[LLVMdev] Customize Standard C Library Using LLVM (to support llvm backend optimization)

[Kostya Serebryany]

On Wed, Mar 11, 2015 at 9:55 AM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Wed, Mar 11, 2015 at 9:13 AM, Chao Yan <yanchao2012 at gmail.com> wrote:
>
>> Purpose:
>>
>> I implemented a pass on LLVM backend that changes the output format of
>> *ARM* assembly/binary (e.g add a jump at the end of each basic block to
>> eliminate fall through). By calling:
>>
>> llc -march=arm somefile.bc
>>
>> it generates expected arm assembly/binary that runs properly on arm gnu
>> linux (I use qemu-arm and gem5 to simulate it). Now I want to do the same
>> thing on standard c library, but here are problems.
>> Problems:
>>
>> According to:
>>
>> http://article.gmane.org/gmane.comp.compilers.llvm.devel/77025 https://llvm.org/svn/llvm-project/llvm/tags/RELEASE_14/docs/OpenProjects.html#glibc
>>
>> compiling glibc using llvm may not be a proper option.
>>
> Not an option /yet/, but it's a work in progress, by the sounds of it.
> Kostya's been working on it recently & it sounds like there's one or two
> things in the source code to tackle, then some build issues?
>

I've been successfully building glibc's libc.so with clang (and asan!) for
the past two weeks,
but the process is manual and still requires a few patches and ugly hacks.
https://sourceware.org/glibc/wiki/GlibcMeetsClang


>
>
>> On the other hand, according to:
>>
>> http://lists.cs.uiuc.edu/pipermail/llvmdev/2012-January/047088.html
>>
>> llvm could be able to compile newlib, thus people consider newlib as an
>> alternative. However, according to:
>>
>> http://www.embecosm.com/appnotes/ean9/ean9-howto-newlib-1.0.html#id2711887
>>
>> newlib intends to support binaries for bare metal (no OS) software. It
>> implements only the hardware independent parts (e.g libc and libm) and
>> leave a stub for each hardware dependent syscall (e.g everything in
>> libgloss).
>>
>> In fact I tried to compile a simple "hello world" c program using
>> arm-none-eabi-gcc which was configured with "--with-newlib" option, the
>> program execution ends up with segmentation faults on both qemu-arm and
>> gem5.
>> Questions:
>>
>> I'm not sure if the newlib is compatible with glibc. I'm wondering if I
>> could use llvm to cross-compile the machine independent parts (at the same
>> time change the arm output format) from newlib and use
>> arm-none-linux-gnueabi-gcc to cross-compile the machine dependent parts
>> from glibc and put these two parts together to generate my own standard c
>> library?
>>
>> There might be mistakes/misunderstandings in my work. Are there any other
>> possible methods that could add my changes to at least part of the standard
>> c libraries, and make the program run on qemu-arm or gem5?
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150311/7a432095/attachment.html>