Newx compiler warnings

wbirkett has asked for the wisdom of the Perl Monks concerning the following question:

The following code is used in an XS to make an array full of 0's. It works fine.

/* create a Perl array filled with zeros */
SV* vec_zeros(int m) {
    int i;
    AV *myav;
    SV **svs;
    
    /* allocate memory for array */
    *svs = (SV **) malloc(m * sizeof(SV *));

    /* for m array elements */
    for (i = 0; i < m; i++) {

        /* create a Perl SV (scalar value) */
        svs[i] = sv_newmortal();

        /* set SV to 0 */
        sv_setnv((SV*)svs[i], 0.0f);

    }

    /* make Perl AV */
    myav = av_make(m, svs);

    /* free allocated memory */
    free(svs);

    /* return array reference */
    return newRV_noinc((SV*) myav);
    
}
[download]

Heeding advice in 'perlguts', I changed 'malloc' to 'Newx' and 'free' to 'Safefree'

/* create a Perl array filled with zeros */
SV* vec_zeros(int m) {
    int i;
    AV *myav;
    SV **svs;
    
    /* allocate memory for array */
    Newx(svs, m, SV *);

    /* for m array elements */
    for (i = 0; i < m; i++) {

        /* create a Perl SV (scalar value) */
        svs[i] = sv_newmortal();

        /* set SV to 0 */
        sv_setnv((SV*)svs[i], 0.0f);

    }

    /* make Perl AV */
    myav = av_make(m, svs);

    /* free allocated memory */
    Safefree(svs);

    /* return array reference */
    return newRV_noinc((SV*) myav);
    
}
[download]

Now I get the following warnings when I compile:

xs_arrays.c: In function ‘vec_zeros’:
xs_arrays.c:247: warning: format not a string literal and no format ar
+guments
xs_arrays.c: In function ‘vec_zeros’:
xs_arrays.c:247: warning: format not a string literal and no format ar
+guments
xs_arrays.c: In function ‘vec_zeros’:
xs_arrays.c:247: warning: format not a string literal and no format ar
+guments
[download]

Any idea what this means, and how to correct it? I'm using Perl 5.10.0, as supplied on Mac OS X:

Summary of my perl5 (revision 5 version 10 subversion 0) configuration
+:
  Platform:
    osname=darwin, osvers=10.0, archname=darwin-thread-multi-2level
    uname='darwin neige.apple.com 10.0 darwin kernel version 10.0.0d8:
+ tue may 5 19:29:59 pdt 2009; root:xnu-1437.2~2release_i386 i386 '
    config_args='-ds -e -Dprefix=/usr -Dccflags=-g  -pipe  -Dldflags= 
+-Dman3ext=3pm -Duseithreads -Duseshrplib -Dinc_version_list=none -Dcc
+=gcc-4.2'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=und
+ef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='gcc-4.2', ccflags ='-arch x86_64 -arch i386 -arch ppc -g -pipe
+ -fno-common -DPERL_DARWIN -fno-strict-aliasing -I/usr/local/include'
+,
    optimize='-Os',
    cppflags='-g -pipe -fno-common -DPERL_DARWIN -fno-strict-aliasing 
+-I/usr/local/include'
    ccversion='', gccversion='4.2.1 (Apple Inc. build 5646)', gccosand
+vers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1
+6
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t',
+ lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='gcc-4.2 -mmacosx-version-min=10.6', ldflags ='-arch x86_64 -ar
+ch i386 -arch ppc -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib
    libs=-ldbm -ldl -lm -lutil -lc
    perllibs=-ldl -lm -lutil -lc
    libc=/usr/lib/libc.dylib, so=dylib, useshrplib=true, libperl=libpe
+rl.dylib
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=bundle, d_dlsymun=undef, ccdlflags=' '
    cccdlflags=' ', lddlflags='-arch x86_64 -arch i386 -arch ppc -bund
+le -undefined dynamic_lookup -L/usr/local/lib'


