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sstrip is a small utility that removes the contents at the end of an
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ELF file that are not part of the program's memory image.
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Most ELF executables are built with both a program header table and a
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section header table. However, only the former is required in order
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for the OS to load, link and execute a program. sstrip attempts to
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extract the ELF header, the program header table, and its contents,
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leaving everything else in the bit bucket. It can only remove parts of
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the file that occur at the end, after the parts to be saved. However,
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this almost always includes the section header table, and occasionally
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a few random sections that are not used when running a program.
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It should be noted that the GNU bfd library is (understandably)
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dependent on the section header table as an index to the file's
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contents. Thus, an executable file that has no section header table
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cannot be used with gdb, objdump, or any other program based upon the
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bfd library, at all. In fact, the program will not even recognize the
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file as a valid executable. (This limitation is noted in the source
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code comments for bfd, and is marked "FIXME", so this may change at
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some future date. However, I would imagine that it is a pretty
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low-priority item, as executables without a section header table are
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rare in the extreme.) This probably also explains why strip doesn't
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offer the option to do this.
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Shared library files may also have their section header table removed.
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Such a library will still function; however, it will no longer be
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possible for a compiler to link a new program against it.
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As an added bonus, sstrip also tries to removes trailing zero bytes
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from the end of the file. (This normally cannot be done with an
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executable that has a section header table.)
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sstrip is a very simplistic program. It depends upon the common
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practice of putting the parts of the file that contribute to the
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memory image at the front, and the remaining material at the end. This
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permits it to discard the latter material without affecting file
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offsets and memory addresses in what remains. Of course, the ELF
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standard permits files to be organized in almost any order, so if a
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pathological linker decided to put its section headers at the top,
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sstrip would be useless on such executables.
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src/stub/util/sstrip/README
