Date: Fri, 17 Apr 2015 16:23:33 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [PATCH] replace 'hlt' by 'ud2' in i386/x32/x86_64 a_crash implementations On Fri, Apr 17, 2015 at 09:48:38PM +0300, Alexander Monakov wrote: > > > An argument in favor of plain hlt/ud2 is that registers and memory are > > > preserved, in case someone will be analyzing the coredump. > > > > That's a good point. The above could be fixed to preserve registers > > with some minor added push/pop (simple pusha/popa on 32-bit) > > before/after the syscall, but then it gets bigger. > > Hm, no, I wouldn't like to see that. By the time a_crash executes, "the > impossible happened", so stack pointer might be pointing somewhere you > wouldn't want modified. Given that it's used in C code and C code generally can't be running at all without a stack, I don't think that's an issue. We're not using it for detection of stack overflows (which are handled with guard pages) but for detection of corrupt heap structures, etc. It's possible that a heap overflow could cause the stack pointer to be restored to the wrong value, but then I think you would have a really hard time reaching the a_crash() call. > A good reason for compilers to generate ud2 is that it also works for kernel > code, unlike hlt -- but then OSv carries a copy of musl to run it in the > context of, as I understand, virtualized kernel -- what happens when they > execute a_crash? Yes, that does seem like a good aspect. Rich
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