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Postings from July 2010
On Tue, Jul 13, 2010 at 03:13:00AM -0400, George Greer wrote:
> sv.c: In function ‘I32 Perl_sv_cmp(SV*, SV*)’:
> sv.c:6849: error: invalid conversion from ‘const void*’ to ‘const char*’
> sv.c:6849: error: initializing argument 1 of ‘I32 Perl_my_memcmp(const char*, const char*, I32)’
> sv.c:6849: error: initializing argument 2 of ‘I32 Perl_my_memcmp(const char*, const char*, I32)’
> sv.c: In function ‘I32 Perl_sv_cmp_locale(SV*, SV*)’:
> sv.c:6906: error: invalid conversion from ‘void*’ to ‘const char*’
> sv.c:6906: error: initializing argument 1 of ‘I32 Perl_my_memcmp(const char*, const char*, I32)’
> sv.c:6906: error: initializing argument 2 of ‘I32 Perl_my_memcmp(const char*, const char*, I32)’
This appears to be two problems:
a) the prototype for the replacement Perl_my_memcmp() doesn't match
the standard C memcmp(). Presumably this matches historical
(pre-ANSI) memcmp.
b) Configure doesn't find the available memcmp() - so why?
One thing that confused me initially was why it worked under gcc but
not under g++. hints/linux.sh defaults use of nm when building with
g++, while for gcc, nm isn't used because the library is detected as
GNU libc.
The nm mechanism is failing because of a GNU extension:
tony@saturn-ubuntu64:~$ nm --dynamic /lib64/libc.so.6 | grep memcmp
0000000000085260 i memcmp
000000000008e780 T wmemcmp
From man nm:
"i" For PE format files this indicates that the symbol is in a
section specific to the implementation of DLLs. For ELF format
files this indicates that the symbol is an indirect function.
This is a GNU extension to the standard set of ELF symbol
types. It indicates a symbol which if referenced by a
relocation does not evaluate to its address, but instead must
be invoked at runtime. The runtime execution will then return
the value to be used in the relocation.
Which presumably a symbol with a type of "i" should be treated as
defined.
As simple change:
diff --git a/Configure b/Configure
index 4217f8c..db52ff8 100755
--- a/Configure
+++ b/Configure
@@ -7672,7 +7672,7 @@ $echo $n ".$c"
$grep fprintf libc.tmp > libc.ptf
xscan='eval "<libc.ptf $com >libc.list"; $echo $n ".$c" >&4'
xrun='eval "<libc.tmp $com >libc.list"; echo "done." >&4'
-xxx='[ADTSIW]'
+xxx='[ADTSIWi]'
if com="$sed -n -e 's/__IO//' -e 's/^.* $xxx *//p'";\
eval $xscan;\
$contains '^fprintf$' libc.list >/dev/null 2>&1; then
allows perl to build and test successfully.
(Configure change, so not committed.)
An alternative would be to remove the usenm hint for g++, but
presumably that was added for a reason.
Should Perl_my_memcmp() be changed to match ANSI C?
Tony
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