The boot modules assembled by the generated boot_modules.s file is
accessed from core using struct Bm_header. Unfortunately the assembler
.long directive is synonym to .int [1] and thus has the same size as the
C++ int type and *not* long. Use the matching assembly type .quad in
boot_modules.s when generating the file for 64-bit platforms such as
x86_64.
[1] - https://sourceware.org/binutils/docs/as/Long.html
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