reorganization, cross compiler

1 files changed, 32 insertions, 0 deletions

diff --git a/documentation/euler/heap.txt b/documentation/euler/heap.txt
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+this file documents dynamic memory allocation and deallocation in userspace.
+the unused areas of a process's usable mapped memory are divided into "chunks"
+with a start and a length, satisfying the following properties:
+  a) the length of a chunk is a positive power of 2
+  b) the start of a chunk is a multiple of its length
+  c) let s be a power of 2 and k be an integer. there are never two chunks with
+     length s and starts s * (2 * k) and s * (2 * k + 1). if ever an operation
+     would result in two such chunks, they are combined into one chunk with
+     length 2 * s and start 2 * s * k.
+
+a "chunk info page" is divided into 512 64-bit integers describing up to 255
+chunks and a pointer to another chunk info page. for each n from 0 to 254:
+  if the (2 * n)'th integer (where the first integer is the 0th one) is 0:
+    the (2 * n + 1)'th integer is unused.
+  if the (2 * n)'th integer is not 0:
+    the (2 * n)'th integer describes the length of a chunk
+    the (2 * n + 1)'th integer describes the start of the same chunk
+the 510th integer is a pointer to the next chunk info page, and the 511th
+integer is never used.
+
+when a program calls new or malloc with needed size s, we find a free chunk of
+length at least s + 8. we then remove that chunk from the list of free chunks,
+and add back in whatever is left after the first s + 8 bytes, if anything.
+in the first 8 bytes of the original chunk, we store the value s + 8. the
+remainder of the orginal chunk is returned to the program.
+
+during that process, if there isn't a chunk with the needed size, one or more
+new pages are requested from the kernel to create such a chunk.
+
+when a program calls delete or free with pointer ptr, we read the integer in
+the 8 bytes starting at ptr - 8 into a variable s. we then add the region
+starting at ptr - 8 with length s to the free memory.