On Wed, May 22, 2013 at 10:12 PM, John Reiser <jreiser@xxxxxxxxxxxx> wrote: > 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. Which means you'd be better off with file system level compression. -- test mailing list test@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe: https://admin.fedoraproject.org/mailman/listinfo/test
