Discussion:
How step over a ass call command?
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Yao Qi
2014-10-07 14:19:05 UTC
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Suppose that I use gdb with a binary file with source stripped.
What do you mean by "a binary file with source stripped"? Did you
compile without debug information? My gdb (built from current git repo
for x86-linux target) works correctly for binary without debug info.

(gdb) disassemble
Dump of assembler code for function main:
0x08048406 <+0>: push %ebp
0x08048407 <+1>: mov %esp,%ebp
=> 0x08048409 <+3>: call 0x8048400 <foo>
0x0804840e <+8>: mov $0x0,%eax
0x08048413 <+13>: pop %ebp
0x08048414 <+14>: ret
End of assembler dump.
(gdb) ni
0x0804840e in main ()
Try nexti, which is defined as
Execute one machine instruction, but if it is a function call, proceed
until the function returns
I am sorry. I meant to say "nexti" in my original email. "nexti" seems
to the same as "stepi" when the source code is stripped. Is it
supposed to be so?
No, it looks a bug to me. What is your gdb version? or you can report
this bug here https://sourceware.org/bugzilla/
--
Yao (齐尧)
Pedro Alves
2014-10-07 16:24:15 UTC
Permalink
Post by Yao Qi
Suppose that I use gdb with a binary file with source stripped.
What do you mean by "a binary file with source stripped"? Did you
compile without debug information? My gdb (built from current git repo
for x86-linux target) works correctly for binary without debug info.
(gdb) disassemble
0x08048406 <+0>: push %ebp
0x08048407 <+1>: mov %esp,%ebp
=> 0x08048409 <+3>: call 0x8048400 <foo>
0x0804840e <+8>: mov $0x0,%eax
0x08048413 <+13>: pop %ebp
0x08048414 <+14>: ret
End of assembler dump.
(gdb) ni
0x0804840e in main ()
Try nexti, which is defined as
Execute one machine instruction, but if it is a function call, proceed
until the function returns
I am sorry. I meant to say "nexti" in my original email. "nexti" seems
to the same as "stepi" when the source code is stripped. Is it
supposed to be so?
No, it looks a bug to me. What is your gdb version? or you can report
this bug here https://sourceware.org/bugzilla/
0x1ea7 <main+45>: mov %eax,(%esp)
0x1eaa <main+48>: call 0x1f14
0x1eaf <main+53>: mov 0x1180(%ebx),%ecx

Doesn't look like GDB which function is at 0x1f14.

"nexti" relies on being able to backtrace out of that "function",
and check that the previous caller is still found at frame #1, to
detect that a function call was done. So run to that "call" line,
and then do "bt". And then do "stepi" to step that instruction
instead of "nexti", and then do "bt" again. If the second
backtrace doesn't have one extra frame, or if the frame that was frame
#0 in the first backtrace is frame #1 in the second backtrace,
then "nexti" won't work either.

Thanks,
Pedro Alves
Pedro Alves
2014-10-07 16:26:47 UTC
Permalink
Post by Pedro Alves
"nexti" relies on being able to backtrace out of that "function",
and check that the previous caller is still found at frame #1, to
detect that a function call was done. So run to that "call" line,
and then do "bt". And then do "stepi" to step that instruction
instead of "nexti", and then do "bt" again. If the second
backtrace doesn't have one extra frame, or if the frame that was frame
#0 in the first backtrace is frame #1 in the second backtrace,
^NOT^
Post by Pedro Alves
then "nexti" won't work either.
Thanks,
Pedro Alves

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