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Asked: 2011-11-09 19:05:35 +0800 CST

Is there a way to make objdump read from STDIN instead of a file?

  • 772

In my specific case, I want to use it to dump what I echo.
I don't want to involve any file...
Is there a way to make objdump read from STDIN instead?

linux bash stdin

4 Answers

  1. You can't. There is no way around that, you will have to use the temporary file.

    Source file readelf.c has this unconditional check (in binutils 2.22-8 at least) before even attempting to open the file:

    if (! S_ISREG (statbuf.st_mode))
    {
      error (_("'%s' is not an ordinary file\n"), file_name);
      return 1;
    }

    So if the file is anything but regular file (like symlink, or char device as in case of /dev/stdin, /proc/self/fd/*, etc.) it won't work.

    Alternatively, you could modify the source and use modified objdump, but there goes your portability.

    • 8

  2. you can always do

    objdump -d /dev/stdin < t2.o

    or

    cat t2.o | objdump -d /dev/stdin

    sample

    [root@myhost cc]# objdump -h /dev/stdin < t2.o

    /dev/stdin: file format elf64-x86-64

    Sections: Idx Name Size VMA LMA
    File off Algn 0 .group 00000008 0000000000000000 0000000000000000 00000040 2**2 CONTENTS, READONLY, EXCLUDE, GROUP, LINK_ONCE_DISCARD

    • 4

  3. I used ndisasm -b 64 - as a workaround.

    e.g. I wanted:

    echo 41 89 1b | xxd -r -p | objdump -d -

    But the above doesn't work. This does work though:

    echo 41 89 1b | xxd -r -p | ndisasm -b 64 -

    • 0

  4. A kind of workaround is using tee. So to disassemble a file named input use

    cat input | tee a.out | objdump -d

    And, to give an example for passing some bytes with the echo command, the following should be a good example (The parameters are described in this good SO answer):

    To disassemble the x86 code byte sequence

    b8 01 00 00 00 bb 0a 00 00 00 cd 80

    prefix it with 0: and use the command

    echo "0: b8 01 00 00 00 bb 0a 00 00 00 cd 80" | xxd -r | tee a.out | objdump -D -Mintel,i386 -b binary -m i386

    Its output is:

    a.out:     file format binary
Disassembly of section .data:
00000000 <.data>:
   0:   b8 01 00 00 00          mov    eax,0x1
   5:   bb 0a 00 00 00          mov    ebx,0xa
   a:   cd 80                   int    0x80

    which is just the assembly code for exiting an i386 linux program with the exit code 0xA.

    • -1