eval_pv fails to compile on non-gcc compilers with Perl < 5.031

[tglsfdc]

I've found that the eval_pv implementation added in PPPort 3.54 does not work on compilers that don't support gcc-like statements within expressions. Without BRACE_GROUPS, that macro looks like

#define eval_pv(p, croak_on_error) ((PL_Sv = Perl_eval_pv(aTHX_ p, 0)), (croak_on_error && (SvROK(ERRSV) || SvTRUE(ERRSV)) && (croak_sv(ERRSV), 1)), PL_Sv)

but croak_sv expands to something involving STMT_START { ... } STMT_END, so kaboom.

Observed with perl 5.12.5 and Solaris 11.3's acomp, and also with perl 5.8.9 and a really hoary HPUX compiler. Things were fine before we updated to a late-model ppport.h ...

[pali]

Would following patch fix your issue?

diff --git a/parts/inc/call b/parts/inc/call
index 351f8cc5547d..756378c7f453 100644
--- a/parts/inc/call
+++ b/parts/inc/call
@@ -51,7 +51,8 @@ __UNDEFINED__ PERL_LOADMOD_IMPORT_OPS   0x4
 #if defined(PERL_USE_GCC_BRACE_GROUPS)
 # define D_PPP_CROAK_IF_ERROR(cond) ({ SV *_errsv; ((cond) && (_errsv = ERRSV) && (SvROK(_errsv) || SvTRUE(_errsv)) && (croak_sv(_errsv), 1)); })
 #else
-# define D_PPP_CROAK_IF_ERROR(cond) ((cond) && (SvROK(ERRSV) || SvTRUE(ERRSV)) && (croak_sv(ERRSV), 1))
+  static void D_PPP_CROAK_IF_ERROR(int cond) { dTHX; SV *errsv; if (!cond) return; errsv = ERRSV; if (SvROK(errsv) || SvTRUE(errsv)) croak_sv(errsv); }
+# define D_PPP_CROAK_IF_ERROR(cond) D_PPP_CROAK_IF_ERROR(cond)
 #endif
 
 #ifndef G_METHOD

[tglsfdc]

As given, that doesn't seem to work for me: I get a bunch of errors/warnings that look like the proposed inline function isn't quite right.

cc: "ppport.h", line 15051: error 1000: Unexpected symbol: "void".
cc: "ppport.h", line 15051: error 1588: "my_perl" undefined.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1527: Incompatible types in cast: Must cast from scalar to scalar or to void type.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1554: Indirection must be through a pointer.
cc: "ppport.h", line 15051: error 1552: First expression of ?: must be arithmetic.
cc: "ppport.h", line 15051: warning 563: Argument #1 is not the correct type.
cc: "ppport.h", line 15051: warning 604: Pointers are not assignment-compatible.
cc: "ppport.h", line 15051: warning 563: Argument #2 is not the correct type.
cc: "ppport.h", line 15051: warning 563: Argument #1 is not the correct type.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1532: Reference through a non-pointer.
cc: "ppport.h", line 15051: error 1527: Incompatible types in cast: Must cast from scalar to scalar or to void type.
cc: "ppport.h", line 15051: warning 604: Pointers are not assignment-compatible.
cc: "ppport.h", line 15051: warning 563: Argument #2 is not the correct type.
cc: "ppport.h", line 15051: warning 527: Integral value implicitly converted to pointer in assignment.
cc: "ppport.h", line 15051: warning 563: Argument #4 is not the correct type.
make: *** [plperl.o] Error 1

You might be able to make something of the idea with some adjustments, but I don't know this code well enough to suggest exactly what.

[pali]

I updated patch, could you try it if it helps?

[tglsfdc]

After a bit more poking at it, the primary reason for the compile failures is that you missed doing the pTHX_/aTHX_ dance. For me, editing ppport.h like this:

-# define D_PPP_CROAK_IF_ERROR(cond) ((cond) && (SvROK(ERRSV) || SvTRUE(ERRSV)) && (croak_sv(ERRSV), 1))
+void D_PPP_CROAK_IF_ERROR(pTHX_ int cond) { SV *errsv; if (!cond) return; errsv = ERRSV; if (SvROK(errsv) || SvTRUE(errsv)) croak_sv(errsv); }
+# define D_PPP_CROAK_IF_ERROR(cond) D_PPP_CROAK_IF_ERROR(aTHX_ cond)

allows the compile to go through, but then (unsurprisingly) I get link-time errors about multiple modules defining D_PPP_CROAK_IF_ERROR. Not sure why the STATIC_INLINE bit doesn't work, but it doesn't compile with that.

