From Newsgroup: comp.lang.asm.x86

All,
It has been 30+ years since I played around with some assembly.
Just for learning purposes I'm doing some more playing :-)

First some information :
The system I'm on:
[martijn@fedora asm]$ uname -a
Linux fedora 6.2.15-100.fc36.x86_64 #1 SMP PREEMPT_DYNAMIC Thu May 11 16:51:53 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
[martijn@fedora asm]$

Then for completeness also the program (for this particular problem I do not think it's that relevant :-) ):
[martijn@fedora asm]$ cat een.asm
section .data

section .text

global _start

_start:
mov al, 1 ; mov 1 into the al register
add al, 1 ; add one to the al register

mov rax, 60 ; syscall for exit
mov rdi, 0 ; Return code
syscall
[martijn@fedora asm]$


Then I compile, link and run the progrm:
[martijn@fedora asm]$ nasm -f elf64 -gdwarf een.asm
[martijn@fedora asm]$ ld -m elf_x86_64 -o een een.o
[martijn@fedora asm]$ ./een
[martijn@fedora asm]$

So far so good (I think):

But I want to see what is actually happening, so I want to see it in my debugger :

[martijn@fedora asm]$ gdb een
GNU gdb (GDB) Fedora 12.1-2.fc36
....
....
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from een...
(gdb) list
1 section .data
2
3 section .text
4
5 global _start
6
7 _start:
8 mov al, 1 ; mov 1 into the al register
9
10 add al, 1 ; add one to the al register
(gdb) break 8
No line 8 in the current file.
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb)


As you can see I can not set a breakpoint. And that's my problem.
Whitout breakpoints I can not step through my program.

Does anyone have any pointers/tips/trics on how to resolve this issue.

(I know myself...I probably oversee the obvious...do not hesitate to point that out)

Best Regards,
Martijn Bos

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From Newsgroup: comp.lang.asm.x86

On 2023-11-30, Martijn Bos wrote:

Does anyone have any pointers/tips/trics on how to resolve this issue.

(I know myself...I probably oversee the obvious...do not hesitate to point that out)

I would just use the disassembler, for example `x/10i _start` instead of
`list _start`!

I don't think nasm will generate line info automatically (just names),
so you would set breakpoints on symbols `b _start` or addresses `b
*0x401000)

However... gas can do it if you prefer this style. Your code is
basically valid gas syntax already. Just add `.intel_syntax noprefix`
and add a `.` before directives, e.g. .section, .global, etc, and use #
for comments instead of ;.

Then you can use `as -g foo.asm -o foo.o` instead.

Now `b foo.asm:123` should work.

Nasm and gas are both great assemblers, it doesn't make much difference
which one you choose while you're getting started.

Tavis.
--
_o) $ lynx lock.cmpxchg8b.com
/\\ _o) _o) $ finger taviso@sdf.org
_\_V _( ) _( ) @taviso

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From Newsgroup: comp.lang.asm.x86

On 2023-12-02, Tavis Ormandy <taviso@nospicedham.gmail.com> wrote:

On 2023-11-30, Martijn Bos wrote:

Does anyone have any pointers/tips/trics on how to resolve this issue.

(I know myself...I probably oversee the obvious...do not hesitate to point that out)

I would just use the disassembler, for example `x/10i _start` instead of `list _start`!

I don't think nasm will generate line info automatically (just names),
so you would set breakpoints on symbols `b _start` or addresses `b
*0x401000)

However... gas can do it if you prefer this style. Your code is
basically valid gas syntax already. Just add `.intel_syntax noprefix`
and add a `.` before directives, e.g. .section, .global, etc, and use #
for comments instead of ;.

Then you can use `as -g foo.asm -o foo.o` instead.

Now `b foo.asm:123` should work.

Nasm and gas are both great assemblers, it doesn't make much difference
which one you choose while you're getting started.

Tavis.

NASM can generate debugging information which I believe will generate
line info. Pass '-F dwarf' option to nasm if under Linux, and you should see each
line of source in the debugger.

ie.
nasm -f elf32 -F dwarf hello.asm


P.S., I assume you're the same Tavis who is known for your FVWM
config?

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From Newsgroup: comp.lang.asm.x86

Thank you so much for this information.

Today I have to visit my parents (my father turned 83 :-))
So...no testing today.

I'll report back hopefully tomorrow.

Best Regards,
Martijn

Op zaterdag 2 december 2023 om 01:36:03 UTC+1 schreef Tavis Ormandy:

On 2023-11-30, Martijn Bos wrote:

Does anyone have any pointers/tips/trics on how to resolve this issue.

(I know myself...I probably oversee the obvious...do not hesitate to point that out)

I would just use the disassembler, for example `x/10i _start` instead of `list _start`!

