The SoftMMU now receives full X86::LogicalAddress values from SoftCPU.
This allows the MMU to reroute TLS accesses to a special memory region.
The ELF executable's PT_TLS header tells us how to allocate the TLS.
Basically, the GS register points to a magical 4-byte area which has
a pointer to the TCB (thread control block). The TCB lives in normal
flat memory space and is accessed through the DS register.
(And all other memory, too.) This will mutate later when we add shadow
memory etc, but for now just zero-initialize it since that's expected
by the emulated program.
Instead of starting with argv=nullptr, envp=nullptr, programs now
start with both pointing to a null terminated array (that immediately
terminates.) :^)
This patch adds a basic ELF program loader to the UserspaceEmulator and
creates MMU regions for each PT_LOAD header. (Note that we don't yet
respect the R/W/X flags etc.)
We also turn the SoftCPU into an X86::InstructionStream and give it an
EIP register so we can actually execute code by fetching memory through
our MMU abstraction.
This introduces a new X86 CPU emulator for running SerenityOS userspace
programs in a virtualized interpreter environment.
The main goal is to be able to instrument memory accesses and catch
interesting bugs that are very hard to find otherwise. But before we
can do fancy things like that, we have to build a competent emulator
able to actually run programs.
This initial version is able to run a very small program that makes
some tiny syscalls, but nothing more.
