Re: [Tinycc-devel] arm64: Fix crash due to incorrect page alignment on centos

[Michael Matz]

Hi,

On Wed, 4 Sep 2019, Christian Jullien wrote:

> Ok but what happens if s.o. configures its system with HUGE PAGE support?

That doesn't affect the user visible page size (i.e. the mmap granularity 
will still be 4 or 64 KB), ELF files won't be mapped into huge pages 
(except perhaps transparently by the kernel in which case the user won't 
notice either).  And yes, Edmund is right, this is about how the ELF files 
are generated, that's not configurable at runtime.

Normally, for accessing huge pages you either need a helper library or use 
special flags for mmap (in which case it's again at the kernels discretion 
to really use huge pages).


Ciao,
Michael.

> https://wiki.debian.org/Hugepages
> 
> See for example 
> https://stackoverflow.com/questions/21159982/how-to-get-the-page-size-of-a-specific-address-programmatically
> 
> C.
> 
> -----Original Message-----
> From: Tinycc-devel [mailto:tinycc-devel-bounces+eligis=address@hidden] On 
> Behalf Of Edmund Grimley Evans
> Sent: Wednesday, September 04, 2019 09:55
> To: address@hidden
> Subject: Re: [Tinycc-devel] arm64: Fix crash due to incorrect page alignment 
> on centos
> 
> Christian Jullien <address@hidden>:
> 
> > I have to questions with your patch:
> > - Why then my FC30 aarch64 PRi port does not fail, I'm running tcc for 
> > several months on it. Maybe I'm luck?
> > - pagesize can be configured by sys admin (including huge pages up to 1GB) 
> > , so IMHO, the right patch is to use the POSIX portable value of  
> > sysconf(_SC_PAGESIZE) you can compute once and put in a variable when tcc 
> > initializes.
> 
> The user-visible page size is 4K, 16K or 64K (according to
> https://wiki.debian.org/ArchitectureSpecificsMemo, which has similar
> information for a lot of different architectures).
> 
> I think we're talking about generating an object file here, which
> might be used on a different system, so we have to assume the largest
> size.
> 
> Edmund
> 
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