From: Florian Weimer <fweimer@redhat.com>
To: "H.J. Lu via Libc-alpha" <libc-alpha@sourceware.org>
Cc: Andreas Schwab <schwab@linux-m68k.org>, "H.J. Lu" <hjl.tools@gmail.com>
Subject: Re: [PATCH v2] x86-64: Align child stack to 16 bytes [BZ #27902]
Date: Mon, 24 May 2021 14:07:18 +0200 [thread overview]
Message-ID: <87lf842v49.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <CAMe9rOopEdoNi2dDRMN-DaLC=SyKrJoFgxOZFOzz7oDUY18fHA@mail.gmail.com> (H. J. Lu via Libc-alpha's message of "Sun, 23 May 2021 11:40:50 -0700")
* H. J. Lu via Libc-alpha:
> +static int
> +f (void *arg)
> +{
> + bool ok = true;
> +
> + puts ("in f");
> +
> + if (TEST_STACK_ALIGN ())
> + ok = false;
> +
> + return ok ? 0 : 1;
> +}
Is it okay to call libc functions from the callback because it is after
a fork-style clone (without any flags) that inherits the TCB? Otherwise
there are going to be problems with the stack protector at least.
> + char st[STACK_SIZE + 1];
> + /* NB: Align child stack to 1 byte. */
> + char *stack = PTR_ALIGN_UP (&st[0], 2) + 1;
> +
> +#ifdef __ia64__
> + extern int __clone2 (int (*__fn) (void *__arg), void *__child_stack_base,
> + size_t __child_stack_size, int __flags,
> + void *__arg, ...);
> + pid_t p = __clone2 (f, stack, STACK_SIZE, 0, 0);
> +#else
> +# if _STACK_GROWS_DOWN
> + pid_t p = clone (f, stack + STACK_SIZE, 0, 0);
> +# elif _STACK_GROWS_UP
> + pid_t p = clone (f, stack, 0, 0);
> +# else
> +# error "Define either _STACK_GROWS_DOWN or _STACK_GROWS_UP"
> +# endif
> +#endif
I think the (mis)alignment step has to be among the
_STACK_GROWS_UP/_STACK_GROWS_DOWN part.
Thanks,
Florian
next prev parent reply other threads:[~2021-05-24 12:07 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-23 17:29 [PATCH] x86-64: Align child stack to 16 bytes H.J. Lu
2021-05-23 17:57 ` Andreas Schwab
2021-05-23 18:40 ` [PATCH v2] x86-64: Align child stack to 16 bytes [BZ #27902] H.J. Lu
2021-05-24 12:07 ` Florian Weimer [this message]
2021-05-24 12:53 ` H.J. Lu
2021-05-24 14:19 ` Carlos O'Donell
2021-05-24 14:55 ` Noah Goldstein
2021-05-24 18:46 ` H.J. Lu
2021-05-24 18:46 ` H.J. Lu
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