[JITLink] Switch from an atom-based model to a "blocks and symbols" model.

In the Atom model the symbols, content and relocations of a relocatable object
file are represented as a graph of atoms, where each Atom represents a
contiguous block of content with a single name (or no name at all if the
content is anonymous), and where edges between Atoms represent relocations.
If more than one symbol is associated with a contiguous block of content then
the content is broken into multiple atoms and layout constraints (represented by
edges) are introduced to ensure that the content remains effectively contiguous.
These layout constraints must be kept in mind when examining the content
associated with a symbol (it may be spread over multiple atoms) or when applying
certain relocation types (e.g. MachO subtractors).

This patch replaces the Atom model in JITLink with a blocks-and-symbols model.
The blocks-and-symbols model represents relocatable object files as bipartite
graphs, with one set of nodes representing contiguous content (Blocks) and
another representing named or anonymous locations (Symbols) within a Block.
Relocations are represented as edges from Blocks to Symbols. This scheme
removes layout constraints (simplifying handling of MachO alt-entry symbols,
and hopefully ELF sections at some point in the future) and simplifies some
relocation logic.

llvm-svn: 373689

1 files changed, 7 insertions, 10 deletions

diff --git a/llvm/lib/ExecutionEngine/JITLink/JITLinkMemoryManager.cpp b/llvm/lib/ExecutionEngine/JITLink/JITLinkMemoryManager.cpp
index 267307cfde0..ecc6793bbce 100644
--- a/llvm/lib/ExecutionEngine/JITLink/JITLinkMemoryManager.cpp
+++ b/llvm/lib/ExecutionEngine/JITLink/JITLinkMemoryManager.cpp
@@ -61,6 +61,10 @@ InProcessMemoryManager::allocate(const SegmentsRequestMap &Request) {
     AllocationMap SegBlocks;
   };
 
+  if (!isPowerOf2_64((uint64_t)sys::Process::getPageSizeEstimate()))
+    return make_error<StringError>("Page size is not a power of 2",
+                                   inconvertibleErrorCode());
+
   AllocationMap Blocks;
   const sys::Memory::ProtectionFlags ReadWrite =
       static_cast<sys::Memory::ProtectionFlags>(sys::Memory::MF_READ |
@@ -69,19 +73,12 @@ InProcessMemoryManager::allocate(const SegmentsRequestMap &Request) {
   for (auto &KV : Request) {
     auto &Seg = KV.second;
 
-    if (Seg.getContentAlignment() > sys::Process::getPageSizeEstimate())
+    if (Seg.getAlignment() > sys::Process::getPageSizeEstimate())
       return make_error<StringError>("Cannot request higher than page "
                                      "alignment",
                                      inconvertibleErrorCode());
 
-    if (sys::Process::getPageSizeEstimate() % Seg.getContentAlignment() != 0)
-      return make_error<StringError>("Page size is not a multiple of "
-                                     "alignment",
-                                     inconvertibleErrorCode());
-
-    uint64_t ZeroFillStart =
-        alignTo(Seg.getContentSize(), Seg.getZeroFillAlignment());
-    uint64_t SegmentSize = ZeroFillStart + Seg.getZeroFillSize();
+    uint64_t SegmentSize = Seg.getContentSize() + Seg.getZeroFillSize();
 
     std::error_code EC;
     auto SegMem =
@@ -91,7 +88,7 @@ InProcessMemoryManager::allocate(const SegmentsRequestMap &Request) {
       return errorCodeToError(EC);
 
     // Zero out the zero-fill memory.
-    memset(static_cast<char *>(SegMem.base()) + ZeroFillStart, 0,
+    memset(static_cast<char *>(SegMem.base()) + Seg.getContentSize(), 0,
            Seg.getZeroFillSize());
 
     // Record the block for this segment.