ARCv2: objdump incorrectly disassembling jump tables as random instructions (including floating point)

[vineetgarc]

An ARCv2 binary was incorrectly flagged as having hw float instructions despit ethe soft-float build. Turns out that objdump can incorrectly disassemble random fragments of jump tables - embedded inline on .text.

ARCv2 codegen

	sub r0,r0,129	# tmp316, param,
	brhi r0, 7, @.L204	#, tmp316,,
	ldb.x	r0,[@.L209,r0]	# tmp317,, tmp316
	add_s r0,r0,@.L209	# tmp317, tmp317,
	j_s [r0]	# tmp317
.L209:
	.byte .L213-.L209
	.byte .L212-.L209
	.byte .L211-.L209
	.byte .L211-.L209
	.byte .L204-.L209
	.byte .L204-.L209
	.byte .L210-.L209
	.byte .L208-.L209
	.align 2

ARCv2 objdump rendering of final executable (NOK)

   5d29a:	2082 0042           	sub	r0,r0,129
   5d29e:	08eb 8215           	brhs.nt	r0,0x8,-22	;5d286 <stty_main+0x2ce>
   5d2a2:	2633 7000 0005 d2b2 	ldb.x	r0,[0x5d2b2,r0]
   5d2aa:	70c3 0005 d2b2      	add_s	r0,r0,0x5d2b2
   5d2b0:	7800                	j_s	[r0]
   5d2b2:	3608 1818           	fcvt32	r24,r14,r32
                                        ^^^^^^^^
   5d2b6:	d4d4                	ld_s	r12,[pcl,0x350]	;5d604 <tail_main+0x2b0>
   5d2b8:	5e50                	ei_s	0x250

ARMv7 codegen

	sub	r0, r0, #129	@ tmp287, param,
	cmp	r0, #7	@ tmp287,
	ldrls	pc, [pc, r0, asl #2]	@ tmp287
	b	.L228	@
.L233:
	.word	.L237
	.word	.L236
	.word	.L235
	.word	.L235
	.word	.L228
	.word	.L228
	.word	.L234
	.word	.L232
.L237:

ARMv7 objdump

   bccb8:	e2400081 	sub	r0, r0, #129	; 0x81
   bccbc:	e3500007 	cmp	r0, #7
   bccc0:	979ff100 	ldrls	pc, [pc, r0, lsl #2]
   bccc4:	eafffff2 	b	bcc94 <stty_main+0x474>
   bccc8:	000bcce8 	.word	0x000bcce8
   bcccc:	000bcd24 	.word	0x000bcd24
   bccd0:	000bccfc 	.word	0x000bccfc
   bccd4:	000bccfc 	.word	0x000bccfc
   bccd8:	000bcc94 	.word	0x000bcc94
   bccdc:	000bcc94 	.word	0x000bcc94
   bcce0:	000bcd48 	.word	0x000bcd48
   bcce4:	000bcd60 	.word	0x000bcd60
   bcce8:	e1a01009 	mov	r1, r9

ARMv8 apparently generates a seperate .rodata section

[vineetgarc]

issue-385.tar.gz

[claziss]

Arm is using special symbols to mark if a frag is data, arm code or thumb see chapter 4.5.5 of AAELF. The disassembler is recognizes these special symbols and it takes the appropriate action as indicated. These special symbols are added by the assembler.

[Lorimuenchen]

@claziss I just start learning objdump flow for a ArcV2 bin, could you kindly share your command, thanks

[Lorimuenchen]

issue-385.tar.gz

could you kindly share your command, I want to do objdump flow for ArcV2, but the tool recognize instruction bin to data file ...