[LLVMdev] Disassembly broken for thumb LDR

[Vladimir Pouzanov]

Hi all.

I'm investigating an issue with incorrect lldb's disassembly output. I have two bytes in question: 4e5f

lldb (via the llvm's LLVMARMCodeGen) is providing the following mnemonics:

ldr    r6, #380,

However the value for ldr is "an 8-bit value that is multiplied by 4 and added to the value of the PC to form the memory address" (via ARMARM), so that the correct mnemonics is:

ldr     r6, [pc, #380]

(provided by Apple's otool).

I've traced the issue down to ARMInstrThumb.td:

// A8.6.57 & A8.6.60
defm tLDR  : thumb_ld_rr_ri_enc<0b100, 0b0110, t_addrmode_rrs4,
                                t_addrmode_is4, AddrModeT1_4,
                                IIC_iLoad_r, IIC_iLoad_i, "ldr",
                                UnOpFrag<(load node:$Src)>>;

In the generated TableGen output the issue lies around line 4992:

4992	    case ARM::tUXTH: printOperand(MI, 1, O); break;

As the operand is not enough in this case.

I'm pretty stuck at the TableGen deciphering to fix the issue. It'll be nice if someone with more llvm skills would check the file and make the required fix.

-- 
Vladimir Pouzanov
http://www.farcaller.net/


-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 4454 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20120326/02e45133/attachment.bin>