Re: [HACKERS] SerializedSnapshotData alignment

On Mon, Feb 27, 2017 at 2:18 PM, Noah Misch <noah@leadboat.com> wrote:
> I wondered the same thing; if nothing else, why don't protosciurus and
> castoroides fail the same way?  They do use older compilers, "Sun C 5.10
> SunOS_sparc 2009/06/03" and gcc 3.4.3.  I have "Sun C 5.12 SunOS_sparc
> 2011/11/16" and gcc 4.9.2, both of which are alignment-sensitive in several
> configurations, according to the attached test program.  However, in a 32-bit
> build with this Sun C, I don't get alignment-related bus errors.  (Those
> animals build 64-bit, so this isn't the full story.)

It's been a while but I seem to recall that Sun C defaulted to a
-xmemalign setting that tolerated misaligned reads in 32 bit builds,
but used a different default on 64 bit builds.  "Solaris Application
Programming" 5.8.5 seems to confirm this:  "For 32-bit applications,
since Sun Studio 9, the default is for the compiler to assume 8-byte
alignment and to trap and correct any misaligned data accesses.  For
64-bit applications, the compiler assumes 8-byte alignment, but the
application will SIGBUS on a misaligned access."

Yet castoroides seems to be building with -m64, so that's not the
explanation.  Could it be correctly aligned by coincidence?

-- 
Thomas Munro
http://www.enterprisedb.com