Re: [PATCH 5/7] configure: Unnest detection of -z,relro and -z,now

[Richard Henderson]

On 12/17/19 10:11 PM, Thomas Huth wrote:
>> +# Detect support for DT_BIND_NOW.
>> +if compile_prog "" "-Wl,-z,now" ; then
>> +  LDFLAGS="-Wl,-z,now $LDFLAGS"
>> +fi
>> +
>> +# Detect support for PT_GNU_RELRO.
>> +if compile_prog "" "-Wl,-z,relro" ; then
>> +  LDFLAGS="-Wl,-z,relro $LDFLAGS"
>> +fi
> 
> Looking at
> https://mudongliang.github.io/2016/07/11/relro-a-not-so-well-known-memory-corruption-mitigation-technique.html
> the idea of specifying these two options together was likely to get
> "Full RELRO" instead of only "Partial RELRO".

Sure.

> Thus, does it make sense to have "-Wl,-z,now" without "-Wl,-z,relro" in
> QEMU? Or should this rather check whether both are possible, then use
> both, otherwise just try to use "relro" alone?

Honestly, I expect them both to be supported in any binutils.

I split the two tests just because they didn't seem to be logically connected.
 But I had forgotten about, or perhaps never heard, the terms "full" and
"partial" relro.

I can put them back together with an appropriate comment it you like.  One less
thing to run during configure...


r~