Can I exec an new process without an executable file? (2015)

Re:Can I exec an new process without an executable file? (2015) by anshargal on Thursday November 03, 2022 @06:07AM (#33449014)

I had to add

  #define _GNU_SOURCE
  #include <sys/mman.h>
  #include <unistd.h>

I've tested in Fabrice Bellard JSLinux with tcc (x86 arch) and on https://replit.com/languages/c (x64). I failed to see any side effect at all. gdb "catch syscall" doesn't show anything interesting too. Looks like TINY_ELF_PROGRAM is not doing anything.

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Re:Can I exec an new process without an executable file? (2015) by enriquto on Thursday November 03, 2022 @06:15AM (#33449038)

you can disassemble the code portion, they are single-byte instructions

    push 0x2a
    pop edi
    push 0x3c
    pop eax
    db 0x0f, 0x05 ; invalid?

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Re:Can I exec an new process without an executable file? (2015) by qguv on Thursday November 03, 2022 @06:32AM (#33449124)

    ; set the first syscall argument to 42
    push   0x2a
    pop    edi

    ; select syscall 60 (sys_exit)
    push   0x3c
    pop    eax

    ; sys_exit(42)
    syscall

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Re:Can I exec an new process without an executable file? (2015) by enriquto on Thursday November 03, 2022 @06:37AM (#33449162)

LOL my asm is rusty, didn't even know about the syscall instruction (I'd have used int 0x80 here)

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Re:Can I exec an new process without an executable file? (2015) by mFixman on Thursday November 03, 2022 @09:56AM (#33451027)

What's the point of `push`ing constants to the stack and `pop`ing them to registers instead of `mov`ing them directly?

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Re:Can I exec an new process without an executable file? (2015) by saagarjha on Thursday November 03, 2022 @11:01AM (#33452065)

I think they encode smaller?

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Re:Can I exec an new process without an executable file? (2015) by anshargal on Thursday November 03, 2022 @10:00AM (#33451098)

That's cool - I wonder why exit code is not set to 42 in practice? binary still returns 0, must be a bug somewhere.

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Re:Can I exec an new process without an executable file? (2015) by saagarjha on Thursday November 03, 2022 @11:01AM (#33452060)

A successful run not exiting with EXIT_SUCCESS usually requires a good reason to justify it.

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