On Mon, 2021-02-22 at 10:50 +0100, Gabriel Ravier via Gcc wrote: > On 2/22/21 10:37 AM, Michael J. Baars wrote: > > On Mon, 2021-02-22 at 01:29 -0800, Andrew Pinski wrote: > > > On Mon, Feb 22, 2021 at 1:17 AM Michael J. Baars > > > <mjbaars1977....@cyberfiber.eu> wrote: > > > > Hi, > > > > > > > > I just wrote this little program to demonstrate a possible flaw in both > > > > malloc and calloc. > > > > > > > > If I allocate a the simplest memory region from main(), one out of > > > > three optimization flags fail. > > > > If I allocate the same region from a function, three out of three > > > > optimization flags fail. > > > > > > > > Does someone know if this really is a flaw, and if so, is it a gcc or a > > > > kernel flaw? > > > There is no flaw. GCC (kernel, glibc) all assume unaligned accesses > > > on x86 will not cause an exception. > > Is this just an assumption or more like a fact? I agree with you that byte > > aligned is more or less the same as unaligned. > IIRC it's a fact, unless you change EFLAGS to enable the unaligned > access exception flag, which is forbidden by the ABI.
I see :) > > > Thanks, > > > Andrew > > > > > > > Regards, > > > > Mischa.
