[Haskell-iPhone] help for ghc android cross compiler

[Stephen Blackheath [to GHC-iPhone]]

Nathan,

My GHC-iOS is based on HEAD from about November 2012.

The register that's used for base is defined in includes/stg/MachRegs.h 
and is meant to be r4. This has never changed since the ARM work was 
done. This is likely to be new breakage.

One possibility: There are certain versions of llvm that break with GHC 
and ARM. llvm-3.0 is known to work. I believe this has been fixed since 
(so new llvm-version should work), but I haven't confirmed it.

Looking at the cmm source for stg_returnToStackTop, the use of r0 looks 
wrong because the comment says it's not using C arguments. r0-r3 are not 
callee-saves and r0 is normally a C call argument and return value.

I just did a compile for Emdebian Linux (but haven't run any generated 
code yet), and I'm getting almost the same as you:

00000000 <stg_returnToStackTop>:
    0:   e92d4010        push    {r4, lr}
    4:   e24dd010        sub     sp, sp, #16
    8:   e590108c        ldr     r1, [r0, #140]  ; 0x8c
    c:   e3a04000        mov     r4, #0
   10:   e591200c        ldr     r2, [r1, #12]
   14:   e592100c        ldr     r1, [r2, #12]
   18:   e580409c        str     r4, [r0, #156]  ; 0x9c
   1c:   e2822064        add     r2, r2, #100    ; 0x64
   20:   e5904094        ldr     r4, [r0, #148]  ; 0x94
   24:   e594c004        ldr     ip, [r4, #4]
   28:   e594e000        ldr     lr, [r4]
   2c:   e594401c        ldr     r4, [r4, #28]
   30:   e08e4604        add     r4, lr, r4, lsl #12
   34:   e2444001        sub     r4, r4, #1
   38:   e5804084        str     r4, [r0, #132]  ; 0x84
   3c:   e5914000        ldr     r4, [r1]
   40:   e58d200c        str     r2, [sp, #12]
   44:   e24c2004        sub     r2, ip, #4
   48:   e1a0e00f        mov     lr, pc
   4c:   e1a0f004        mov     pc, r4
   50:   e28dd010        add     sp, sp, #16
   54:   e8bd4010        pop     {r4, lr}
   58:   e1a0f00e        mov     pc, lr

On the iPhone I get this:

_stg_returnToStackTop:
00000000        e5946064        ldr     r6, [r4, #100]
00000004        e3a03000        mov     r3, #0  @ 0x0
00000008        e596600c        ldr     r6, [r6, #12]
0000000c        e596500c        ldr     r5, [r6, #12]
00000010        e5843074        str     r3, [r4, #116]
00000014        e286b064        add     fp, r6, #100    @ 0x64
00000018        e594306c        ldr     r3, [r4, #108]
0000001c        e1c300d0        ldrd    r0, [r3]
00000020        e593301c        ldr     r3, [r3, #28]
00000024        e0803603        add     r3, r0, r3, lsl #12
00000028        e2416004        sub     r6, r1, #4      @ 0x4
0000002c        e2433001        sub     r3, r3, #1      @ 0x1
00000030        e584305c        str     r3, [r4, #92]
00000034        e5953000        ldr     r3, [r5]
00000038        e12fff33        blx     r3
0000003c        e12fff1e        bx      lr

A comparison strongly supports your idea that it's using r0 when it 
should be using r4.

I am going to try some different versions of llvm.


Steve

On 16/01/13 06:59, Nathan Hüsken wrote:
> Hey,
>
> I am currently trying to get a ghc cross compiler for android linux to work.
> I am basing this on the development version (HEAD). I succeeded building
> the compiler. Unfortunately, the executables produced by the compiler
> segfault on my android device.
>
> If I do an unregisterised build, it works!
>
> Since the iphone is also an arm platform, I was hoping someone here
> could help me a little bit.
>
> I investigate the problem a little bit (see this thread:
> http://www.haskell.org/pipermail/ghc-devs/2013-January/000013.html) and
> I am guessing (I am no expert) that it is an arm problem, not android.
>
> It seems like the wrong register is used for base (r0 instead of r4).
>
> * On which ghc version is the iphone fork based?
> * Are there any arm fixes in the iphone fork that could be related to this?
>
> Thank you!
> Nathan
>
>
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