Re: Net-SNMP v5.8 and Darwin

Bart,
I was hoping to discuss with you on IRC; but, you're not online.

On Sun, Apr 22, 2018, at 4:10 PM, Bart Van Assche wrote:
> On 04/22/18 08:35, Keith Mendoza wrote:
> > Bart,
> > I was actually working on this yesterday. This is what I know so far after a few hours of digging into this: It appears that there's an issue with getting to the memory address that EVP_sha512() returns when it's called in sc_get_openssl_hashfn(). Why this is so, I don't know. Below are details of what I've figured out so far:
> > 
> > On my environment, I'm using OpenSSL 1.0.2o installed using mac ports. EVP_sha512() simply returns the address of a static const struct env_md_st instance once you expand the EVP_MD typedef (see the source here: https://github.com/openssl/openssl/blob/3ce7bc40a3c48da1c96c2d04c10045bd797c6aa3/crypto/evp/m_sha1.c#L216). When I was stepping through using the lldb debugger, when I inspect the value of hashfn after the call to EVP_sha512() it actually reports an error that the address is inaccessible. That one's got me stumped. In line 192, the call EVP_DigestInit() happens and the address returned by EVP_sha512() is passed as the 2nd parameter to that function. Kaboom for obvious reasons.
> > 
> > I'm no expert on the rules of accessing memory space from dynamic libraries. Hopefully, someone else can chime in. My next step  is to write a small test program to isolate the digest initialization code to see if I can replicate the issue outside of Net-SNMP.
> 
> Hello Keith,
> 
> Can you have a look at the openssl/evp.h header file? The following 
> warning appears in the OS/X build output, which is suspicious:
> 
> 
> scapi.c:88:12: warning: implicit declaration of function 'EVP_sha224' is 
> invalid in C99 [-Wimplicit-function-declaration]
>      return EVP_sha224();
>             ^

I actually stumbled on include/net-snmp/system/darwin*.h files while figuring out why things are crashes when I thought that EVP_DigestInit() wanted a function pointer. I've used EVP_DigestInit_ex() in the past which would normally pass the address of EVP_*() functions as it's 3rd parameter. Since I wanted to assign the address of the functions in sc_get_openssl_hashfn() I got an undeclared error. Based on the comments on those files it feels like making sure that Net-SNMP doesn't try to use functions that are not present in the OpenSSL version available for the given macOS versions, I feel that should have been a function check in automake and sc_get_openssl_hashfn() whould have #ifdef HAVE_<funcname> on them instead.

On another note, I thought that Net-SNMP has to use C89 thanks to Microsoft deciding they're not going to support anything past that? I feel mixing C versions between targets could cause us maintenance issues.

> 
> Thanks,
> 
> Bart.

This is what I'm going to do: I'm going to add --with-cflags='-std=c89' in configureu and see if we stumbled on something that clang does differently with the ABI when its compiling in C99 vs C89.

-- 
Thanks,
Keith (pantherse)

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