[perl #131645] Fix assert fail in pp_sselect

pp_sselect (4-arg select) process its first three bitfield arguments
first, making sure each one has a valid PV, and then it moves on to
the final, timeout argument.

SvGETMAGIC() on the timeout argument will wipe out any values the SV
holds, so if the same scalar is used as a bitfield argument *and* as
the timeout, it will no longer hold a valid PV.

Assertions later in pp_sselect make sure there is a valid PV.

This commit solves the assertion failure by making a temporary copy of
any gmagical or overloaded argument.  When the temporary copy is made,
the values written to the temporary copies of the bitfield arguments
are then copied back to the original magical arguments.

pp_sys.c

@@ -1149,6 +1149,7 @@ PP(pp_sselect)
     struct timeval *tbuf = &timebuf;
     I32 growsize;
     char *fd_sets[4];
+    SV *svs[4];
 #if BYTEORDER != 0x1234 && BYTEORDER != 0x12345678
 	I32 masksize;
 	I32 offset;
@@ -1164,7 +1165,7 @@ PP(pp_sselect)
 
     SP -= 4;
     for (i = 1; i <= 3; i++) {
-	SV * const sv = SP[i];
+	SV * const sv = svs[i] = SP[i];
 	SvGETMAGIC(sv);
 	if (!SvOK(sv))
 	    continue;
@@ -1177,9 +1178,14 @@ PP(pp_sselect)
 	    if (!SvPOKp(sv))
 		Perl_ck_warner(aTHX_ packWARN(WARN_MISC),
 				    "Non-string passed as bitmask");
-	    SvPV_force_nomg_nolen(sv);	/* force string conversion */
+	    if (SvGAMAGIC(sv)) {
+		svs[i] = sv_newmortal();
+		sv_copypv_nomg(svs[i], sv);
+	    }
+	    else
+		SvPV_force_nomg_nolen(sv); /* force string conversion */
 	}
-	j = SvCUR(sv);
+	j = SvCUR(svs[i]);
 	if (maxlen < j)
 	    maxlen = j;
     }
@@ -1228,7 +1234,7 @@ PP(pp_sselect)
 	tbuf = NULL;
 
     for (i = 1; i <= 3; i++) {
-	sv = SP[i];
+	sv = svs[i];
 	if (!SvOK(sv) || SvCUR(sv) == 0) {
 	    fd_sets[i] = 0;
 	    continue;
@@ -1275,7 +1281,7 @@ PP(pp_sselect)
 #endif
     for (i = 1; i <= 3; i++) {
 	if (fd_sets[i]) {
-	    sv = SP[i];
+	    sv = svs[i];
 #if BYTEORDER != 0x1234 && BYTEORDER != 0x12345678
 	    s = SvPVX(sv);
 	    for (offset = 0; offset < growsize; offset += masksize) {
@@ -1284,7 +1290,10 @@ PP(pp_sselect)
 	    }
 	    Safefree(fd_sets[i]);
 #endif
-	    SvSETMAGIC(sv);
+	    if (sv != SP[i])
+		SvSetMagicSV(SP[i], sv);
+	    else
+		SvSETMAGIC(sv);
 	}
     }
 

t/op/sselect.t

@@ -13,7 +13,7 @@ BEGIN {
 skip_all("Win32 miniperl has no socket select")
   if $^O eq "MSWin32" && is_miniperl();
 
-plan (15);
+plan (16);
 
 my $blank = "";
 eval {select undef, $blank, $blank, 0};
@@ -95,3 +95,12 @@ note("diff=$diff under=$under");
     select (undef, undef, undef, $sleep);
     ::is($count, 1, 'RT120102');
 }
+
+package _131645{
+    sub TIESCALAR { bless [] }
+    sub FETCH     { 0        }
+    sub STORE     {          }
+}
+tie $tie, _131645::;
+select ($tie, undef, undef, $tie);
+ok("no crash from select $numeric_tie, undef, undef, $numeric_tie")