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Re: mmap64 with very large offset broken since glibc 2.26 (MIPS64 n32)
- From: Florian Weimer <fweimer at redhat dot com>
- To: Thomas De Schampheleire <patrickdepinguin at gmail dot com>
- Cc: libc-alpha at sourceware dot org, Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- Date: Thu, 13 Jun 2019 13:58:39 +0200
- Subject: Re: mmap64 with very large offset broken since glibc 2.26 (MIPS64 n32)
- References: <CAAXf6LWW9kknauk11d2Yi-18f6sB1rAGcfhnW+=eKDK8jDBVNA@mail.gmail.com>
* Thomas De Schampheleire:
> Hello,
>
> In glibc 2.26, a change was made to the behavior of mmap64, as a fix
> for bug 21270 (mmap64 silently truncates large offset values) [1], via
> commit 158d5fa0e1906e7810bdc6ecb7bf598dcc3cd17d.
> Practically, with the new behavior, doing mmap64 with an offset larger
> than 1<<44 now fails with errno=EINVAL. The reasoning in this bug is
> that offsets greater than 1<<44 are silently truncated, and so better
> to fail early.
>
> However, I have several cases in embedded applications where such
> mmap64 with large offset values is performed, and it worked correctly
> (< 2.26). In these applications, a physical memory region is mapped
> into the virtual address space, by performing an mmap64 on /dev/mem.
> The offset is very large because this is accessing devices high up in
> the memory range.
Is the bug here that mmap64 is not used with a 64-bit argument? Should
this system call have a long long argument?
Thanks,
Florian