Incorrect function size inside ARM ELF object

Question

readelf output of the object file:

Symbol table \'.symtab\' contains 15 entries:
   Num:    Value  Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 N         


        

Answer 1

Technically, your "missing byte" is the one right there at 0x0.

Note that you're looking at the value of the symbol, i.e. the runtime function address (this would be a lot clearer if your .text section VMA wasn't 0). Since they're Thumb functions, the addresses have bit 0 set such that the processor will switch to Thumb mode when calling them; the actual locations of those instructions are still halfword-aligned, i.e. 0x0, 0xc4, 0x114, etc. since they couldn't be executed otherwise (you'd take a fault for a misaligned PC). Strip off bit 0 as per what the ARM ELF spec says about STT_FUNC symbols to get the actual VMA of the instruction corresponding to that symbol, then subtract the start of the section and you should have the same relative offset as within the object file itself.

 = ( & ~1) - 

The extra halfword padding after some functions just ensures each symbol is word-aligned - there are probably various reasons for this, but the first one that comes to mind is that the adr instruction wouldn't work properly if they weren't.