I don't think nasm will generate line info automatically (just names),
so you would set breakpoints on symbols `b _start` or addresses `b *0x401000)

However... gas can do it if you prefer this style. Your code is
basically valid gas syntax already. Just add `.intel_syntax noprefix`
and add a `.` before directives, e.g. .section, .global, etc, and use #
for comments instead of ;.

Then you can use `as -g foo.asm -o foo.o` instead.

Now `b foo.asm:123` should work.

Nasm and gas are both great assemblers, it doesn't make much difference which one you choose while you're getting started.

Tavis.

--
_o) $ lynx lock.cmpxchg8b.com
/\\ _o) _o) $ finger tav...@sdf.org
_\_V _( ) _( ) @taviso

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From Newsgroup: comp.lang.asm.x86

Hi,

Thanks for taking the tmie to answer.
See my remarks inline

Best regards,
Martijn

Op zaterdag 2 december 2023 om 10:24:46 UTC+1 schreef Borax Man:

On 2023-12-02, Tavis Ormandy <tav...@nospicedham.gmail.com> wrote:

On 2023-11-30, Martijn Bos wrote:

Does anyone have any pointers/tips/trics on how to resolve this issue.

(I know myself...I probably oversee the obvious...do not hesitate to point that out)

I would just use the disassembler, for example `x/10i _start` instead of `list _start`!

I don't think nasm will generate line info automatically (just names),
so you would set breakpoints on symbols `b _start` or addresses `b *0x401000)

However... gas can do it if you prefer this style. Your code is
basically valid gas syntax already. Just add `.intel_syntax noprefix`
and add a `.` before directives, e.g. .section, .global, etc, and use # for comments instead of ;.

Then you can use `as -g foo.asm -o foo.o` instead.

Now `b foo.asm:123` should work.

Nasm and gas are both great assemblers, it doesn't make much difference which one you choose while you're getting started.

Tavis.

NASM can generate debugging information which I believe will generate
line info. Pass '-F dwarf' option to nasm if under Linux, and you should see each
line of source in the debugger.

ie.
nasm -f elf32 -F dwarf hello.asm

From 'man nasm' I quote:
==quote==
-F format
Specifies the debug information format. To see a list of valid output formats, use the -y option (for example -felf -y).

-g
Causes nasm to generate debug information.

-gformat
Equivalent to -g -F format.>
==unquote==

When I tried your suggestion I got the same result:
(gdb) break 8
No line 8 in the current file.

So i tried -gdwarf

Same result.

Maybe I should also give the linker some options to handle debug information (?)


Anyway....I'm off for familiy matters.

I'll try further tomorrow

P.S., I assume you're the same Tavis who is known for your FVWM
config?

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From Newsgroup: comp.lang.asm.x86

On 2023-12-02, Borax Man wrote:

NASM can generate debugging information which I believe will generate
line info. Pass '-F dwarf' option to nasm if under Linux, and you should see each
line of source in the debugger.

You're thinking of line markers I think (like %line 123), but I think
Martijn wants the assembler to do that automatically so that b
foo.asm:123 works, like it does in gas.

As far as I know nasm won't do that?

P.S., I assume you're the same Tavis who is known for your FVWM
config?

Hah, yes, that was me :)

Tavis.
--
_o) $ lynx lock.cmpxchg8b.com
/\\ _o) _o) $ finger taviso@sdf.org
_\_V _( ) _( ) @taviso

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From Newsgroup: comp.lang.asm.x86

On 2023-12-02, Tavis Ormandy <taviso@nospicedham.gmail.com> wrote:

On 2023-12-02, Borax Man wrote:

NASM can generate debugging information which I believe will generate
line info. Pass '-F dwarf' option to nasm if under Linux, and you should see each
line of source in the debugger.

You're thinking of line markers I think (like %line 123), but I think
Martijn wants the assembler to do that automatically so that b
foo.asm:123 works, like it does in gas.

As far as I know nasm won't do that?

I did a test using nasm with the '-F dwarf' and '-g' parameters, and I
was able to add breakpoints in GDB specifying the line using the
syntax you mentioned.

I didn't mention "-g" before, oops.

P.S., I assume you're the same Tavis who is known for your FVWM
config?

Hah, yes, that was me :)

Tavis.

Cool. Avid and longtime FVWM user here.

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From Newsgroup: comp.lang.asm.x86

On 2023-12-03, Borax Man wrote:

On 2023-12-02, Tavis Ormandy <taviso@nospicedham.gmail.com> wrote:

On 2023-12-02, Borax Man wrote:

NASM can generate debugging information which I believe will generate
line info. Pass '-F dwarf' option to nasm if under Linux, and you should see each
line of source in the debugger.

You're thinking of line markers I think (like %line 123), but I think
Martijn wants the assembler to do that automatically so that b
foo.asm:123 works, like it does in gas.

As far as I know nasm won't do that?

I did a test using nasm with the '-F dwarf' and '-g' parameters, and I
was able to add breakpoints in GDB specifying the line using the
syntax you mentioned.

