[llvm-commits] Commit 141135 breaks thumb assembly

[Owen Anderson]

James,

This will actually be somewhat hard to implement (or at least will require adding knowledge of Thumb to target-independent bits).  I think I'll disable mapping symbols on ELF targets.  On MachO, we don't have different mapping symbols for ARM/Thumb modes.

--Owen

On Oct 14, 2011, at 1:59 AM, James Molloy wrote:

> Hi Owen,
> 
> Your commit 141135 causes incorrect assembly to be output in Thumb mode. You modified MCAsmStreamer to emit mapping symbols at the beginning of code and data sections ('$a.0', '$d.0'). In thumb mode, it will also output an '$a' which is incorrect, as $a says that the following code is ARM-mode.
> 
> After assembly with GNU As, the correct '$t' mapping symbol is added by the assembler, which causes both a $a and a $t to be at the same address and confuses our linker (and would confuse most linkers and disassembly tools!):
> 
> .LBB0_2:                                @ %switch.case.1
> $a.0:
>        movw    r0, :lower16:Int_Glob
>        movt    r0, :upper16:Int_Glob
>        ldr     r0, [r0]
>        cmp     r0, #101
>        blt     .LBB0_4
> 
> Assembles to:
> 
>    $a
>    $t
>        0x00000018:    f2400000    @...    MOVW     r0,#:LOWER16: Int_Glob
>        0x0000001c:    f2c00000    ....    MOVT     r0,#:UPPER16: Int_Glob
>        0x00000020:    6800        .h      LDR      r0,[r0,#0]
>        0x00000022:    2865        e(      CMP      r0,#0x65
>        0x00000024:    db01        ..      BLT      {pc}+0x6 ; 0x2a
> 
> This is incorrect by the ABI - the mapping symbols contradict.
> 
> Could you please fix this?
> 
> Cheers,
> 
> James
> 
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