NAME

Measure sizeof() of Perl's C Structures

Description

This document describes the sizeof various structures, as determined by util/sizeof.pl. These measurements are mainly for research purposes into making Perl things smaller, or rather, how to use less Perl things.

Perl Structures

Structures diagrams are courtesy gdb (print pretty) and a bit of hand crafting.

CV - 229 minimum, 254 minimum w/ symbol table entry

cv = {
   sv_any = {        // XPVCV *
       xpv_pv = 0x0, // char *
       xpv_cur = 0,  // STRLEN
       xpv_len = 0,  // STRLEN
       xof_off = 0 , // IV
       xnv_nv = 0,   // NV
       xmg_magic = 0x0, // MAGIC *
       xmg_stash = 0x0, // HV *
       xcv_stash = 0x0, // HV *
       xcv_start = 0x0, // OP *
       xcv_root = 0x0,  // OP *
       xcv_xsub = 0x0,  // void (*)(register PerlInterpreter *, CV *)
       xcv_xsubany = {  // ANY
           any_ptr = 0x0,
           any_i32 = 0,
           any_iv = 0,
           any_long = 0,
           any_dptr = 0,
           any_dxptr = 0
       },
       xcv_gv = { // GV *
           sv_any = { // void *
               xpv_pv = 0x0, // char *
               xpv_cur = 0,  // STRLEN
               xpv_len = 0,  // STRLEN
               xiv_iv = 0,   // IV
               xnv_nv = 0,   // NV
               xmg_magic =  { // MAGIC *
                   mg_moremagic = 0x0, // MAGIC *
                   mg_virtual = 0x0,   // MGVTBL *
                   mg_private = 0,     // U16
                   mg_type = 0,        // char
                   mg_flags = 0,       // U8
                   mg_obj = 0x0,       // SV *
                   mg_ptr = 0x0,       // char *
                   mg_len = 0,         // I32
               },
               xmg_stash = 0x0, // HV *
               xgv_gp = { // GP *
                   gp_sv = { // SV *
                       sv_any = 0x0,  // void *
                       sv_refcnt = 0, // U32
                       sv_flags = 0   // U32
                   },
                   gp_refcnt = 0, // U32
                   gp_io = 0x0,   // struct io *
                   gp_form = 0x0, // CV *
                   gp_av = 0x0,   // AV *
                   gp_hv = 0x0,   // HV *
                   gp_egv = 0x0,  // GV *
                   gp_cv = 0x0,   // CV *
                   gp_cvgen = 0,  // U32
                   gp_flags = 0,  // U32
                   gp_line = 0,   // line_t
                   gp_file = 0x0, // char *
               },
               xgv_name = 0x0,  // char *
               xgv_namelen = 0, // STRLEN
               xgv_stash = 0x0, // void *
               xgv_flags = 0,   // U8
           },
           sv_refcnt = 0, // U32
           sv_flags = 0,  // U32
       },
       xcv_file = 0x0, // char *
       xcv_depth = 0, // long
       xcv_padlist = 0x0, // AV *
       xcv_outside = 0x0, // CV *
       xcv_flags = 0, // cv_flags_t
   }
   sv_refcnt = 0, // U32
   sv_flags = 0,  // U32
};

In addition to the minimum bytes:

name of the subroutine: GvNAMELEN(CvGV(cv))+1

symbol table entry: HvENTRY (25 + GvNAMELEN(CvGV(cv))+1)

minimum sizeof(AV) * 3: xcv_padlist if !CvXSUB(cv)

CvROOT(cv) optree

HV - 60 minmum

hv = {
   sv_any = { // SV *
       xhv_array = 0x0,  // char *
       xhv_fill = 0,     // STRLEN
       xhv_max = 0,      // STRLEN
       xhv_keys = 0,     // IV
       xnv_nv = 0,       // NV
       xmg_magic = 0x0,  // MAGIC *
       xmg_stash = 0x0,  // HV *
       xhv_riter = 0,    // I32
       xhv_eiter = 0x0,  // HE *
       xhv_pmroot = 0x0, // PMOP *
       xhv_name = 0x0    // char *
   },
   sv_refcnt = 0, // U32
   sv_flags = 0,  // U32
};

Each entry adds sizeof(HvENTRY), minimum of 7 (initial xhv_max). Note that keys of the same value share sizeof(HEK), across all hashes.

HvENTRY - 25 + HeKLEN+1

sizeof(HE *) + sizeof(HE) + sizeof(HEK)

HE - 12

he = {
   hent_next = 0x0, // HE *
   hent_hek = 0x0,  // HEK *
   hent_val = 0x0   // SV *
};

HEK - 9 + hek_len

hek = {
   hek_hash = 0, // U32
   hek_len = 0,  // I32
   hek_key = 0,  // char
};

AV - 53

av = {
   sv_any =  { // SV *
       xav_array = 0x0,  // char *
       xav_fill = 0,     // size_t
       xav_max = 0,      // size_t
       xof_off = 0,      // IV
       xnv_nv = 0,       // NV
       xmg_magic = 0x0,  // MAGIC *
       xmg_stash = 0x0,  // HV *
       xav_alloc = 0x0,  // SV **
       xav_arylen = 0x0, // SV *
       xav_flags = 0,    // U8
   },
   sv_refcnt = 0, // U32
   sv_flags = 0   // U32
};

In addition to the minimum bytes:

AvFILL(av) * sizeof(SV *)

SEE ALSO

perlguts(3), B::Size(3),

http://gisle.aas.no/perl/illguts/

Maintainers

Maintainer is the person(s) you should contact with updates, corrections and patches.

• Doug MacEachern <dougm (at) covalent.net>

Authors

• Doug MacEachern <dougm (at) covalent.net>