From 9b6464010f939893bdf7862e206f1704c5185cb6 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Mon, 13 Jul 2020 11:58:58 +0200
Subject: [PATCH] UserspaceEmulator: Add basic support for memory-mapped files

MmapRegion now supports using an mmap'ed file descriptor as backing.
---
 DevTools/UserspaceEmulator/Emulator.cpp   |  6 ++++--
 DevTools/UserspaceEmulator/MmapRegion.cpp | 23 +++++++++++++++++++++--
 DevTools/UserspaceEmulator/MmapRegion.h   |  6 +++++-
 3 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/DevTools/UserspaceEmulator/Emulator.cpp b/DevTools/UserspaceEmulator/Emulator.cpp
index a1dca6bc5c..8fdad15d16 100644
--- a/DevTools/UserspaceEmulator/Emulator.cpp
+++ b/DevTools/UserspaceEmulator/Emulator.cpp
@@ -309,7 +309,6 @@ u32 Emulator::virt$mmap(u32 params_addr)
     mmu().copy_from_vm(&params, params_addr, sizeof(params));
 
     ASSERT(params.addr == 0);
-    ASSERT(params.flags & MAP_ANONYMOUS);
 
     // FIXME: Write a proper VM allocator
     static u32 next_address = 0x30000000;
@@ -326,7 +325,10 @@ u32 Emulator::virt$mmap(u32 params_addr)
 
     next_address = final_address + final_size;
 
-    mmu().add_region(make<MmapRegion>(final_address, final_size, params.prot));
+    if (params.flags & MAP_ANONYMOUS)
+        mmu().add_region(MmapRegion::create_anonymous(final_address, final_size, params.prot));
+    else
+        mmu().add_region(MmapRegion::create_file_backed(final_address, final_size, params.prot, params.flags, params.fd, params.offset));
 
     return final_address;
 }
diff --git a/DevTools/UserspaceEmulator/MmapRegion.cpp b/DevTools/UserspaceEmulator/MmapRegion.cpp
index 9ea41752e1..18c65f1e0d 100644
--- a/DevTools/UserspaceEmulator/MmapRegion.cpp
+++ b/DevTools/UserspaceEmulator/MmapRegion.cpp
@@ -30,16 +30,35 @@
 
 namespace UserspaceEmulator {
 
+NonnullOwnPtr<MmapRegion> MmapRegion::create_anonymous(u32 base, u32 size, u32 prot)
+{
+    auto region = adopt_own(*new MmapRegion(base, size, prot));
+    region->m_file_backed = false;
+    region->m_data = (u8*)calloc(1, size);
+    return region;
+}
+
+NonnullOwnPtr<MmapRegion> MmapRegion::create_file_backed(u32 base, u32 size, u32 prot, int flags, int fd, off_t offset)
+{
+    auto region = adopt_own(*new MmapRegion(base, size, prot));
+    region->m_file_backed = true;
+    region->m_data = (u8*)mmap(nullptr, size, prot, flags, fd, offset);
+    ASSERT(region->m_data != MAP_FAILED);
+    return region;
+}
+
 MmapRegion::MmapRegion(u32 base, u32 size, int prot)
     : Region(base, size)
     , m_prot(prot)
 {
-    m_data = (u8*)calloc(1, size);
 }
 
 MmapRegion::~MmapRegion()
 {
-    free(m_data);
+    if (m_file_backed)
+        munmap(m_data, size());
+    else
+        free(m_data);
 }
 
 u8 MmapRegion::read8(FlatPtr offset)
diff --git a/DevTools/UserspaceEmulator/MmapRegion.h b/DevTools/UserspaceEmulator/MmapRegion.h
index ed2c8f91ce..d88e325f0a 100644
--- a/DevTools/UserspaceEmulator/MmapRegion.h
+++ b/DevTools/UserspaceEmulator/MmapRegion.h
@@ -33,7 +33,8 @@ namespace UserspaceEmulator {
 
 class MmapRegion final : public SoftMMU::Region {
 public:
-    MmapRegion(u32 base, u32 size, int prot);
+    static NonnullOwnPtr<MmapRegion> create_anonymous(u32 base, u32 size, u32 prot);
+    static NonnullOwnPtr<MmapRegion> create_file_backed(u32 base, u32 size, u32 prot, int flags, int fd, off_t offset);
     virtual ~MmapRegion() override;
 
     virtual u8 read8(u32 offset) override;
@@ -51,8 +52,11 @@ public:
     bool is_executable() const { return m_prot & PROT_EXEC; }
 
 private:
+    MmapRegion(u32 base, u32 size, int prot);
+
     u8* m_data { nullptr };
     int m_prot { 0 };
+    bool m_file_backed { false };
 };
 
 }