10

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?

zx485
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omg
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4 Answers4

8

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.

Matija Nalis
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4

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

user237419
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    `cat t2.o | objdump -d /dev/stdin` does not work. `/dev/stdin` only works when it corresponds to a real file. Since your solution requires the presence of that file, this does not answer the OP. – dragonroot Nov 09 '12 at 05:04
  • This may work for this invocation of `objdump` in particular, but it might fail for others in case it does `seek` operations on the file. When tools don't have `-` for stdin, that is often the case. – Ciro Santilli OurBigBook.com Aug 28 '15 at 09:18
0

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 -

Emil Mikulic
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-1

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.

zx485
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