Characteristics of this binary (from libperl): 
  Compile-time options: MULTIPLICITY PERL_DONT_CREATE_GVSV
                        PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP USE_64_
+BIT_ALL
                        USE_64_BIT_INT USE_ITHREADS USE_LARGE_FILES
                        USE_PERLIO USE_REENTRANT_API
  Locally applied patches:
    /Library/Perl/Updates/<version> comes before system perl directori
+es
    installprivlib and installarchlib points to the Updates directory
  Built under darwin
  Compiled at Jun 24 2009 00:35:27
  @INC:
    /Library/Perl/Updates/5.10.0/darwin-thread-multi-2level
    /Library/Perl/Updates/5.10.0
    /System/Library/Perl/5.10.0/darwin-thread-multi-2level
    /System/Library/Perl/5.10.0
    /Library/Perl/5.10.0/darwin-thread-multi-2level
    /Library/Perl/5.10.0
    /Network/Library/Perl/5.10.0/darwin-thread-multi-2level
    /Network/Library/Perl/5.10.0
    /Network/Library/Perl
    /System/Library/Perl/Extras/5.10.0/darwin-thread-multi-2level
    /System/Library/Perl/Extras/5.10.0
[download]

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Replies are listed 'Best First'.
Re: Newx compiler warnings by Eliya (Vicar) on Mar 19, 2011 at 15:02 UTC
`xs_arrays.c:247: warning: format not a string literal and no format arguments` Normally, gcc issues this warning if `printf` functions are being called with a non-literal first argument, and the respective warnings are enabled. (See also `-Wformat, -Wformat-nonliteral, -Wformat-security` in the gcc man page) For example `#include <stdio.h> int main() { char foo[100]; scanf("%s", foo); printf(foo); / compiler cannot inspect contents of foo / return 0; }` [download] `$ gcc -Wformat -Wformat-security nonlit.c nonlit.c: In function 'main': nonlit.c:5: warning: format not a string literal and no format argumen +ts` [download] It seems those warnings were enabled by default in gcc 4.2.1 (with my newer version I explicitly have to request them). That said, I'm not sure where there would be something `printf`-related in your code... What is line 247? Even the preprocessor expansion¹ of your snippet reveals no `(s\|f)printf` whatsoever: SV vec_zeros(int m) { int i; AV myav; SV svs; (svs = ((void)(sizeof(SV ) > 1 && (m) > ((size_t)~0)/sizeof(SV ) + && (Perl_croak_nocontext(PL_memory_wrap),0)), (SV )Perl_safesysmal +loc((size_t)((m)sizeof(SV ))))); for (i = 0; i < m; i++) { svs[i] = Perl_sv_newmortal(((PerlInterpreter )pthread_getspec +ific((Perl_Gthr_key_ptr(((void )0)))))); Perl_sv_setnv(((PerlInterpreter )pthread_getspecific((Perl_G +thr_key_ptr(((void )0))))), (SV)svs[i],0.0f); } myav = Perl_av_make(((PerlInterpreter )pthread_getspecific((Perl +_Gthr_key_ptr(((void )0))))), m,svs); Perl_safesysfree((void )(svs)); return Perl_newRV_noinc(((PerlInterpreter )pthread_getspecific(( +Perl_Gthr_key_ptr(((void )0))))), (SV) myav); } [download] Anyhow, most likely, you can just ignore the warning, or disable it with `-Wno-format`. ___ ¹ done with gcc option `-E`, on a Linux system, with a perl built with `"usemymalloc=n"` (like yours).	[reply] [d/l] [select]
Re^2: Newx compiler warnings by dave_the_m (Monsignor) on Mar 19, 2011 at 18:57 UTC
Perl_croak_nocontext() is marked as being 'printf'-like, so it will generate similar warnings. The definition of the Newx macro (or rather the underlying MEM_WRAP_CHECK_1 macro) was fixed in 5.12.0 to avoid this (harmless) warning. Dave.	[reply]