On Sat, Aug 05, 2017 at 02:21:55AM -0400, Mark H Weaver wrote:
> Reviving a very old thread...
>
> l...@gnu.org (Ludovic Courtès) writes:
>
> > Efraim Flashner <efr...@flashner.co.il> skribis:
> >
> >> man2 clone: EINVAL: ... on aarch64, child_stack must be a multiple of 16.
> >>
> >> * nix/libstore/build.cc (DerivationGoal::startBuilder): When on aarch64,
> >> when calling clone(), increment the stack by 16.
> >> ---
> >> nix/libstore/build.cc | 7 ++++++-
> >> 1 file changed, 6 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
> >> index cebc404d1..362b2d91d 100644
> >> --- a/nix/libstore/build.cc
> >> +++ b/nix/libstore/build.cc
> >> @@ -2008,7 +2008,12 @@ void DerivationGoal::startBuilder()
> >> char stack[32 * 1024];
> >> int flags = CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWIPC | CLONE_NEWUTS |
> >> SIGCHLD;
> >> if (!fixedOutput) flags |= CLONE_NEWNET;
> >> - pid = clone(childEntry, stack + sizeof(stack) - 8, flags, this);
> >> +// if statements are hard, fix this
> >> +//#if __AARCH64__
> >> + pid = clone(childEntry, stack + sizeof(stack) - 16, flags, this);
> >> +//#else
> >> +// pid = clone(childEntry, stack + sizeof(stack) - 8, flags, this);
> >> +//#endif
> >
> > I think we can make it unconditional. Could you test whether the
> > attached patch works for aarch64?
> >
> > Thanks!
> >
> > Ludo’.
> >
> > diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
> > index cebc404d1..9b7bb5391 100644
> > --- a/nix/libstore/build.cc
> > +++ b/nix/libstore/build.cc
> > @@ -26,6 +26,7 @@
> > #include <errno.h>
> > #include <stdio.h>
> > #include <cstring>
> > +#include <stdint.h>
> >
> > #include <pwd.h>
> > #include <grp.h>
> > @@ -2008,7 +2009,11 @@ void DerivationGoal::startBuilder()
> > char stack[32 * 1024];
> > int flags = CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWIPC | CLONE_NEWUTS |
> > SIGCHLD;
> > if (!fixedOutput) flags |= CLONE_NEWNET;
> > - pid = clone(childEntry, stack + sizeof(stack) - 8, flags, this);
> > +
> > + /* Ensure proper alignment on the stack. On aarch64, it has to be 16
> > + bytes. */
> > + pid = clone(childEntry, (char *)(((uintptr_t)stack + 16) & ~0xf),
> > + flags, this);
> > if (pid == -1)
> > throw SysError("cloning builder process");
> > } else
>
> This patch, applied in February, contains a serious error. The stack
> address passed to 'clone' is supposed to be near the end of the memory
> block allocated for the stack, and that's how it was before this patch
> was applied. Since this patch was applied, it now passes an address
> very close to the *start* of the memory block.
>
> This broke the daemon on mips64el in a subtle way that was rather
> difficult to debug. After about six months of being too busy with other
> things to investigate properly, I finally tracked it down to this
> change.
>
> I reverted this commit. Let's try again to find a proper fix for this
> issue on aarch64.
>
> Thanks,
> MarkHow about doubling the size of the stack to [32 * 1024 * 2] and changing the clone location to 'stack + sizeof(stack) - 16', does that work for mips64el? With this revert the daemon is completely broken on aarch64. -- Efraim Flashner <efr...@flashner.co.il> אפרים פלשנר GPG key = A28B F40C 3E55 1372 662D 14F7 41AA E7DC CA3D 8351 Confidentiality cannot be guaranteed on emails sent or received unencrypted
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