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Define a new "ZREL" compressor information block, describing a block of Elf_Rel or Elf_Rela runtime relocations to be converted to an iPXE-specific compressed relocation format. The compressed relocation format is based loosely on the Elf_Relr bitmap+offset format, with some optimisations for use in iPXE. In particular: - a relative "skip" value is used instead of an absolute offset - the width of the skip value is reduced to 19 bits (when present) - an explicit skip value of zero is used to terminate the list - unaligned relocations are prohibited The layout of bits within the compressed relocation record is also adjusted to make assembly code implementations simpler: the skip flag bit is placed in the MSB so that it can be tested using "bltz" or similar instructions, and the skip value is placed above the relocation flag bits so that a typical shifting implementation will naturally end up with a zero value in its accumulator if and only if the record was a terminator. Signed-off-by: Michael Brown <mcb30@ipxe.org>
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