48 lines
2.8 KiB
ArmAsm
48 lines
2.8 KiB
ArmAsm
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# as --32 hello-x86-32.s && ld.gold -m32 -s -n -o hello a.out
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.data # section declaration
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msg:
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.string "All your codebase is belong to us\n" # our dear string
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len = . - msg # length of our dear string
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.text # section declaration
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# we must export the entry point to the ELF linker or
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.global _start # loader. They conventionally recognize _start as their
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# entry point. Use ld −e foo to override the default.
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# https://stackoverflow.com/questions/3683144/linux-64-command-line-parameters-in-assembly
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# https://wiki.cdot.senecacollege.ca/wiki/X86_64_Register_and_Instruction_Quick_Start
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square:
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pushl %ebp # Save ebp - this must be restored at end of call
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movl %esp, %ebp # Update base pointer from current stack pointer
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# 8 bytes above ebp is our first parameter
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# (4 bytes above is our return address)
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# In this case, _start is not explictly adding
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# our parameter to the stack as that is being
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# done prior to us being exec'd in the first place
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# There is a good diagram of this in the calling
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# convention section on https://www.cs.virginia.edu/~evans/cs216/guides/x86.html
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movl 8(%ebp), %eax # Move stack memory into eax for multiplication
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imull 8(%ebp), %eax # Do multiplication
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popl %ebp # Restore rbp for return (eax/rax has return val)
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ret # Return
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_start:
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# Linux syscalls for 32 bit:
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# https://github.com/torvalds/linux/blob/master/arch/x86/entry/syscalls/syscall_32.tbl
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# write our string to stdout
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movl $4,%eax # system call number (sys_write)
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movl $1,%ebx # first argument: file handle (stdout)
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movl $msg,%ecx # second argument: pointer to message to write
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movl $len,%edx # third argument: message length
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int $0x80 # call kernel and exit
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# argc is stored in (%esp)
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movl (%esp),%edi # See: https://wiki.cdot.senecacollege.ca/wiki/X86_64_Register_and_Instruction_Quick_Start
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# The above instruction is part of the calling convention,
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# so left here, but it's useless/unnecessary and can be removed
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call square # Square our argc, result in %eax
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movl %eax,%ebx # mov %eax to the first syscall argument (exit code)
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movl $1,%eax # system call number (sys_exit)
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int $0x80 # call kernel
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