26bca020b6
Nexoniarz is the sole author and SchOS was never published under Apache-2.0, so this is a straight relicence. LICENSE is the FSF GPLv2 text, every first-party SPDX header moves to GPL-2.0-or-later, and NOTICE, README.md, docs/licensing.md and the site say so. projects/schfs-linux follows the rest of the tree. The GPL gives copyleft: a fork has to ship its source. It also lifts the old "Linux drivers, never" rule, since GPL-2.0-only code combines with GPL-2.0-or-later. "Or later" leaves room for GPLv3, but one binary still has to pick one version, so docs/licensing.md now keeps Apache-2.0 and GPLv3 code out of the kernel to keep Linux code possible there. BSD 4-clause code goes from "avoid" to "no", because the advertising clause is GPL-incompatible. LDLS still ships no .ko. That boundary is now project policy rather than a legal requirement, and ldls.md, devices.md and licensing.md section 6 say so. refmod declares license=GPL, and ldls-check passes (27 checks). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
56 lines
2.4 KiB
ArmAsm
56 lines
2.4 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0-or-later
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* SchOS — process entry point.
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*
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* This has to be assembly, and the reason is worth recording.
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*
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* exec() hands a new process its arguments in registers, not on the stack:
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* kernel/fs/exec.c sets proc->tf->rdi = argc and proc->tf->rsi = argv. Those
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* are already the first two SysV argument registers, so _start's entire job
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* is to call main and then exit — it must not touch %rdi or %rsi at all.
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*
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* It used to be written in C, capturing the incoming registers with GCC's
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*
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* register int argc_reg asm("rdi");
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*
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* That is not what local register variables mean. Both GCC and clang only
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* guarantee the binding when the variable is used as an operand of an inline
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* asm statement; reading one to pick up an incoming argument is undefined.
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* GCC happened to do the useful thing. clang compiled it to
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*
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* movl -0x4(%rbp), %eax # two uninitialised stack slots
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* movq -0x10(%rbp), %rax
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*
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* and every program was handed a garbage argc and argv. Nothing crashed --
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* init, shmtest and socktest take no arguments and passed their whole test
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* suites -- so the only symptom was `inputtest -n 6` quietly ignoring its
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* limit. A compiler-dependent way to read registers has no business being in
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* C when four instructions of assembly are exactly right.
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*/
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.text
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.globl _start
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_start:
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xorq %rbp, %rbp /* end the frame-pointer chain here */
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/* SysV wants %rsp 16-byte aligned immediately before a call, so that the
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* callee sees %rsp+8 aligned once the return address is pushed. Rounding
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* down is safe: argc and argv arrive in registers, so nothing below is
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* needed. */
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andq $-16, %rsp
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callq main /* main(%rdi = argc, %rsi = argv) */
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/* main's return value is the exit status, and it used to be thrown away.
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*
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* sys_exit() reads the status from %rdi, and nothing put it there -- so
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* every first-party program exited with whatever happened to be in that
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* register, and `if socktest; then` could not work for any of them. The
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* test suites all end in `return failures ? 1 : 0` and none of it reached
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* the shell.
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*
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* %eax, not %rax: the status is the low eight bits, and a `return 0` from
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* a C function leaves only %eax defined. */
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movl %eax, %edi
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callq exit_group /* noreturn, but be certain */
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1: hlt
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jmp 1b
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