Support xc16 (pic) disassembler output

[sarfata]

The disassembly generated by the xc16 toolchain (microchip) generates symbols for every label in the source code. For example, this is one function that gets transformed into multiple symbols: SetUsbChannel, .L3, .L4, .L6, .L2.

00007270 <_SetUsbChannel>:
SetUsbChannel():
/project/bootload.X/usb_switch.c:21
    7270:	88 1f 78    	mov.w     w8, [w15++]
    7272:	00 04 78    	mov.w     w0, w8
/project/bootload.X/usb_switch.c:25
    7274:	e1 0f 54    	sub.w     w8, #0x1, [w15]
    7276:	09 00 32    	bra       Z, 0x728a <.L4>
    7278:	03 00 39    	bra       NC, 0x7280 <.L3>
    727a:	e2 0f 54    	sub.w     w8, #0x2, [w15]
    727c:	0f 00 3a    	bra       NZ, 0x729c <.L2>
    727e:	0a 00 37    	bra       0x7294 <.L6>

00007280 <.L3>:
/project/bootload.X/usb_switch.c:28
    7280:	e0 00 20    	mov.w     #0xe, w0
    7282:	a0 ff 07    	rcall     0x71c4 <_output_high> <.LFB8> <.LFE7>
/project/bootload.X/usb_switch.c:29
    7284:	f0 00 20    	mov.w     #0xf, w0
    7286:	a8 ff 07    	rcall     0x71d8 <_output_low> <.LFB9> <.LFE8>
/project/bootload.X/usb_switch.c:30
    7288:	09 00 37    	bra       0x729c <.L2>

0000728a <.L4>:
/project/bootload.X/usb_switch.c:33
    728a:	e0 00 20    	mov.w     #0xe, w0
    728c:	a5 ff 07    	rcall     0x71d8 <_output_low> <.LFB9> <.LFE8>
/project/bootload.X/usb_switch.c:34
    728e:	f0 00 20    	mov.w     #0xf, w0
    7290:	a3 ff 07    	rcall     0x71d8 <_output_low> <.LFB9> <.LFE8>
/project/bootload.X/usb_switch.c:35
    7292:	04 00 37    	bra       0x729c <.L2>

00007294 <.L6>:
/project/bootload.X/usb_switch.c:38
    7294:	e0 00 20    	mov.w     #0xe, w0
    7296:	a0 ff 07    	rcall     0x71d8 <_output_low> <.LFB9> <.LFE8>
/project/bootload.X/usb_switch.c:39
    7298:	f0 00 20    	mov.w     #0xf, w0
    729a:	94 ff 07    	rcall     0x71c4 <_output_high> <.LFB8> <.LFE7>

0000729c <.L2>:
/project/bootload.X/usb_switch.c:43
    729c:	78 43 88    	mov.w     w8, 0x86e
/project/bootload.X/usb_switch.c:44
    729e:	4f 04 78    	mov.w     [--w15], w8
    72a0:	00 00 06    	return

The current result is that for a elf file disassembled with this toolset, 80% of the code size goes in <unknown>/<unknown> and looking at SetUsbChannel only shows the first few lines of the assembly. Callers/Callees counting is also broken (related to #7/#8/#20 probably).

Todo:

• [ ] add some tests parsing this type of output
• [ ] parse assembly all the way til the end of the function (until beginning of the next one is probably the only way to detect the end of one)
• [ ] figure out a way to sum the size of all the symbols that make one function