libthr and main thread stack size

[Julian Elischer]

On 9/20/14, 3:27 AM, John Baldwin wrote:
> On Tuesday, September 16, 2014 11:13:24 AM Konstantin Belousov wrote:
>> On Mon, Sep 15, 2014 at 03:47:41PM -0600, Justin T. Gibbs wrote:
>>> On Aug 8, 2014, at 5:22 AM, Konstantin Belousov <kostikbel at gmail.com>
>>> wrote:
>>>
>>> ?
>>>
>>>> Below is the patch which adds environment variable
>>>> LIBPTHREAD_BIGSTACK_MAIN. Setting it to any value results in the
>>>> main thread stack left as is, and other threads allocate stack
>>>> below the area of RLIMIT_STACK. Try it. I do not want to set this
>>>> behaviour as default.
>>> Is there a reason this should not be the default? Looking at the
>>> getrlimit() page on the OpenGroup?s site they say:
>>>
>>> RLIMIT_STACK This is the maximum size of the initial thread's stack,
>>> in bytes. The implementation does not automatically grow the stack
>>> beyond this limit. If this limit is exceeded, SIGSEGV shall be
>>> generated for the thread. If the thread is blocking SIGSEGV, or the
>>> process is ignoring or catching SIGSEGV and has not made arrangements
>>> to use an alternate stack, the disposition of SIGSEGV shall be set to
>>> SIG_DFL before it is generated.
>>>
>>> Does posix say something different?
>>>
>>> I ran into this issue when debugging a segfault on Postgres when
>>> running an (arguably quite bogus) query that should have fit within
>>> both the configured stack rlimit and Postgres? configured stack limit.
>>> The Postgres backend is really just single threaded, but happens
>>> to pull in libpthread due to the threading support in some of the
>>> libraries it uses. The segfault definitely violates POLA.
>>>
>>> ? Justin
>> I am conservative to not disturb the address space layout in single go.
>> If enough people test this setting, I can consider flipping the default
>> to the reverse.
>>
>> I am still curious why the things were done in this way, but nobody
>> replied.
> I suspect it was done out of reasons of being overly conservative in
> interpreting RLIMIT_STACK.  I think it is quite surprising behavior though and
> would rather we make your option the default and implement what the Open Group
> says above.
>
that is my memory..
The transition from a non threaded app to a threaded app with one 
thread is sort of an undefined area.
Feel free to change it if Dan agrees..