From 997e901497eefaf3eb879adc40c2e63f59bc2ef9 Mon Sep 17 00:00:00 2001
From: Abel Shields <admin@nabushika.com>
Date: Tue, 12 Oct 2021 17:30:47 +0100
Subject: [PATCH] Added a dynamic memory implementation using mmap

---
 examples/dynamic-memory.porth | 44 ++++++++++++++++++++++
 std/dynamic-memory.porth      | 70 +++++++++++++++++++++++++++++++++++
 std/std.porth                 |  6 +++
 3 files changed, 120 insertions(+)
 create mode 100644 examples/dynamic-memory.porth
 create mode 100644 std/dynamic-memory.porth

diff --git a/examples/dynamic-memory.porth b/examples/dynamic-memory.porth
new file mode 100644
index 00000000..2b1910b6
--- /dev/null
+++ b/examples/dynamic-memory.porth
@@ -0,0 +1,44 @@
+include "std.porth"
+include "dynamic-memory.porth"
+
+// Test raw memory allocation
+"Allocating memory without housekeeping\n" puts
+
+4096 palloc_raw
+"Pointer: " puts
+dup print
+
+4096 palloc_raw
+"Pointer: " puts
+dup print
+
+// is the difference equal to page size?
+"Difference: " puts
+over over - abs
+print
+"(should be =4096 if addresses aren't randomized)\n" puts
+// CLEAN UP!
+4096 pfree_raw
+4096 pfree_raw // needs to take the size
+
+"\n" puts
+
+// Test housekeeping
+"Allocating memory with housekeeping\n" puts
+
+4096 palloc
+"Pointer: " puts
+dup print
+
+4096 palloc
+"Pointer: " puts
+dup print
+
+// is the difference the page size?
+"Difference: " puts
+over over - abs
+print
+"(should be >4096 due to housekeeping)\n" puts
+// clean up - no need to worry about size
+pfree
+pfree
diff --git a/std/dynamic-memory.porth b/std/dynamic-memory.porth
new file mode 100644
index 00000000..dc80b972
--- /dev/null
+++ b/std/dynamic-memory.porth
@@ -0,0 +1,70 @@
+// requires std.porth - currently there's no include guards so do this yourself!
+
+// TODO: Get from include files, or run C preprocessor?
+macro PROT_READ 1 end
+macro PROT_WRITE 2 end
+macro MAP_PRIVATE 2 end
+macro MAP_ANONYMOUS 32 end
+
+macro exit_if_failed
+  // stack: ptr
+  // if failed: exit(1)
+  // if succeeded: leave ptr on stack
+  if dup 0 < do
+    "Failed to allocate memory!\n" puts
+    1 exit
+  end
+end
+
+macro palloc_raw
+  // takes length of memory to be allocated in bytes
+  // returns pointer to the start
+  // void *addr, size_t length, int prot, int flags, int fd, off_t offset SYSCALL_NUMBER
+  0 swap
+  -1 swap 
+  MAP_PRIVATE MAP_ANONYMOUS or swap
+  PROT_READ PROT_WRITE or swap
+  NULL
+  SYS_mmap
+  syscall6
+  // stack is now: size, returncode/ptr
+  
+  exit_if_failed
+  cast(ptr)
+end
+macro palloc
+  // allocates a page, but no need to keep track of the size
+  // may allocate more in order to store the length
+  // pointer returned is still start of useable space (so can write to *ptr but shouldn't write to *(ptr-8))
+  8 + // need 8 bytes extra allocated for housekeeping
+  dup // keep size for later
+
+  palloc_raw
+
+  // stick size on the front, for housekeeping
+  swap over !64
+  // left with just the pointer
+  8 +
+end
+
+macro pfree_raw
+  // Takes pointer, size on stack
+  swap
+  SYS_munmap
+  syscall2
+  if dup 0 != do
+    "Error freeing: " puts print " not equal to 0\n" puts
+  else
+    drop
+    "Freed successfully\n" puts
+  end
+end
+
+macro pfree
+  // takes pointer of allocated memory
+  // size stored at ptr - 8
+  8 -
+  dup
+  @64
+  pfree_raw
+end
diff --git a/std/std.porth b/std/std.porth
index 41b24325..ec6b80ae 100644
--- a/std/std.porth
+++ b/std/std.porth
@@ -364,6 +364,12 @@ macro dec64
   dup ,64 1 - .64
 end
 
+macro abs
+  if dup 0 < do
+    0 over - swap drop
+  end
+end
+
 macro strlen
   dup
   while dup , 0 != do 1 + end