musl - pthread_getattr_np doing loads of mremaps on ARM, MIPS under QEMU user-mode

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Message-ID: <a3a76ce8-0968-7c00-d54c-f68f1ad526b1@nonterra.com>
Date: Thu, 15 Jun 2017 16:08:03 +0300
From: Tobias Koch <tobias.koch@...terra.com>
To: musl@...ts.openwall.com
Subject: pthread_getattr_np doing loads of mremaps on ARM, MIPS under QEMU
 user-mode

Hi,

running under QEMU user mode, Ruby 2.4 (and it seems also Guile) ARM and 
MIPS binaries take a long time to start and eventually crash. The long 
startup seems to come from this loop

   while (mremap(p-l-PAGE_SIZE, PAGE_SIZE, 2*PAGE_SIZE, 0)==MAP_FAILED 
&& errno==ENOMEM)
           l += PAGE_SIZE;

being executed hundreds of times in pthread_getattr_np. Any idea what 
this could be about except from maybe being a QEMU bug?

The subsequent crash then occurs after memory set aside by alloca is 
accessed. I think this may be unrelated.

Tobias

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