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Kernel: Stop overwriting AArch64 link register in forked processes

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Forked processes already have an existing value for the link register,
which we can't overwrite. But since they're forked the original link
register value that points to exit_kernel_thread was already saved
somewhere on the stack, so it's ok not to set it.
This commit is contained in:
Idan Horowitz 2023-04-02 03:21:24 +03:00 • committed by Andrew Kaster
parent 8669f4ce45
commit 6ad8f4bb11
1 changed files with 7 additions and 2 deletions
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9
Kernel/Arch/aarch64/Processor.cpp
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@ -287,8 +287,13 @@ FlatPtr Processor::init_context(Thread& thread, bool leave_crit)
RegisterState& eretframe = *reinterpret_cast<RegisterState*>(stack_top);
memcpy(eretframe.x, thread_regs.x, sizeof(thread_regs.x));
// x30 is the Link Register for the aarch64 ABI, so this will return to exit_kernel_thread when main thread function returns.
eretframe.x[30] = FlatPtr(&exit_kernel_thread);
// We don't overwrite the link register if it's not 0, since that means this thread's register state was already initialized with
// an existing link register value (e.g. it was fork()'ed), so we assume exit_kernel_thread is already saved as previous LR on the
// stack somewhere.
if (eretframe.x[30] == 0x0) {
// x30 is the Link Register for the aarch64 ABI, so this will return to exit_kernel_thread when main thread function returns.
eretframe.x[30] = FlatPtr(&exit_kernel_thread);
}
eretframe.elr_el1 = thread_regs.elr_el1;
eretframe.sp_el0 = thread_regs.sp_el0;
eretframe.spsr_el1 = thread_regs.spsr_el1;