On 05/22/2013 12:04 PM, Clemens Eisserer wrote: > As UPX requires executeables to be decompressed during startup (and > furthermore does not support ELF shared libraries), An executable main program which has been compressed by UPX *can* use ELF shared libraries, and nearly all programs on Linux that are compressed by UPX *do* use shared libraries. The execution-time difference between a compressed and a never- compressed program is that the Linux kernel loads the PT_INTERP for execve() of a regular program, while the UPX runtime stub loads the PT_INTERP for a compressed program. With respect to byte values, there is essentially no difference in the memory image of the process. On a few platforms (including Linux i386 and x86_64) UPX also can compress a shared library itself. You don't get any actual sharing of execution-time pages, but storage space in the filesystem is less. Compression is not as tight as with a main program, because in a shared library only instructions can be compressed: not symbol tables, not .data, etc, because these are needed by ld-linux to perform relocation which happens before UPX can gain control (which it does via DT_INIT.) > its not a sane > option for a distribution. It depends on the desired goals. On distribution media, .rpm packages are compressed using xz (lzma2), and the space saved by xz compression often is similar to that saved by UPX. Once installed, the UPX compression saves storage space in the filesystem at the cost of no sharing: not among multiple simultaneous processes, nor demand paged between the filesystem and process memory space. [I am the maintainer of UPX for ELF.] -- -- test mailing list test@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe: https://admin.fedoraproject.org/mailman/listinfo/test
