meaning of objdump -d output assembly

Question

I'm trying to figure out what all of the elements of this objdump -d mean.

for example i have:

08048b50 <phase_1>:
8048b50:    83 ec 1c                sub    $0x1c,%esp
 8048b53:   c7 44 24 04 68 a2 04    movl   $0x804a268,0x4(%esp)
 8048b5a:   08 
 8048b5b:   8b 44 24 20             mov    0x20(%esp),%eax
 8048b5f:   89 04 24                mov    %eax,(%esp)
 8048b62:   e8 63 04 00 00          call   8048fca <strings_not_equal>
 8048b67:   85 c0                   test   %eax,%eax
 8048b69:   74 05                   je     8048b70 <phase_1+0x20>
 8048b6b:   e8 f5 06 00 00          call   8049265 <explode_bomb>
 8048b70:   83 c4 1c                add    $0x1c,%esp
 8048b73:   c3                      ret    

specifically im not sure what the 1st and center columns are telling me

Answer 1

The first column tells you the memory addresses where the code will be located at runtime.

The second column has the hex version of the executable instruction.

The third (and forth) columns, have a disassembled version of the second column. i.e. opcode and operands.

Answer 2

first : address, hex. The difference between two adjacent addresses is the number of machine codes.

second : Machine code, hex.

third : Assembler code, disassembled from machine code.

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execute 'objdump -no-leading-addr -S **.o', the first column will be hidden.

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objdump --version Apple LLVM version 11.0.0 (clang-1100.0.33.17)