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Portability EN
Language: English ｜ Portability
The tree builds on GCC 14.x locally and on newer toolchains on CI. Three classes of difference have already bitten - keep them in mind:
-Waddress-of-packed-member (part of -Wall since GCC 9, enforced
harder on newer releases): casting a packed-struct pointer to a
naturally-aligned type is an error under -Werror. The multiboot2
tag types are ALL declared __attribute__((packed)) for exactly this
reason - including the mmap tag (4x u32, no layout change) and the
BASIC_MEMINFO reader which goes through a packed tag type instead of
a bare u32* cast.
Rule: when you cast a pointer that came from packed memory, target a packed type.
setcc/setc accept BYTE registers only. The rdrand wrapper
declared its flag as u32 with an "=q" constraint - older GAS
silently truncated to the byte subregister, newer GAS rejects the
operand size. It is u8 now.
Rule: setcc-style flags are u8, constraint "=q".
OC_TOOLS may point at a relocatable tree (<root>/usr/{bin,lib})
OR a system root (/usr with {bin,lib} directly under it). The
embed_grub generator probes both layouts - do not assume either one.
The kernel flags are fixed in the Makefile:
-ffreestanding -fno-stack-protector -fno-pie -fno-pic -mno-red-zone -mno-sse -mno-mmx -mno-3dnow -mcmodel=kernel -fno-asynchronous-unwind-tables -Wall -Wextra -Werror -O2 -g -std=gnu11. New flags belong in the Makefile (one place), not
scattered in files.
make ARCH=arm64 / ARCH=riscv use the aarch64/riscv64 cross
toolchains and their own linker rules (--hash-style=sysv --build-id=none; -n and PHDR layouts do not mix). The bring-up
shells are real (PL011/NS16550A divisors, timer counters, heartbeat)
but deliberately minimal - x86_64 is the feature-complete
architecture.