[LLVMdev] Android, llvm-ar and setLastModificationAndAccessTime

[James Lyon]

Hmmm.... following up on your point I've noticed something strange. 
futimens is missing from the NDK (r9b; it's not in any headers and the 
libc.so files are the same all the way back to android-9), which is why 
I thought it's missing from Android generally. The NDK is by far the 
easiest way to cross-compile since it provides a standalone 
cross-compilation toolchain. It is however present in

https://android.googlesource.com/platform/prebuilts/ndk/+/master/9/platforms/android-19/arch-arm/usr/include/sys/stat.h

which seems odd to me. Steve, perhaps you know whether this is 
intentional? My googling isn't getting me anywhere on why the file I've 
linked is different to 
platforms/android-19/arch-arm/usr/include/sys/stat.h in the NDK.

James

On 25/11/13 22:12, Stephen Hines wrote:
> On Mon, Nov 25, 2013 at 12:36 PM, Alp Toker <alp at nuanti.com 
> <mailto:alp at nuanti.com>> wrote:
>
>
>     On 25/11/2013 18:27, Stephen Hines wrote:
>
>         futimens() is available in Android KitKat. We work extensively
>         with LLVM and this allowed us to remove our ugly workaround
>         for not having this functionality.
>
>
>     Hi Steve,
>
>     Is your work on a branch somewhere?
>
>
> It is all available as part of the Android Open Source Project (AOSP). 
> I should mention that we do not use the JIT path, but LLVM does 
> require futimens() to build properly for Android (hence us fixing this 
> missing part of bionic). If you want to look at local patches that we 
> have for LLVM/Clang, those are available in "external/llvm" and 
> "external/clang". We have very few differences from upstream LLVM.
>
>
>     James is putting a lot of time into this, and the LLVM community
>     has been making best efforts to help review his patches which can
>     be difficult for those who don't normally work with the Android
>     platform.
>
>     So if the work is already out there, that'd be useful to know in
>     order to avoid duplication of effort. There are lots of other
>     useful things we could be doing if support for that platform is
>     already complete somewhere on Github :-)
>
>
> http://source.android.com <http://source.android.com/> has 
> instructions for how to pull down AOSP. We don't use github.
>
> Steve
>
>
>     Cheers,
>     Alp.
>
>
>
>         Steve
>
>
>
>         On Mon, Nov 25, 2013 at 8:30 AM, James Lyon
>         <jameslyon0 at gmail.com <mailto:jameslyon0 at gmail.com>
>         <mailto:jameslyon0 at gmail.com <mailto:jameslyon0 at gmail.com>>>
>         wrote:
>
>             Hi,
>
>             I've been trying to get LLVM working as a JIT compiler on
>         Android
>             for a while. It works now, except that the
>             setLastModificationAndAccessTime function won't build
>         because the
>             Bionic C library lacks both futimes and futimens. There
>         doesn't
>             appear to be any "nice" workaround for this problem: the
>         only ways
>             I can think of to make setLastModificationAndAccessTime
>         work are
>             either to go by /proc/self/fd or invoke the system call
>         directly
>             (the second option isn't helped by the fact that the Android
>             headers don't define the relevant system call number and
>         it varies
>             between platforms).
>
>             Right now the only part of LLVM that uses this function is
>             llvm-ar, so it's not as if lack of support for this
>         function is a
>             serious shortcoming. I don't really know the history of
>             PathV1/PathV2 but I think the simplest solutions are:
>
>              1. Have setLastModificationAndAccessTime fail on platforms
>
>                 without futimes/futimens (by ENOSYS). This is pretty ugly
>                 because having a function which can never succeed
>         seems likely
>                 to confuse users.
>              2. Only declare setLastModificationAndAccessTime if it is
>
>                 actually available (add something to llvm-config.h to
>         indicate
>                 this). The downside here is that (in theory at least)
>         users
>                 need to know that setLastModificationAndAccessTime
>         might be
>                 missing, although in practise they can probably ignore
>         the issue.
>
>             (1) is trivial to implement and is what I'm doing now; I
>         can also
>             create a patch to do (2), I just thought I'd ask for
>         opinions first.
>
>             Regards,
>
>             James
>
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