POSIX Port: Round up stack sizes correctly on macOS

[hollinsky]

Description

On macOS, pthread_attr_setstacksize requires the stack size to be a multiple of the system page size.

The previous changes here assumed the use of pthread_attr_setstack, however the transition to pthread_attr_setstacksize means we can avoid rounding the pxEndOfStack pointer.

This is additionally positive because pxEndOfStack was actually being rounded in the wrong direction -- it ought to have been rounded down (_trunc) instead of up due to the stack growth direction. In my case this actually caused pxEndOfStack to end up after pxTopOfStack, which underflowed and created a huge stack size request + EXC_BAD_ACCESS in pthread_create.

Test Steps

I had a task with a 4kb stack which was causing the issue. Simply xTaskCreate with a 4kb stack on macOS and it will crash.

Checklist:

• I have tested my changes. No regression in existing tests.
• I have modified and/or added unit-tests to cover the code changes in this Pull Request.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[aggarg]

Thank you for pointing this. Given that we are no longer using pthread_attr_setstack to use the application supplied memory as stack, I wonder if we should even call pthread_attr_setstacksize. May be can leave stack size to the default OS setting and can simplify the code like the following:

StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
                                     StackType_t * pxEndOfStack,
                                     TaskFunction_t pxCode,
                                     void * pvParameters )
{
    Thread_t * thread;
    pthread_attr_t xThreadAttributes;
    int iRet;

    ( void ) pthread_once( &hSigSetupThread, prvSetupSignalsAndSchedulerPolicy );

    /*
     * Store the additional thread data at the start of the stack.
     */
    thread = ( Thread_t * ) ( pxTopOfStack + 1 ) - 1;
    pxTopOfStack = ( StackType_t * ) thread - 1;

    thread->pxCode = pxCode;
    thread->pvParams = pvParameters;
    thread->xDying = pdFALSE;

    pthread_attr_init( &xThreadAttributes );

    thread->ev = event_create();

    vPortEnterCritical();

    iRet = pthread_create( &thread->pthread, &xThreadAttributes,
                           prvWaitForStart, thread );

    if( iRet != 0 )
    {
        prvFatalError( "pthread_create", iRet );
    }

    vPortExitCritical();

    return pxTopOfStack;
}

What do you think?

[aggarg]

@hollinsky Can you check if the above addresses the issue you are facing?