| 1 | sstrip is a small utility that removes the contents at the end of an
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| 2 | ELF file that are not part of the program's memory image.
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| 3 |
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| 4 | Most ELF executables are built with both a program header table and a
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| 5 | section header table. However, only the former is required in order
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| 6 | for the OS to load, link and execute a program. sstrip attempts to
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| 7 | extract the ELF header, the program header table, and its contents,
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| 8 | leaving everything else in the bit bucket. It can only remove parts of
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| 9 | the file that occur at the end, after the parts to be saved. However,
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| 10 | this almost always includes the section header table, and occasionally
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| 11 | a few random sections that are not used when running a program.
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| 12 |
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| 13 | It should be noted that the GNU bfd library is (understandably)
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| 14 | dependent on the section header table as an index to the file's
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| 15 | contents. Thus, an executable file that has no section header table
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| 16 | cannot be used with gdb, objdump, or any other program based upon the
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| 17 | bfd library, at all. In fact, the program will not even recognize the
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| 18 | file as a valid executable. (This limitation is noted in the source
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| 19 | code comments for bfd, and is marked "FIXME", so this may change at
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| 20 | some future date. However, I would imagine that it is a pretty
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| 21 | low-priority item, as executables without a section header table are
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| 22 | rare in the extreme.) This probably also explains why strip doesn't
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| 23 | offer the option to do this.
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| 24 |
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| 25 | Shared library files may also have their section header table removed.
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| 26 | Such a library will still function; however, it will no longer be
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| 27 | possible for a compiler to link a new program against it.
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| 28 |
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| 29 | As an added bonus, sstrip also tries to removes trailing zero bytes
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| 30 | from the end of the file. (This normally cannot be done with an
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| 31 | executable that has a section header table.)
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| 32 |
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| 33 | sstrip is a very simplistic program. It depends upon the common
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| 34 | practice of putting the parts of the file that contribute to the
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| 35 | memory image at the front, and the remaining material at the end. This
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| 36 | permits it to discard the latter material without affecting file
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| 37 | offsets and memory addresses in what remains. However, the ELF
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| 38 | standard permits files to be organized in almost any order. So
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| 39 | although this procedure usually works in practice, it is not meant to
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| 40 | be taken too seriously.
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