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Message-ID: <20170624221848.GW1627@brightrain.aerifal.cx>
Date: Sat, 24 Jun 2017 18:18:48 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: pthread_getattr_np doing loads of mremaps on ARM, MIPS
under QEMU user-mode
On Sun, Jun 25, 2017 at 01:05:52AM +0300, Tobias Koch wrote:
> Hi,
>
> thank you! And yes, you are absolutely right. QEMU always fails in
> mmap.c after looking at page flags in the extended memory range:
>
> int prot = 0;
> if (reserved_va && old_size < new_size) {
> abi_ulong addr;
> for (addr = old_addr + old_size;
> addr < old_addr + new_size;
> addr++) {
> prot |= page_get_flags(addr);
> }
> }
> if (prot == 0) {
> host_addr = mremap(g2h(old_addr), old_size, new_size, flags);
> if (host_addr != MAP_FAILED && reserved_va && old_size > new_size) {
> mmap_reserve(old_addr + old_size, new_size - old_size);
> }
> } else {
> /* musl's pthread_getattr_np always fails here doing mremaps: */
> errno = ENOMEM;
> host_addr = MAP_FAILED;
> }
>
> I wonder why it cannot just try the remap directly and use the
> result of that, but that's clearly a question for the QEMU people.
They can't try to mremap arbitrary addresses in the emulated address
space without first translating them to the host address space. When
page_get_flags fails they probably need to be generating EFAULT
themselves or something.
Rich
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