From mboxrd@z Thu Jan 1 00:00:00 1970 From: viro@ZenIV.linux.org.uk (Al Viro) Date: Mon, 15 Oct 2012 17:27:32 +0100 Subject: [revert request for commit 9fff2fa] Re: [git pull] signals pile 3 In-Reply-To: <20121015160710.GC30907@arm.com> References: <20121013005334.GM2616@ZenIV.linux.org.uk> <507ADBBB.9090209@gmail.com> <20121014164020.GV2616@ZenIV.linux.org.uk> <20121014172640.GW2616@ZenIV.linux.org.uk> <20121014192402.GZ2616@ZenIV.linux.org.uk> <20121014195611.GA2616@ZenIV.linux.org.uk> <20121015160710.GC30907@arm.com> Message-ID: <20121015162732.GG2616@ZenIV.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Oct 15, 2012 at 05:07:10PM +0100, Catalin Marinas wrote: > On Sun, Oct 14, 2012 at 08:56:11PM +0100, Al Viro wrote: > > On Sun, Oct 14, 2012 at 08:24:03PM +0100, Al Viro wrote: > > > > > Russell, could you recall what those had been about? I'm not sure if that > > > had been oopsable that far back (again, oops scenario is userland stack > > > page getting swapped out before we get to start_thread(), leading to > > > direct read from an absent page in start_thread() by plain ldr, without > > > anything in exception table about that insn), but it looks very odd > > > regardless of that problem. > > > > BTW, arm64 has copied that logics, so it also seems to be unsafe and very > > odd - there we definitely have only ELF to cope with. arm64 folks Cc'd... > > Good point. We don't need this on arm64 and probably neither on arm (at > least since EABI). > > Setting x0 may cause other issues as well. The dynamic loader simply > ignores the startup registers but for static binaries the _start code in > glibc expects r0 to contain a function pointer to be registered with > atexit() in __libc_start_main() or NULL. Since we pass argc in there, > for static binaries the rtld_fini argument to __libc_start_main() is > neither NULL nor something meaningful. The value left there by start_thread() will not reach the userland anyway...