Re: Strange Segfault with V 0.9.3 an MinGW Cross Compile

[g4-lisz@xxxxxxxxxxxx]

Hi,

On 15.01.20 10:02, Skalák, Zdeněk wrote:

> Hello,
>
> On Wed, Jan 15, 2020 at 9:48 AM <g4-lisz@xxxxxxxxxxxx
> <mailto:g4-lisz@xxxxxxxxxxxx>> wrote:
>
>     On 15.01.20 08:27, Andreas Schneider wrote:
>
>     > On Wednesday, 15 January 2020 01:22:13 CET g4-lisz@xxxxxxxxxxxx
>     <mailto:g4-lisz@xxxxxxxxxxxx> wrote:
>     >> I cross compiled V 0.9.3 with MinGW on Ubuntu. The compilation
>     worked
>     >> flawlessly.
>     >>
>     >> But when I run my code linked to the resulting libssh.dll, it
>     crashes
>     >> immediately when I set verbosity to > 2.
>     >>
>     >> I could track this down to vsnprintf() which is called through
>     line 865
>     >> in channels.c:
>     >>
>     >>   SSH_LOG(SSH_LOG_PACKET,
>     >>           "placing %zu bytes into channel buffer (%s)",
>     >>           len,
>     >>           s_stderr ? "stderr" : "stdout");
>     > Try s_stderr -> is_stderr
>
>     Hi Andreas,
>
>     Haha that would be a silly issue, when the compiler would not complain
>     about this...
>
>     Sorry, I somehow lost the 'i' when I pasted the code into the mail.
>
>
>
> I can imagine two things which could went wrong:
> a) libstdc (or whomever implements the vsnprintf()) doesn't know the
> `%zu` format, so this one is skipped and the `len` argument is used
> for the (%s) format
> b) 32/64 bit mismatch - the format (count of bytes) of the `len` on
> the stack doesn't correspond to the format (count of bytes) of the
> `%zu` specifier, so for the second (%s) format, some `grabage from the
> stack` is used
>
> Both these two scenarios can lead to mysterious crashes ....

Thanks a lot for your thoughts! Indeed it was a).

I realized that when after my "partch" (removing %s and the second
argument), `zu` was printed instead of the length...

I sent a real patch (Use inttypes macros for size_t format string).

Best regards,
Till