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On a 64-bit CPU, any modification of a register by 32-bit or 16-bit code will destroy the invisible upper 32 bits of the corresponding 64-bit register. For example: a 32-bit "pushl %eax" followed by a "popl %eax" will zero the upper half of %rax. This differs from the treatment of upper halves of 32-bit registers by 16-bit code: a "pushw %ax" followed by a "popw %ax" will leave the upper 16 bits of %eax unmodified. Inline assembly generated using REAL_CODE() or PHYS_CODE() will therefore have to preserve the upper halves of all registers, to avoid clobbering registers that gcc expects to be preserved. Output operands from REAL_CODE() and PHYS_CODE() assembly may therefore contain undefined values in the upper 32 bits. Fix by using explicit variable widths (e.g. uint32_t) for non-discarded output operands, to ensure that undefined values in the upper 32 bits of 64-bit registers are ignored. Signed-off-by: Michael Brown <mcb30@ipxe.org>
iPXE README File Quick start guide: cd src make For any more detailed instructions, see http://ipxe.org