arch-x86: Add allocator for ACPI tables

This adds an allocator class to allocate memory linearly. It is intended
to be used by ACPI tables to dynamically request memory to write the
ACPI tables to.

Change-Id: I43c71d2b8e676f8ac0fd08b9468b00b6212d85b6
Signed-off-by: Maximilian Stein <m@steiny.biz>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42823
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/x86/bios/acpi.cc

@@ -45,6 +45,20 @@
 #include "sim/byteswap.hh"
 #include "sim/sim_object.hh"
 
+Addr
+X86ISA::ACPI::LinearAllocator::alloc(std::size_t size, unsigned align)
+{
+    if (align) {
+        unsigned offset = next % align;
+        if (offset)
+            next += (align - offset);
+    }
+    Addr chunk = next;
+    next += size;
+    assert(0 == end || next <= end);
+    return chunk;
+}
+
 const char X86ISA::ACPI::RSDP::signature[] = "RSD PTR ";
 
 X86ISA::ACPI::RSDP::RSDP(const Params &p) : SimObject(p), oemID(p.oem_id),

src/arch/x86/bios/acpi.hh

@@ -62,6 +62,24 @@ class RSDT;
 class XSDT;
 class SysDescTable;
 
+struct Allocator
+{
+    virtual Addr alloc(std::size_t size, unsigned align=1) = 0;
+};
+struct LinearAllocator : public Allocator
+{
+    LinearAllocator(Addr begin, Addr end=0) :
+        next(begin),
+        end(end)
+    {}
+
+    Addr alloc(std::size_t size, unsigned align) override;
+
+  protected:
+    Addr next;
+    Addr const end;
+};
+
 class RSDP : public SimObject
 {
   protected: