Re: Crash when using libcurl as part of a project - Visual Studio 2005
Date: Tue, 6 Nov 2007 00:22:34 -0800 (PST)
--- Cristi <eblis102_at_yahoo.com> wrote:
> > > I'm using the source code for libcurl itself in the project, i am
> > not using
> > > libcurl as a dyanamic library.
> > I would recommend that you instead build a lib (static or DLL) and
> > use that,
> > since it'll make it easier for you to upgrade to newer libcurls in
> > the future.
> I have libcurl in it's own folder, i can just copy-paste the new
> code in there and everything should compile.
> > > But if i use the same dll but compiled in Release mode i get a
> > crash in
> > > curl_easy_perform(). I've traced through the call stack a bit and
> > i've
> > > noticed that the line it fails in is from hash.c, line no 99: h =
> > (struct
> > > curl_hash *) malloc(sizeof(struct curl_hash));
> > >
> > > The callstack also shows malloc.c above hash.c and the error is
> > invalid
> > > access to memory location, 0x00000000.
> > I would say that this is due to you mixing memory "models" between
> > various
> > components in your application, or that something outside of
> > is
> > destroying memory somewhere at some point.
> The weird thing is that if I compile the plugin in Debug mode (either
> dynamically or statically linking it to the MSVC runtime) it works
> > Other than so, I would recommend using some kind of memory
> > tracking/supervising tool (purify, valgrind or similar) to figure
> > this out.
> > > it seems as though there's something wrong with the memory
> > functions
> > > that curl knows about.
> > >
> > > If I compile the curlib project with the most verbose warning
> > setting
> > > turned on I get the following warning:
> > > .\easy.c(205) : warning C4232: nonstandard extension used :
> > > 'Curl_cmalloc' : address of dllimport 'malloc' is not static,
> > identity
> > > not guaranteed
> > > d:\usr\Microsoft Visual Studio 8\VC\include\stdlib.h(594)
> > see
> > > declaration of 'malloc'
> > What version is this? I can't see any malloc on line 205 in easy.c
> > any
> > recent version...
> > And anyway, this is not a problem with libcurl as I see it. It is
> > some kind of
> > restriction malloc that VS seems to impose. I honestly don't
> > understand the
> > warning!
> I may have added a few blank lines and messed up the line numbers.
> These lines in easy.c (version 7.17.0):
> * If a memory-using function (like curl_getenv) is used before
> * curl_global_init() is called, we need to have these pointers set
> curl_malloc_callback Curl_cmalloc = (curl_malloc_callback)malloc;
> curl_free_callback Curl_cfree = (curl_free_callback)free;
> curl_realloc_callback Curl_crealloc = (curl_realloc_callback)realloc;
> curl_strdup_callback Curl_cstrdup =
> curl_calloc_callback Curl_ccalloc = (curl_calloc_callback)calloc;
I have found out why the library was crashing when using the Release
runtime libraries. The problem was a char * allocation that didn't
include space for the trailing \0 character. The debug libraries were
working ok because of the \0 padding (to check for buffer overruns) but
it wasn't reported by memory tools since there were no writes past the
last valid character. The first \0 from the padding was treated as part
of the string when in Debug mode but in Release mode that character was
not available - crash.
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Received on 2007-11-06