How can I assemble a minimal working MIPS program?

Question

I can run this assembly code in my simulator but I get a linker warning

Linking...
ld: warning: cannot find entry symbol start; defaulting to 80020000
Post build...

Done

Why do I get this error with solely the assembly code and not with C code that does the same? How can I change my assembly to make the linker happy? I'd like to know which statements are not necessary so that I can have a minimal program?

I could comment out these statement (that I'm not sure what they do):

#.frame $fp,40,$31      # vars= 16, regs= 2/0, args= 16, extra= 0
#.mask  0xc0000000,-4
#.fmask 0x00000000,0

My code (that was translated from C) is

    .file   1 "minimips.c"

 # -G value = 8, Cpu = 3000, ISA = 1
 # GNU C version cygnus-2.7.2-970404 (mips-mips-ecoff) compiled by GNU C version cygnus-2.7.2-970404.
 # options passed:  -msoft-float
 # options enabled:  -fpeephole -ffunction-cse -fkeep-static-consts
 # -fpcc-struct-return -fcommon -fverbose-asm -fgnu-linker -msoft-float
 # -meb -mcpu=3000

gcc2_compiled.:
__gnu_compiled_c:
    .rdata
    .align  2
$LC0:
    .ascii  "Result %d\000"
    .text
    .align  2
    .globl  main
    .ent    main
main:
    #.frame $fp,40,$31      # vars= 16, regs= 2/0, args= 16, extra= 0
    #.mask  0xc0000000,-4
    #.fmask 0x00000000,0
    subu    $sp,$sp,40
    sw  $31,36($sp)
    sw  $fp,32($sp)
    move    $fp,$sp
    jal __main
    li  $2,40           
    sw  $2,16($fp)
    li  $2,40           
    sw  $2,20($fp)
    lw  $2,16($fp)
    lw  $3,20($fp)
    addu    $2,$2,$3
    sw  $2,24($fp)
    la  $4,$LC0
    lw  $5,24($fp)
    jal printf
    move    $2,$0
    j   $L1
$L1:
    move    $sp,$fp         # sp not trusted here
    lw  $31,36($sp)
    lw  $fp,32($sp)
    addu    $sp,$sp,40
    j   $31
    .end    main

To begin with I'm just adding numbers. The C code was a+b=c.

Update

When I translated a simpler program (without any includes) then I can create a project type assembly (and not combined C/asm).

It now compiles and runs without linker error (but it doesn't use printf)

gcc2_compiled.:
__gnu_compiled_c:
    .text
    .align  2
    .globl  main
    .ent    main
main:
    .frame  $fp,40,$31      # vars= 16, regs= 2/0, args= 16, extra= 0
    .mask   0xc0000000,-4
    .fmask  0x00000000,0
    subu    $sp,$sp,40
    sw  $31,36($sp)
    sw  $fp,32($sp)
    move    $fp,$sp
    jal __main
    li  $2,15           # 0x0000000a
    sw  $2,16($fp)
    li  $2,20           # 0x00000014
    sw  $2,20($fp)
    lw  $2,16($fp)
    lw  $3,20($fp)
    addu    $2,$2,$3
    sw  $2,24($fp)
    move    $2,$0
    j   $L1
$L1:
    move    $sp,$fp         # sp not trusted here
    lw  $31,36($sp)
    lw  $fp,32($sp)
    addu    $sp,$sp,40
    j   $31
    .end    main

Answer 1

The C library defines a special symbol called start which is where the program starts execution. The linker expects to find this symbol, which it will use as the program entry point.

You didn't define start so the linker complains and gives you a default value. The default is probably the first instruction of your code, so that's why the program still works.