RTS: mmap fails on RISC-V with Linux 6.8

[Andreas Klebinger]

There have been changes to upstream that likely fixes this.

See https://gitlab.haskell.org/ghc/ghc/-/issues/25492

If you can reproduce this issue using a ghc build base of a recent ghc 
master version please let us know!

Cheers

On 27/05/2025 20:35, Heinrich Schuchardt via ghc-devs wrote:

> The following bug related to the Haskell runtime was reported in 
> Launchpad:
>
> Haskell's default behaviour of using large-address-space is causing 
> pandoc to stuck in an infinite loop on QEMU 10 Edit
> https://bugs.launchpad.net/ubuntu/+source/ghc/+bug/2111581
>
> The problem seems to relate to the following loop in 
> osReserveHeapMemory():
>
> https://gitlab.haskell.org/ghc/ghc/-/blob/master/rts/posix/OSMem.c?ref_type=heads#L589 
>
>
> According to the mmap() manpage the address passed to the kernel in 
> only a hint there is no guarantee that the same address will be used 
> for allocation.
>
> As shown in the strace logs attached in Launchpad this code can lead 
> to an endless loop when the kernel decides always to return an address 
> below 8 GiB.
>
> It might make sense to round up the address to 8 GiB if the returned 
> address is below 8 GiB and reduce *len accordingly instead of retrying.
>
> Best regards
>
> Heinrich
>
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