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Re: [PATCH][BZ #11787] Fix stack guard size accounting
- From: Szabolcs Nagy <szabolcs dot nagy at arm dot com>
- To: Florian Weimer <fweimer at redhat dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Cc: nd at arm dot com
- Date: Wed, 20 Dec 2017 14:55:07 +0000
- Subject: Re: [PATCH][BZ #11787] Fix stack guard size accounting
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On 20/12/17 13:09, Florian Weimer wrote:
> On 12/12/2017 03:21 PM, Szabolcs Nagy wrote:
>> Previously if user requested S stack and G guard when creating a
>> thread, the total mapping was S and the actual available stack was
>> S - G - static_tls, which is not what the user requested.
>> This patch fixes the guard size accounting by pretending the user
>> requested S + G stack. This way all later logic works out except
>> when reporting the user requested stack size (pthread_getattr_np)
>> or when computing the minimal stack size (__pthread_get_minstack).
>> Normally this will increase thread stack allocations by one page.
>> TLS accounting is not affected, that will require a separate fix.
> Should this fix use a separate bug number?
i can open a separate bug.
>> 2017-12-12 Szabolcs Nagy<firstname.lastname@example.org>
>> [BZ #11787]
>> * nptl/allocatestack.c (allocate_stack): Add guardsize to stacksize.
>> * nptl/nptl-init.c (__pthread_get_minstack): Remove guardsize from
>> * nptl/pthread_getattr_np.c (pthread_getattr_np): Likewise.
> Patch looks good in general. The computation for stackblock_size looks right to me.
>> diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
>> index 1cc789319564b468cf07bdb1304b27dc5a91e86f..9525322b1f92bb34aa21dcab28566aecd7434e90 100644
>> --- a/nptl/allocatestack.c
>> +++ b/nptl/allocatestack.c
>> @@ -532,6 +532,7 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
>> /* Make sure the size of the stack is enough for the guard and
>> eventually the thread descriptor. */
>> guardsize = (attr->guardsize + pagesize_m1) & ~pagesize_m1;
>> + size += guardsize;
>> if (__builtin_expect (size < ((guardsize + __static_tls_size
>> + MINIMAL_REST_STACK + pagesize_m1)
>> & ~pagesize_m1),
> I wonder if we should add an overflow check there and return EINVAL if
> guardsize < attr->guardsize || size + guardsize < guardsize
but i saw several overflowing arithmetics around stack computation.