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Kernel: Support thread-local storage

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This patch adds support for TLS according to the x86 System V ABI.
Each thread gets a thread-specific memory region, and the GS segment
register always points _to a pointer_ to the thread-specific memory.

In other words, to access thread-local variables, userspace programs
start by dereferencing the pointer at [gs:0].

The Process keeps a master copy of the TLS segment that new threads
should use, and when a new thread is created, they get a copy of it.
It's basically whatever the PT_TLS program header in the ELF says.
This commit is contained in:
Andreas Kling 2019-09-07 15:50:44 +02:00
parent bcfdf9ffa7
commit ec6bceaa08
7 changed files with 92 additions and 5 deletions
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6
Kernel/Scheduler.cpp
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@ -460,6 +460,12 @@ bool Scheduler::context_switch(Thread& thread)
descriptor.descriptor_type = 0;
}
if (!thread.thread_specific_data().is_null()) {
auto& descriptor = thread_specific_descriptor();
descriptor.set_base(thread.thread_specific_data().as_ptr());
descriptor.set_limit(sizeof(ThreadSpecificData*));
}
auto& descriptor = get_gdt_entry(thread.selector());
descriptor.type = 11; // Busy TSS
flush_gdt();