Re: [Swig-devel] valgrind reports "invalid read" in DohvPrintf (fio.c)

[Kris T. <kri...@gm...>]

>From: William Fulton, Sent: 10 June 2014 19:25
> On 08/06/14 12:18, Kris Thielemans wrote:
> > Hi
> >
> > When attempting to debug my matlab enhancements, I ran valgrind on my
> swig
> > fork https://github.com/KrisThielemans/swig (forked from Joel
Andersson's
> > fork which happened at 3rd of April 2014).
> >
> > Valgrind gives me a lot of "invalid reads", always in the same place,
> > independent of which target language that I use. Example:
> >
> >
> > ==25156==
> > ==25156== Invalid read of size 4
> > ==25156==    at 0x41E76B: DohvPrintf (fio.c:323)
> > ==25156==    by 0x41EB56: DohPrintf (fio.c:435)
> > ==25156==    by 0x4F423A: expand_macro (cpp.c:958)
> > ==25156==    by 0x4F5114: Preprocessor_replace (cpp.c:1149)
> > ==25156==    by 0x4F5417: add_chunk (cpp.c:1278)
> > ==25156==    by 0x4F2D14: Preprocessor_parse (cpp.c:1356)
> > ==25156==    by 0x4F32B1: Preprocessor_parse (cpp.c:1880)
> > ==25156==    by 0x4F32B1: Preprocessor_parse (cpp.c:1880)
> > ==25156==    by 0x4F32B1: Preprocessor_parse (cpp.c:1880)
> > ==25156==    by 0x4F32B1: Preprocessor_parse (cpp.c:1880)
> > ==25156==    by 0x48AC3E: SWIG_main(int, char**, Language*)
> (main.cxx:1065)
> > ==25156==    by 0x406084: main (swigmain.cxx:208)
> > ==25156==  Address 0x6275a0c is 908 bytes inside a block of size 911
alloc'd
> > ==25156==    at 0x4C2AB80: malloc (in
> > /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
> > ==25156==    by 0x41EA6D: DohvPrintf (fio.c:316)
> > ==25156==    by 0x41EB56: DohPrintf (fio.c:435)
> > ==25156==    by 0x4F423A: expand_macro (cpp.c:958)
> > ==25156==    by 0x4F5114: Preprocessor_replace (cpp.c:1149)
> > ==25156==    by 0x4F5417: add_chunk (cpp.c:1278)
> > ==25156==    by 0x4F2D14: Preprocessor_parse (cpp.c:1356)
> > ==25156==    by 0x4F32B1: Preprocessor_parse (cpp.c:1880)
> > ==25156==    by 0x4F32B1: Preprocessor_parse (cpp.c:1880)
> > ==25156==    by 0x4F32B1: Preprocessor_parse (cpp.c:1880)
> > ==25156==    by 0x4F32B1: Preprocessor_parse (cpp.c:1880)
> > ==25156==    by 0x48AC3E: SWIG_main(int, char**, Language*)
> (main.cxx:1065)
> > ==25156==
> >
> >
> > The relevant lines in fio.c are
> >
> > L316    stemp = (char *) DohMalloc(maxwidth + 1);
> >
> > L323    if (Writen(so, stemp, strlen(stemp)) < 0)
> >
> > All these warnings disappear if I change L316 to
> >
> >             stemp = (char *) DohMalloc(maxwidth + 4);
> >
> > why that would be, I have no idea. (maybe something to do with
pointer-type
> > conversions and memory being read be in 32bit words as opposed to 8bit
> > bytes?)
> >
> Well, if you get to the bottom of it, let us know!
> 
> Because the memory is recycled from pools in Swig, Valgrind isn't always
> that useful for debugging. What you are seeing might be a side effect of
> a real problem which will be more easily tracked down by defining
> SWIG_DEBUG_DELETE in base.c and DOH_DEBUG_MEMORY_POOLS in base.c.
> 

Hi William
Enabling these 2 doesn't show up any errors in "normal" swig (of course, it
found a bug in the MATLAB module, see separate email). Also, I discovered
that the valgrind errors disappear when I change the optimisation level of
the C compiler down from -O2 to -O1 (or no optimisation). Hmmm, a compiler
bug? I'm using gcc (Ubuntu 4.8.2-19ubuntu1).

As I can't see anything wrong in the code in the first place (admittedly I
didn't look very hard), I'll ignore this therefore.

Kris