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List:       gdb
Subject:    arm-elf-gdb -- finish command issue
From:       "Michael Anburaj" <embeddedeng () hotmail ! com>
Date:       2005-02-19 8:32:24
Message-ID: BAY12-F15A2569C4DF17F05E48CC4AD6F0 () phx ! gbl
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This issue is to do with arm-elf-gdb –w (insight - 5.3) not doing the 
expected thing (I may be wrong) when “finish” command is issued while the PC 
is inside a routine. It is supposed to finish the current routine & go back 
to the caller & break at the statement next to the call made to this 
function. But, it’s not happening.

Details:
--------

Setup: “arm-elf-gdb –w” invoked with the elf image build with –g option.
Target: remote serial <LPC board with remote serial gdb stubs>.
Observation: Loads fine, can see all the registers, breakpoints & single 
step works great.

Now to the problem:

Assembly dump of code portion I was debugging:

4000128a:	4843      	ldr	r0, [pc, #268]	(40001398 <.text+0x398>)
4000128c:	f950f000 	bl	40001530 <CONSOL_SendString>
40001290:	2400      	mov	r4, #0
40001292:	2101      	mov	r1, #1
40001294:	2200      	mov	r2, #0


40001530 <CONSOL_SendString>:
40001530:	b510      	push	{r4, lr}
40001532:	1c04      	mov	r4, r0		(add r4, r0, #0)
40001534:	e003      	b	4000153e <CONSOL_SendString+0xe>
40001536:	0e00      	lsr	r0, r0, #24
40001538:	3401      	add	r4, #1
4000153a:	ffe9f7ff 	bl	40001510 <CONSOL_SendCh>
4000153e:	7820      	ldrb	r0, [r4, #0]
40001540:	0600      	lsl	r0, r0, #24
40001542:	2800      	cmp	r0, #0
40001544:	d1f7      	bne	40001536 <CONSOL_SendString+0x6>
40001546:	bc10      	pop	{r4}
40001548:	bc01      	pop	{r0}
4000154a:	4700      	bx	r0

I stepped into CONSOL_SendString called from 0x4000128c. Then, while PC is 
still inside this function I issued the “finish” command. Instead of 
stopping at 0x40001290, it just continued without stopping.

GDB protocol dump (close to the problem area):

c printf "Program stopped at 0x%lx",0x40001536
c finish
w $m4000fcf0,4#f0
r +$91120040#91
w +$m40001274,2#5d
r +$10b5#f8
w +$m40001276,2#5f
r +$81b0#fb
w +$m40001274,2#5d
r +$10b5#f8
w +$M40001274,2:bebe#05
r +$OK#9a
w +$m40001290,2#5b
r +$0024#c6
w +$M40001290,2:bebe#03
r +$OK#9a
w +$c#63
r +$S05#b8
w +$g#67
r
+$911200400a00000014c000e00b0000000000000000000000000000000000000000000000000000000000 \
00000000000075120040f4fc00402115004090120040000000000000000000000000000000000000000000 \
00000000000000000000000000000000000000000000000000000000000000000000000000000000000000 \
00000000000000000000000000000000000000000000000000000000000000003300002033000060#cc w \
+$M40001274,2:10b5#6f r +$OK#9a
w +$M40001290,2:0024#3b
r +$OK#9a
w +$Hc0#db
r +$#00
w +$s#73
r +$S05#b8
w +$g#67
r
+$911200400a00000014c000e00b0000000000000000000000000000000000000000000000000000000000 \
00000000000075120040f4fc00402115004092120040000000000000000000000000000000000000000000 \
00000000000000000000000000000000000000000000000000000000000000000000000000000000000000 \
00000000000000000000000000000000000000000000000000000000000000003300006033000060#d2 w \
+$m40001274,2#5d r +$10b5#f8
w +$M40001274,2:bebe#05
r +$OK#9a
w +$m40001290,2#5b
r +$0024#c6
w +$M40001290,2:bebe#03
r +$OK#9a
w +$Hc0#db
r +$#00
w +$c#63


The follow things happen after the “finish” command was issued:
User: issues a “finish” command
GDB: sets a breakpoint at the right location, 0x40001290. The right place at 
the caller just after the function call.
GDB: issues a “continue” command
Target: breaks at 0x40001290
GDB: clears the breakpoint & issues a single step command
Target: stops at the next location, 0x40001292
GDB: sets the breakpoint back at 0x40001290 & issues a continue command


Steps 2 & 3 are the expected ones & after the target breaks at the 
0x40001290 (the right spot at the caller for the finish command), GDB should 
return to the user for further commands. Why is it doing steps 5 & 7 on its 
own?

I tried the same with mips-isa32elf-gdb. It does steps 2 & 3 only & returns 
the control to the user after 4.

Let me know the reason for this.

Thanks,
-Mike.


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