Why do the different debuggers output different assembly code for the same function?

Question

I write a simple C program in Solaris and want to check the assembly code of dup:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char **argv)
{
        int pdes[2];


        if(-1 != (pipe(pdes)))
        {
                //printf("%d\n", dup(pdes[0]));
                dup(pdes[0]);
        }

        return 0;
}

(1) I use gdb, and gdb outputs the assembly code:

(gdb) disassemble dup
Dump of assembler code for function dup:
   0xff2cda44 <+0>:     mov  0x29, %g1  ! 0x29
   0xff2cda48 <+4>:     ta  8
   0xff2cda4c <+8>:     bcs  0xff223be0 <_cerror>
   0xff2cda50 <+12>:    nop
   0xff2cda54 <+16>:    retl
   0xff2cda58 <+20>:    nop
End of assembler dump.

(2) I use mdb, and mdb outputs the assembly code:

> dup::dis
PLT:dup:                        sethi     %hi(0x21000), %g1
PLT:dup:                        ba,a      -0x88         <0x20a14>
PLT:dup:                        nop
0x20aa4:                        nop
0x20aa8:                        unimp     0x1
0x20aac:                        unimp     0xe0
0x20ab0:                        unimp     0xc
0x20ab4:                        unimp     0x109b8
0x20ab8:                        unimp     0xd
0x20abc:                        unimp     0x109d4
0x20ac0:                        unimp     0x1d

(3) I use the command: echo "dup::dis" | mdb -k, and the assembly code:

dup:                            sra       %o0, 0x0, %o0
dup+4:                          mov       %o7, %g1
dup+8:                          clr       %o2
dup+0xc:                        clr       %o1
dup+0x10:                       call      -0xeec        <fcntl>
dup+0x14:                       mov       %g1, %o7

Why do the three methods output different assembly code for the same function?

Answer 1

Case (1) shows the disassembly for the actual function.

Case (2) shows the PLT (procedure linkage table) entry for the function. The PLT is used to resolve functions imported from shared libraries. This is used by the main program when it invokes the function. Code flow will eventually end up in the real function, of course, through the help of the runtime linker.

Case (3): I have no idea what this is.