[PATCH v2 1/3] score: Enforce stack and TLS alignment

[Kinsey Moore]

-----Original Message-----
From: Sebastian Huber <sebastian.huber at embedded-brains.de>
Sent: Tuesday, March 2, 2021 15:09
To: Kinsey Moore <kinsey.moore at oarcorp.com>; devel at rtems.org
Subject: Re: [PATCH v2 1/3] score: Enforce stack and TLS alignment


> On 02/03/2021 20:47, Kinsey Moore wrote:
>> Enforce alignment of the stack begin and end by allocating enough stack
>> area that the desired size can be aligned to CPU_STACK_ALIGNMENT. This
>> also ensures that the space reserved for TLS data falls on stack
>> alignment boundaries which satisfies TLS alignment requirements.
>> ---
>>   cpukit/rtems/src/taskcreate.c       |  5 ++++-
>>   cpukit/score/src/threadinitialize.c |  8 +++++---
>>   cpukit/score/src/tlsallocsize.c     | 22 ++++++++++++++--------
>>   3 files changed, 23 insertions(+), 12 deletions(-)
>>
>> diff --git a/cpukit/rtems/src/taskcreate.c b/cpukit/rtems/src/taskcreate.c
>> index c065a159c6..bad13cb532 100644
>> --- a/cpukit/rtems/src/taskcreate.c
>> +++ b/cpukit/rtems/src/taskcreate.c
>> @@ -53,8 +53,11 @@ static rtems_status_code _RTEMS_tasks_Allocate_and_prepare_stack(
>>     thread_config->stack_free = _Stack_Free;
>>     size = _Stack_Ensure_minimum( config->storage_size );
>>     size = _Stack_Extend_size( size, thread_config->is_fp );
>> +  size = RTEMS_ALIGN_UP( size, CPU_STACK_ALIGNMENT );
>
> This can overflow. It needs to move into _Stack_Extend_size() which
> performs overflow handling. I think we need the following invariants
> which should be checked by static assertions (if not already done):
>
> CPU_STACK_ALIGNMENT is a power of two
>
> CPU_HEAP_ALIGNMENT is a power of two
>
> CPU_STACK_ALIGNMENT >= CPU_HEAP_ALIGNMENT
>
> The _Stack_Extend_size() should add CPU_STACK_ALIGNMENT - 1 to the size.

I don't see that _Stack_Extend_size() does any overflow handling. Should it? Mathematical overflow is a possibility, but I'd expect to see problems attempting the allocation long before that since it's just pulling from the workspace area of the heap.

Kinsey