Weird.... and this is for elf64?

Perhaps you have a newer version than me, good to know it will arrive eventually!

Tavis.
--
_o) $ lynx lock.cmpxchg8b.com
/\\ _o) _o) $ finger taviso@sdf.org
_\_V _( ) _( ) @taviso

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From Newsgroup: comp.lang.asm.x86

On 3 Dec 2023 16:43:39 GMT
Tavis Ormandy <taviso@nospicedham.gmail.com> wrote:

On 2023-12-03, Borax Man wrote:

On 2023-12-02, Tavis Ormandy <taviso@nospicedham.gmail.com> wrote:

On 2023-12-02, Borax Man wrote:

NASM can generate debugging information which I believe will generate
line info. Pass '-F dwarf' option to nasm if under Linux, and you should see each
line of source in the debugger.

You're thinking of line markers I think (like %line 123), but I think
Martijn wants the assembler to do that automatically so that b
foo.asm:123 works, like it does in gas.

As far as I know nasm won't do that?

I did a test using nasm with the '-F dwarf' and '-g' parameters, and I
was able to add breakpoints in GDB specifying the line using the
syntax you mentioned.

Weird.... and this is for elf64?

Perhaps you have a newer version than me, good to know it will arrive eventually!

Tavis.

I tested this on Debian 12... 32 bit (my laptop is old).


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From Newsgroup: comp.lang.asm.x86

On 2023-12-04, Borax Man <rotflol2@nospicedham.hotmail.com> wrote:

On 3 Dec 2023 16:43:39 GMT
Tavis Ormandy <taviso@nospicedham.gmail.com> wrote:

On 2023-12-03, Borax Man wrote:

On 2023-12-02, Tavis Ormandy <taviso@nospicedham.gmail.com> wrote:

On 2023-12-02, Borax Man wrote:

NASM can generate debugging information which I believe will generate
line info. Pass '-F dwarf' option to nasm if under Linux, and you should see each
line of source in the debugger.

You're thinking of line markers I think (like %line 123), but I think
Martijn wants the assembler to do that automatically so that b
foo.asm:123 works, like it does in gas.

As far as I know nasm won't do that?

I did a test using nasm with the '-F dwarf' and '-g' parameters, and I
was able to add breakpoints in GDB specifying the line using the
syntax you mentioned.

Weird.... and this is for elf64?

Perhaps you have a newer version than me, good to know it will arrive eventually!

Tavis.

I tested this on Debian 12... 32 bit (my laptop is old).

Just to clarify, NASM version 2.16.01.

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From Newsgroup: comp.lang.asm.x86

All,

Reporting back was taking a little longer then I expexted ...sorry.

Anyway.
I still cannot get the debugger to break on a linenumber. If I read correctly you had more luck (or wisdom).

However the method mentioned earlier : x/10i _start does work!

Did really helps me, I was not aware of x being able to display instructions. Then I was able to set a breakpoint on the adress that I need/want.

And now I can start debugging.
Stepping through the program with "s" was running through the program immediately, so I found that I had to use "si" (Step Instruction)

It still seams/seems silly to me that I can list a piece of a program in gdb, but can not set a break on the kines I think trhe debugger knows:

(gdb) list
1 section .data
2
3 section .text
4
5 global _start
6
7 _start:
8 mov al, 1 ; mov 1 into the al register
9
10 mov rax, 60 ; syscall for exit
(gdb) b 8
No line 8 in the current file.
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb)

Anyway....I can dust off some more old assembly knowledge now.


Thanks all for you help and time.

Best Regards,
Martijn



Op maandag 4 december 2023 om 13:12:49 UTC+1 schreef Borax Man:

On 2023-12-04, Borax Man <rotf...@nospicedham.hotmail.com> wrote:

On 3 Dec 2023 16:43:39 GMT
Tavis Ormandy <tav...@nospicedham.gmail.com> wrote:

On 2023-12-03, Borax Man wrote:

On 2023-12-02, Tavis Ormandy <tav...@nospicedham.gmail.com> wrote:

On 2023-12-02, Borax Man wrote:

NASM can generate debugging information which I believe will generate >> >>> line info. Pass '-F dwarf' option to nasm if under Linux, and you should see each
line of source in the debugger.

You're thinking of line markers I think (like %line 123), but I think >> >> Martijn wants the assembler to do that automatically so that b
foo.asm:123 works, like it does in gas.

As far as I know nasm won't do that?

I did a test using nasm with the '-F dwarf' and '-g' parameters, and I >> > was able to add breakpoints in GDB specifying the line using the
syntax you mentioned.

Weird.... and this is for elf64?

Perhaps you have a newer version than me, good to know it will arrive eventually!

Tavis.

I tested this on Debian 12... 32 bit (my laptop is old).

Just to clarify, NASM version 2.16.01.

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