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Editorial Team
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Asked: 2026-05-31T09:25:07+00:00

When using gdb , I often get a nice list of parameters passed to

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When using gdb, I often get a nice list of parameters passed to functions. However, with certain functions like bind, I do not get the parameters:

(gdb) break bind
Breakpoint 1 at 0x404b40
(gdb) r
...
Breakpoint 1, bind () at ../sysdeps/unix/syscall-template.S:82
82      in ../sysdeps/unix/syscall-template.S
(gdb) bt
#0  bind () at ../sysdeps/unix/syscall-template.S:82
...

How can I still get the parameters passed to these functions?

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1 Answer

  1. Editorial Team

    bind is one of socket system calls. There is a special way to put breakpoints on system calls in gdb – catch syscall <syscall name>. After this kind of breakpoint hit, you can watch syscall parameters in registers according to kernel calling conventions. For x86_64, parameters are passed via %rdi, %rsi, %rdx, %r10, %r8 and %r9 registers. For x86-32 – via %ebx, %ecx, %edx, %esi, %edi, %ebp registers.

    (gdb) catch syscall bind 
Catchpoint 3 (syscall 'bind' [49])
(gdb) r
Starting program: /usr/bin/nmap google.com

Starting Nmap 5.00 ( http://nmap.org ) at 2012-03-16 01:09 PDT
Warning: Hostname google.com resolves to 6 IPs. Using 173.194.69.100.

Catchpoint 3 (call to syscall 'bind'), 0x00007ffff6520307 in bind ()
   from /lib/libc.so.6
(gdb) info registers 
rax            0xffffffffffffffda   -38
rbx            0xb35870 11753584
rcx            0xffffffffffffffff   -1
rdx            0x14 20
rsi            0x7fffffff7d90   140737488321936
rdi            0x8  8
rbp            0x8  0x8
rsp            0x7fffffff7d58   0x7fffffff7d58
r8             0xb  11
r9             0x8000   32768
r10            0x7fffffff7b00   140737488321280
r11            0x202    514
r12            0xb09630 11572784
r13            0xb359f0 11753968
r14            0x2  2
r15            0xc8 200
rip            0x7ffff6520307   0x7ffff6520307 <bind+7>
eflags         0x202    [ IF ]
cs             0x33 51
ss             0x2b 43
ds             0x0  0
es             0x0  0
fs             0x0  0
---Type <return> to continue, or q <return> to quit---
gs             0x0  0
(gdb)

    For example here %rdi contains first bind call parameter – socket file descriptor.

    For x86-32 things are more complicated as socket system calls are implemented via socketcall system call. Thats why it’s impossible to put catchpoint directly to bind. You can find more info about it here.

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