better glibc i_modulo bug handling

pp-i-modulo code currently detects a glibc bug at runtime, at the 1st
exec of each I_MODULO op.  This is suboptimal; the bug should be
detectable early, and PL_ppaddr[I_MODULO] updated just once, before
any optrees are built.

Then, because we avoid the need to fixup I_MODULO ops in already built
optrees, we can drop the !PERL_DEBUG_READONLY_OPS limitation on the
alternative/workaround I_MODULO implementation that avoids the bug.

perl.c:

bug detection code is copied from PP(i_modulo),
into S_fixup_platform_bugs(), and called from perl_construct().
It patches Perl_pp_i_modulo_1() into PL_ppaddr[I_MODULO] when needed.

pp.c:

PP(i_modulo_0), the original implementation, is renamed to PP(i_modulo)

PP(i_modulo_1), the bug-fix workaround, is renamed _glibc_bugfix
                it is #ifdefd as before, but dropping !PERL_DEBUG_READONLY_OPS

PP(i_modulo) - the 1st-exec switcher code, is dropped

ocode.pl:

Two i_modulo entries are added to @raw_alias.
- 1st alias:  Perl_pp_i_modulo		    => 'i_modulo'
- 2nd alt:    Perl_pp_i_modulo_glibc_bugfix => 'i_modulo'

1st is a restatement of the default alias/mapping that would be
created without the line.  2nd line is then seen as alternative to the
explicit mapping set by 1st.

Alternative functions are written to pp_proto.h after the standard
Perl_pp_* list, and include #if-cond, #endif wrappings, as was
specified by 2nd @raw_alias addition.

Changes tested by inserting '1 ||' into the 3 ifdefs and bug-detection code.

TODO:

In pp_proto.h generation, the #ifdef wrapping code which handles the
alternative functions looks like it should also be used for the
non-alternate functions.  In particular, there are a handful of
pp-function prototypes that should be wrapped with #ifdef HAS_SOCKET.
That said, there have been no problem reports, so I left it alone.

TonyC: make S_fixup_platform_bugs static, porting/libperl.t was failing.

1 files changed, 2 insertions, 52 deletions

diff --git a/pp.c b/pp.c
index 4a2cde05e0..0fff0d9f66 100644
--- a/pp.c
+++ b/pp.c
@@ -2785,13 +2785,7 @@ PP(pp_i_divide)
     }
 }
 
-#if defined(__GLIBC__) && IVSIZE == 8 && !defined(PERL_DEBUG_READONLY_OPS) \
-    && ( __GLIBC__ < 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ < 8))
-STATIC
-PP(pp_i_modulo_0)
-#else
 PP(pp_i_modulo)
-#endif
 {
      /* This is the vanilla old i_modulo. */
      dSP; dATARGET;
@@ -2809,11 +2803,10 @@ PP(pp_i_modulo)
      }
 }
 
-#if defined(__GLIBC__) && IVSIZE == 8 && !defined(PERL_DEBUG_READONLY_OPS) \
+#if defined(__GLIBC__) && IVSIZE == 8 \
     && ( __GLIBC__ < 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ < 8))
-STATIC
-PP(pp_i_modulo_1)
 
+PP(pp_i_modulo_glibc_bugfix)
 {
      /* This is the i_modulo with the workaround for the _moddi3 bug
       * in (at least) glibc 2.2.5 (the PERL_ABS() the workaround).
@@ -2832,49 +2825,6 @@ PP(pp_i_modulo_1)
 	  RETURN;
      }
 }
-
-PP(pp_i_modulo)
-{
-     dVAR; dSP; dATARGET;
-     tryAMAGICbin_MG(modulo_amg, AMGf_assign);
-     {
-	  dPOPTOPiirl_nomg;
-	  if (!right)
-	       DIE(aTHX_ "Illegal modulus zero");
-	  /* The assumption is to use hereafter the old vanilla version... */
-	  PL_op->op_ppaddr =
-	       PL_ppaddr[OP_I_MODULO] =
-	           Perl_pp_i_modulo_0;
-	  /* .. but if we have glibc, we might have a buggy _moddi3
-	   * (at least glibc 2.2.5 is known to have this bug), in other
-	   * words our integer modulus with negative quad as the second
-	   * argument might be broken.  Test for this and re-patch the
-	   * opcode dispatch table if that is the case, remembering to
-	   * also apply the workaround so that this first round works
-	   * right, too.  See [perl #9402] for more information. */
-	  {
-	       IV l =   3;
-	       IV r = -10;
-	       /* Cannot do this check with inlined IV constants since
-		* that seems to work correctly even with the buggy glibc. */
-	       if (l % r == -3) {
-		    /* Yikes, we have the bug.
-		     * Patch in the workaround version. */
-		    PL_op->op_ppaddr =
-			 PL_ppaddr[OP_I_MODULO] =
-			     &Perl_pp_i_modulo_1;
-		    /* Make certain we work right this time, too. */
-		    right = PERL_ABS(right);
-	       }
-	  }
-	  /* avoid FPE_INTOVF on some platforms when left is IV_MIN */
-	  if (right == -1)
-	      SETi( 0 );
-	  else
-	      SETi( left % right );
-	  RETURN;
-     }
-}
 #endif
 
 PP(pp_i_add)