__rreettuurrnn__iinntt ((aapp,, rreettvvaall));;
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vvaaccaallll__ffuunnccttiioonn == &&eexxeeccll;;
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vvaarraarrggss(3), ttrraammppoolliinnee(3), ccaallllbbaacckk(3).
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The current implementations have been tested on a selec-
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tion of common cases but there are probably still many
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There are typically built-in limits on the size of the
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argument-list, which may also include the size of any
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The decision whether a struct is to be returned in regis-
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ters or in memory considers only the struct's size and
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alignment. This is inaccurate: for example, gcc on m68k-
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next returns ssttrruucctt {{ cchhaarr aa,,bb,,cc;; }} in registers and
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ssttrruucctt {{ cchhaarr aa[[33]];; }} in memory, although both types have
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the same size and the same alignment.
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<<vvaaccaallll..hh>> cannot be included when <<vvaarraarrggss..hh>> or
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<<ssttddaarrgg..hh>> is included. (Name clash for vvaa__aalliisstt.)
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The argument list can only be walked once.
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The use of the global variable vvaaccaallll__ffuunnccttiioonn is not
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reentrant. This is fixed in the ccaallllbbaacckk(3) package.
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Knowledge about argument passing conventions can be found
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in the gcc source, file gcc-2.6.3/config/_c_p_u/_c_p_u.h, sec-
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tion "Stack layout; function entry, exit and calling."
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The implementation of varargs for gcc can be found in the
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gcc source, files gcc-2.6.3/ginclude/va*.h.
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gcc's __builtin_saveregs() function is defined in the gcc
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source, file gcc-2.6.3/libgcc2.c.
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Bruno Haible <bruno@clisp.org>
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AACCKKNNOOWWLLEEDDGGEEMMEENNTTSS
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Many ideas and a lot of code were cribbed from the gcc
added
removed
ffcall/vacall/vacall.man
