On Sat, Jun 17, 2017 at 12:58:03PM +0100, Stuart Henderson wrote: > On 2017/06/04 04:40, Bryan Steele wrote: > > "As Shmuel reported in > > <https://gcc.gnu.org/ml/gcc-help/2017-03/msg00009.html>, > > on x86-64 small structures in automatic storage are aligned to 16 bytes. > > This seems to be because of a mix-up between bits and bytes in the i386 > > target code. > > > > * config/i386/i386.c (ix86_local_alignment): Align most aggregates > > of 16 bytes and more to 16 bytes, not those of 16 bits and more." > > > > https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=b44e9be23d38be8997ae64d7509ac22cb4c556d6 > > > > It might be worth fixing this in ports gcc 4.9, found by tedu@ in 2014 > > and committed by martynas@ to base gcc4 shortly later. > > > > http://www.tedunangst.com/flak/post/my-stack-protector-wasnt-working > > http://marc.info/?l=openbsd-cvs&m=139895377300712&w=2 > > http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/gnu/gcc/gcc/config/i386/i386.c.diff?r1=1.3&r2=1.4&f=h > > Does this actually work? > > I might be missing something from this, but I haven't been able to > elicit a SIGABRT from Ted's simple test program with any of the > compilers. > > Any idea what's going on? > > $ for i in gcc egcc /usr/bin/clang /usr/local/bin/clang; do printf "$i\t"; $i > -o scanf scanf.c; echo 12345678901234567890123456789012 | ./scanf; done > gcc 12345678901234567890123456789012 0xabad1dea > egcc 12345678901234567890123456789012 0xabad1dea > /usr/bin/clang 12345678901234567890123456789012 0xabad1dea > /usr/local/bin/clang 12345678901234567890123456789012 0xabad1dea
It works with the example I gave previously, at least, I can't find tedu@'s example, but there is always the possibility for alignment or padding differences preventing it from reproducibly triggering on every overflow. http://marc.info/?l=openbsd-ports&m=149667837410983&w=2 $ pkg_info | grep gcc gcc-4.9.4p5 GNU compiler collection: core C compiler $ egcc ssp-test.c -o ssp-test-egcc $ ./ssp-test-egcc Abort trap Of course, there could *always* be more compiler bugs.. ;-) -Bryan.
