Hi,
I have the following i386 assembly code:
##########
.text
.globl _main
_main:
nop
push %ebp
mov %esp, %ebp
sub $0x4, %esp
push $msg1
call _puts
add $0x8, %esp
pop %ebp
push %ebp
sub $0x4, %esp
push $msg2
call _puts
add $0x8, %esp
mov $5, %eax
pop %ebp
ret
.data
msg1:
.ascii "Hello World!\0"
len = . - msg1
msg2:
.ascii "This is a second line.\0"
len = . - msg2
##########
Compiled under Mac OS X 10.10 with the following commands:
as -W -arch i386 -o build/test3-i386.o test3-i386.s
ld -arch i386 -macosx_version_min 10.10 -no_pie -o build/test3-i386
build/test3-i386.o -lSystem
When I run the compiled binary in the shell everything works fine,
but when I debug it from _main step-by-step with "thread step-inst-over"
in LLDB 340.99.0 (ToT) - LLDB automatically continues on the first "pop
%ebp" instruction.
:> lldb build/test3-i386
lldb:> target create "build/test3-i386"
Current executable set to 'build/test3-i386' (i386).
lldb:> br s -n main
Breakpoint 1: where = test3-i386`main, address = 0x00001f6d
lldb:> process launch
Process 66822 launched: 'build/test3-i386' (i386)
Process 66822 stopped
* thread #1: tid = 0x2af723, 0x00001f6d test3-i386`main, queue =
'com.apple.main-thread', stop reason = breakpoint 1.1
frame #0: 0x00001f6d test3-i386`main
-> 0x1f6d <test3-i386`main+0>: nop
0x1f6e <test3-i386`main+1>: pushl %ebp
0x1f6f <test3-i386`main+2>: movl %esp, %ebp
0x1f71 <test3-i386`main+4>: subl $0x4, %esp
lldb:> ni
Process 66822 stopped
* thread #1: tid = 0x2af723, 0x00001f6e test3-i386`main + 1, queue =
'com.apple.main-thread', stop reason = instruction step over
frame #0: 0x00001f6e test3-i386`main + 1
-> 0x1f6e <test3-i386`main+1>: pushl %ebp
0x1f6f <test3-i386`main+2>: movl %esp, %ebp
0x1f71 <test3-i386`main+4>: subl $0x4, %esp
0x1f74 <test3-i386`main+7>: pushl $0x200c
lldb:>
Process 66822 stopped
* thread #1: tid = 0x2af723, 0x00001f6f test3-i386`main + 2, queue =
'com.apple.main-thread', stop reason = instruction step over
frame #0: 0x00001f6f test3-i386`main + 2
-> 0x1f6f <test3-i386`main+2>: movl %esp, %ebp
0x1f71 <test3-i386`main+4>: subl $0x4, %esp
0x1f74 <test3-i386`main+7>: pushl $0x200c
0x1f79 <test3-i386`main+12>: calll 0x1f9a ; symbol stub for: puts
lldb:>
Process 66822 stopped
* thread #1: tid = 0x2af723, 0x00001f71 test3-i386`main + 4, queue =
'com.apple.main-thread', stop reason = instruction step over
frame #0: 0x00001f71 test3-i386`main + 4
-> 0x1f71 <test3-i386`main+4>: subl $0x4, %esp
0x1f74 <test3-i386`main+7>: pushl $0x200c
0x1f79 <test3-i386`main+12>: calll 0x1f9a ; symbol stub for: puts
0x1f7e <test3-i386`main+17>: addl $0x8, %esp
lldb:>
Process 66822 stopped
* thread #1: tid = 0x2af723, 0x00001f74 test3-i386`main + 7, queue =
'com.apple.main-thread', stop reason = instruction step over
frame #0: 0x00001f74 test3-i386`main + 7
-> 0x1f74 <test3-i386`main+7>: pushl $0x200c
0x1f79 <test3-i386`main+12>: calll 0x1f9a ; symbol stub for: puts
0x1f7e <test3-i386`main+17>: addl $0x8, %esp
0x1f81 <test3-i386`main+20>: popl %ebp
lldb:>
Process 66822 stopped
* thread #1: tid = 0x2af723, 0x00001f79 test3-i386`main + 12, queue =
'com.apple.main-thread', stop reason = instruction step over
frame #0: 0x00001f79 test3-i386`main + 12
-> 0x1f79 <test3-i386`main+12>: calll 0x1f9a ; symbol stub for: puts
0x1f7e <test3-i386`main+17>: addl $0x8, %esp
0x1f81 <test3-i386`main+20>: popl %ebp
0x1f82 <test3-i386`main+21>: pushl %ebp
lldb:>
Hello World!
Process 66822 stopped
* thread #1: tid = 0x2af723, 0x00001f7e test3-i386`main + 17, queue =
'com.apple.main-thread', stop reason = instruction step over
frame #0: 0x00001f7e test3-i386`main + 17
-> 0x1f7e <test3-i386`main+17>: addl $0x8, %esp
0x1f81 <test3-i386`main+20>: popl %ebp
0x1f82 <test3-i386`main+21>: pushl %ebp
0x1f83 <test3-i386`main+22>: subl $0x4, %esp
lldb:>
Process 66822 stopped
* thread #1: tid = 0x2af723, 0x00001f81 test3-i386`main + 20, queue =
'com.apple.main-thread', stop reason = instruction step over
frame #0: 0x00001f81 test3-i386`main + 20
-> 0x1f81 <test3-i386`main+20>: popl %ebp
0x1f82 <test3-i386`main+21>: pushl %ebp
0x1f83 <test3-i386`main+22>: subl $0x4, %esp
0x1f86 <test3-i386`main+25>: pushl $0x2019
lldb:>
This is a second line.
Process 66822 exited with status = 5 (0x00000005)
lldb:> ^D
When I remove
pop %ebp
push %ebp
it works fine. Then LLDB stops after each single instruction step over
until to the end of the program.
When I also remove the instructions for the output of the second puts()
it continues at the bottom "pop %ebp", before "ret":
##########
.text
.globl _main
_main:
nop
push %ebp
mov %esp, %ebp
sub $0x4, %esp
push $msg1
call _puts
add $0x8, %esp
mov $5, %eax
pop %ebp
ret
.data
msg1:
.ascii "Hello World!\0"
len = . - msg1
msg2:
.ascii "This is a second line.\0"
len = . - msg2
##########
It should do only one instruction step over.
What am I doing wrong?
Br,
Christian
--
Christian Mayer
software developer
http://fox21.at
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