[EXT] Re: [PATCH v2] lib/cryptodev: fix assertion to remove GCC compilation warning

[Akhil Goyal]

> On Mon, 22 May 2023 15:04:52 -0400
> Kamil Godzwon <kamilx.godzwon at intel.com> wrote:
> 
> > /home/vagrant/dpdk/build/include/rte_crypto_sym.h:1009:4: \
> > warning: Value stored to 'left' is never read [deadcode.DeadStores]
> >                           left = 0;
> >                           ^      ~
> >   1 warning generated.
> >
> > Compilator sees that the variable 'left' is never read after
> > assignment a '0' value. To get rid of this warning message, use 'if'
> > condition to verify the 'left' value before RTE_ASSERT.
> >
> > Signed-off-by: Kamil Godzwon <kamilx.godzwon at intel.com>
> > ---
> > v2:
> > Changed commit message as the line was too long
> > Removed braces
> > ---
> >  lib/cryptodev/rte_crypto_sym.h | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/cryptodev/rte_crypto_sym.h b/lib/cryptodev/rte_crypto_sym.h
> > index b43174dbec..dcef1a5049 100644
> > --- a/lib/cryptodev/rte_crypto_sym.h
> > +++ b/lib/cryptodev/rte_crypto_sym.h
> > @@ -1016,7 +1016,9 @@ rte_crypto_mbuf_to_vec(const struct rte_mbuf
> *mb, uint32_t ofs, uint32_t len,
> >  		left -= seglen;
> >  	}
> >
> > -	RTE_ASSERT(left == 0);
> > +	if (left != 0)
> > +		RTE_ASSERT(false);
> > +
> >  	return i;
> >  }
> >
> 
> This could happen if the passed in length to this routine was larger than
> the amount of data in the mbuf. Should the function check and return an error?
> 
> Panic should only be reserved for seriously corrupted input (like invalid mbuf).
> 
> Also, this is a big enough function that it really should not be inlined.

This is a datapath API. RTE_ASSERT is normally not enabled in release build.
So, this assert is not doing any check for normal scenario.
We normally avoid these type of error checks in the datapath.
And while building in debug mode, we need these asserts to give a backtrace also
To debug the rootcause of the issue.

I would suggest fixing the assert itself instead of adding a check.
Current patch will affect performance.

Agreed, that the function is big for being an inline function,
but that is what all the datapath APIs are and
we keep them inline to improve the performance.