6

In the IDA view I see (glb_SomeVar is a byte array):

cmp al, glb_SomeVar+22h

But when I hit x to find the cross references of glb_SomeVar, I only find two other matches in the same function:

cmp al, glb_SomeVar+0Ah
cmp al, glb_SomeVar+0Bh

Is there a way to fix this, like making IDA re-analyze the selected function or even the whole code? I guess at other places, there are cross references missing too.

2 Answers 2

10

Edit -> Global -> Cross-references -> Cross reference depth. Increase as applicable.

From the documentation:

    This value "how many bytes of an object to look at to collect
    cross references". For example we have an array:
            A       db 100 dup(0)
    If some instruction refers to the 5-th element of the array:
            mov     al,A+5
     with TD=3      we'll have no xrefs displayed
     with TD=10     we'll have this xref

   IDA.CFG parameter: MAX_TAIL

"TD" here refers to "tail depth" (old name of the setting)

1
  • Ooooh didn't know this functionality. Thanks
    – k0ng0
    May 29, 2013 at 15:21
1

I think the default in IDA 6.8 is a Cross reference depth of 16. I increased this first to 32 and then to 1024 and then to 65535 (because why not). None of this led to my xref working as desired so I must not understand something.

I'm analyzing an ARM ELF shared object file. The function I'm looking at is called by a function referenced by an offset in the .init_array segment (not sure if that's relevant). The offset I want to see all references of is:

.bss:00424778 ; void *dword_424778
.bss:00424778 dword_424778    % 4

It was originally identified as unk_424778 but I pressed Y and set the type was "void *".

Hex Rays shows this assignment:

    dword_424778 = &_sF;

Using HexRaysCodeXplorer I press J to jump back to disassembly from Hex Rays. It put me on line 0026D69C:

...
.text:0026D668                 LDR             R5, [R4,R2] ; unk_424758
.text:0026D66C                 ADD             R0, R5, #0x1C
.text:0026D670                 STMIA           R5, {R3,R7}
.text:0026D674                 STR             R7, [R5,#8]
.text:0026D678                 STR             R7, [R5,#0xC]
.text:0026D67C                 STR             R7, [R5,#0x10]
.text:0026D680                 STR             R7, [R5,#0x14]
.text:0026D684                 STR             R7, [R5,#0x18]
.text:0026D688                 BL              sub_26F42C
.text:0026D68C                 LDR             R2, =(off_374A30 - 0x374C20)
.text:0026D690                 LDR             R3, [SP,#0x38+var_34]
.text:0026D694                 STR             R9, [R5]
.text:0026D698                 STR             R8, [R5,#0x24]
.text:0026D69C                 STR             R11, [R5,#0x20]
...

I don't know ARM very well but I read that the STMIA R5, {R3,R7} will result in unpredictable behavior due to the reglist ({R3,R7}) starting with a lower-number register than Rn (R5).

Could the problem be related to dword_424778 being in the .bss section?

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.