On Sun, 29 Oct 2023 16:24:02 +0100
Otto Moerbeek <otto@drijf.net> wrote:
> On Sun, Oct 29, 2023 at 08:13:43AM -0400, Brad Smith wrote:
> > The existing Boost::Context diffs do not apply as is, there were some changes there.
> > Someone more familiar with this neeeds to look at what needs to be done for i386.
> >
> > https://github.com/boostorg/context/commit/2f0b5034b72cbb858849bd744ffb06df04521e5a
>
> This one is a bit surprising. PowerDNS Recursor has been compiled with
> -fstack-protector for ages, and has no issues with the existing
> (patched to conform to out calling conventions) context switch
> assembly in boost 1.80 on i386.
>
> I'm setting up a i386 VM to check things further. I imagine we might
> be able to take the easy way and continue to use the asm from the 1.80
> port in boost 1.83.
>
> -Otto
The old asm might work. The changes in the new asm seem specific to
Linux (and maybe Hurd), where gcc -fstack-protector gets its cookie from
thread-local storage. This cookie is "uintptr_t stack_guard" in
glibc [1] and "uintptr_t canary" in musl libc [2]. The same offset in
OpenBSD <tib.h> "struct tib" doesn't have a cookie.
By my guess, the new asm is also useless on Linux. All threads in one
process share the same cookie [3]. The new asm to save and restore the
cookie would have no effect. PowerDNS Recursor with -fstack-protector
should always have worked with old Boost, including on Linux.
--gkoehler
[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86_64/nptl/tls.h;h=1403f939f7e5a81aeabf58aefac011dd3ce14de6;hb=HEAD#l51
[2] https://git.musl-libc.org/cgit/musl/blame/src/internal/pthread_impl.h#n31
[3] https://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/pthread_create.c;h=6a41d50109cb27ecc09e56ced4745b7f83c06e07;hb=HEAD#l705
No comments:
Post a Comment