llvm dev - Nov 2013 - [LLVMdev] Android, llvm-ar and setLastModificationAndAccessTime

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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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.

Steve


On Mon, Nov 25, 2013 at 8:30 AM, James Lyon <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
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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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?

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 :-)

Cheers,
Alp.

>
> Steve
>
>
> On Mon, Nov 25, 2013 at 8:30 AM, James Lyon <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
>
>     _______________________________________________
>     LLVM Developers mailing list
>     LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>
>     http://llvm.cs.uiuc.edu
>     http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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> 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.
This is probably OK. This is just for use in llvm-ar, so it doesn't
have to be fully general. In fact, moving this function to llvm-ar
itself is probably OK too.

Cheers,
Rafael