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The QEMU_LOADER_WRITE_POINTER command instructs the firmware to write the address of a field within a previously allocated/downloaded fw_cfg blob into another (writeable) fw_cfg file at a specific offset. Put differently, QEMU_LOADER_WRITE_POINTER propagates, to QEMU, the address that QEMU_LOADER_ALLOCATE placed the designated fw_cfg blob at, as adjusted for the given field inside the allocated blob. The implementation is similar to that of QEMU_LOADER_ADD_POINTER. Since here we "patch" a pointer object in "fw_cfg file space", not guest memory space, we utilize the QemuFwCfgSkipBytes() and QemuFwCfgWriteBytes() APIs completed in commit range 465663e9f128..7fcb73541299. An interesting aspect is that QEMU_LOADER_WRITE_POINTER creates a host-level reference to a guest memory location. Therefore, if we fail to process the linker/loader script for any reason, we have to clear out those references first, before we release the guest memory allocations in response to the error. Cc: Jordan Justen <jordan.l.justen@intel.com> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=359 Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Laszlo Ersek <lersek@redhat.com> Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>