[pali]

After a bit more poking at it, the primary reason for the compile failures is that you missed doing the pTHX_/aTHX_ dance.

That is why I updated patch with dTHX; line. Could you try if dTHX; is enough instead of using pTHX_ and aTHX_?

allows the compile to go through, but then (unsurprisingly) I get link-time errors about multiple modules defining D_PPP_CROAK_IF_ERROR. Not sure why the STATIC_INLINE bit doesn't work, but it doesn't compile with that.

That makes sense. D_PPP_CROAK_IF_ERROR has to be static. inline is just optimization. Could you try to replace STATIC_INLINE with just static keyword?

[tglsfdc]

Oh! My fault, I did not notice that you'd made that edit in addition to removal of the STATIC_INLINE bit. Yes, "dTHX;" works equally well as pTHX_/aTHX_, at least in my test case.

With the particular ancient compiler I'm testing, declaring the function as plain "static" works fine, with no unused-function warnings. I'm worried though that other compilers will whine about it in modules that use neither eval_pv nor eval_sv.

[tglsfdc]

Oh ... the reason PERL_STATIC_INLINE fails is that I'm testing against perl 5.8.9, which if I'm reading the chart right lacks that symbol (and I don't see it in grepping the perl headers, either). So plain "static" might be the only way.

[pali]

Could you check if macro PERL_STATIC_INLINE is defined? In some of my modules I have at the beginning:

#ifndef PERL_STATIC_INLINE
#define PERL_STATIC_INLINE static
#endif

So I have feeling that Devel::PPPort does not define PERL_STATIC_INLINE for old perl versions with old compilers.

[tglsfdc]

Indeed, there is no such definition in ppport.h.

[pali]

Ok! So seems that Devel::PPPort needs to backport PERL_STATIC_INLINE definition and then it should work.

[tglsfdc]

I'm still a bit worried about the unused-function-warning aspect, but maybe the set of cases where you'd get one is small enough to not bother about. Most people should be developing against versions that have PERL_STATIC_INLINE, and having that properly defined should be enough to prevent a warning.

[pali]

Could you try following patch for backporting PERL_STATIC_INLINE macro?

diff --git a/parts/inc/misc b/parts/inc/misc
index 6d3edbc5af6d..a74e8cf8a017 100644
--- a/parts/inc/misc
+++ b/parts/inc/misc
@@ -19,6 +19,7 @@ MUTABLE_PTR
 NVTYPE
 PERLIO_FUNCS_CAST
 PERLIO_FUNCS_DECL
+PERL_STATIC_INLINE
 PERL_UNUSED_ARG
 PERL_UNUSED_CONTEXT
 PERL_UNUSED_DECL
@@ -38,6 +39,12 @@ ASSUME
 
 =implementation
 
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
+__UNDEFINED__ PERL_STATIC_INLINE static inline
+#else
+__UNDEFINED__ PERL_STATIC_INLINE static
+#endif
+
 __UNDEFINED__ cBOOL(cbool) ((cbool) ? (bool)1 : (bool)0)
 __UNDEFINED__ OpHAS_SIBLING(o)      (cBOOL((o)->op_sibling))
 __UNDEFINED__ OpSIBLING(o)          (0 + (o)->op_sibling)

Ad unused-function-warning, we are dealing with old compilers, I would not spend too much time how to mute false-positive warnings for these compilers. Just to ensure that code is correct and accepted by older compilers. If you need to check that code is correct, just use some new compiler...

[tglsfdc]

Sorry, I'm not really set up to build Devel::PPPort from source. But I can confirm that editing ppport.h like this passes my tests:
ppport.patch.txt

[pali]

Pull request with fix is here: #217
Hopefully it is enough for fixing this issue.