Re: [LTP] ltp_clone alignment issues.

Hannu Heikkinen
2010-10-01T04:06:23Z

On 30/09/10 12:42 +0200, Carmelo AMOROSO wrote:
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> On 9/30/2010 3:31 PM, Hannu Heikkinen wrote:
> > On 29/09/10 15:34 +0200, ext Carmelo AMOROSO wrote:
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> > > On 9/27/2010 3:34 PM, Carmelo AMOROSO wrote:
> > > > Folks,
> > > > I want to reopen an old discussion on ltp_clone and stack alignment
> > > > issue (see
> > > >
> > http://sourceforge.net/mailarchive/message.php?msg_name=4B421480.1040400%40petalogix.com).
> > > > Indeed recently a commit has partially fixed a problem on ARM
> > > > (0056e395170eb8fc3ffbb22d7bd364fe47c2013e), but I think this should be
> > > > extended to all archs that have stack that grows downwards.
> > > >
> > > > Indeed, as Jiri replied in that old thread, the value passed to clone as
> > > > child stack should be never accessed, because it is the topmost address
> > > > of the memory allocated for the child process (it's the previous stack
> > > > pointer).
> > > >
> > > > So, in archs that do not like unaligned stack, using (stack - size - 1 )
> > > > will cause the process to be killed by a SIGBUS, on other archs, we are
> > > > just wasting one byte of the malloc-ed stack.
> > > >
> > > > On my SH4 arch, the stack must be 4byte aligned (as in ARM).
> > > >
> > > > Please, find attached a patch against master branch
> > > >
> > > > Best regards,
> > > > Carmelo
> > >
> > > Hi,
> > > any feedback on this ?
> > >
> > > Cheers,
> > > Carmelo
> >
> > >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> > Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>
> > ---
> > lib/cloner.c | 9 +++------
> > 1 files changed, 3 insertions(+), 6 deletions(-)
> >
> > diff --git a/lib/cloner.c b/lib/cloner.c
> > index 6ad4a00..e53c9cf 100644
> > --- a/lib/cloner.c
> > +++ b/lib/cloner.c
> > @@ -59,16 +59,13 @@ ltp_clone(unsigned long clone_flags, int (*fn)(void
> > *arg), void *arg,
> > ret = clone(fn, stack, clone_flags, arg);
> > #elif defined(__ia64__)
> > ret = clone2(fn, stack, stack_size, clone_flags, arg, NULL, NULL,
> > NULL);
> > -#elif defined(__arm__)
> > +#else
> > /*
> > - * Stack size should be a multiple of 32 bit words
> > - * & stack limit must be aligned to a 32 bit boundary
> > + * For archs where stack grows downwards, stack points to the topmost
> > address
> > + * of the memory space set up for the child stack.
> > */
> > ret = clone(fn, (stack ? stack + stack_size : NULL),
> > clone_flags, arg);
> > -#else
> > - ret = clone(fn, (stack ? stack + stack_size - 1 : NULL),
> > - clone_flags, arg);
> > #endif
> >
> > return ret;
> > --
> > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> >
> > Hi,
> >
> > Acked-by Hannu Heikkinen <ext-hannu.m.heikkinen@nokia.com>
> >
> > Br,
> > Hannu
> >
> > --
> > Hannu Heikkinen
> > http://www.nixu.com
> >
>
> Thanks, Hannu
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Hi,

I was thinking your patch once again, and I think it would be wiser if
we would have something like:

--- ../tmp2/ltp-full-20100630/lib/cloner.c 2010-07-03 21:29:04.000000000
+0300
+++ lib/cloner.c 2010-09-03 14:48:20.000000000 +0300
@@ -43,6 +43,16 @@
pid_t *parent_tid, void *tls, pid_t *child_tid);
#endif

+/*
+ * Most arch really want to have stack aligned to some sane boundary.
+ */
+#ifdef __arm__
+#define ALIGN_STACK(stack) \
+ ((void *)(((unsigned long)stack) & ~((sizeof(void *)) - 1)))
+#else
+#define ALIGN_STACK(stack) (stack)
+#endif
+
/***********************************************************************
* ltp_clone: wrapper for clone to hide the architecture dependencies.
* 1. hppa takes bottom of stack and no stacksize (stack grows up)
@@ -60,7 +70,7 @@
#elif defined(__ia64__)
ret = clone2(fn, stack, stack_size, clone_flags, arg, NULL, NULL,
NULL);
#else
- ret = clone(fn, (stack ? stack + stack_size - 1 : NULL),
+ ret = clone(fn, (stack ? ALIGN_STACK(stack + stack_size - 1) : NULL),
clone_flags, arg);
#endif

The above patch iis in use in our ARM based LTP test suite. Note that -1 is
needed for not clobbering eg possibly malloced area after child stack.
Could u please change that prev patch a bit, for ensuring that child stack
is in proper size etc. Above patch is not sufficient, because ALIGN_STACK
in that is only used for arm archs.

br,
Hannu

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