[PATCH] D43944: [ELF] - Refactoring of the elf/program headers allocation code.

[George Rimar via Phabricator via llvm-commits]

grimar created this revision.
grimar added reviewers: ruiu, espindola.
Herald added subscribers: arichardson, emaste.

I suggest this refactoring for code that allocates
elf/program headers.

I believe it is a bit easier to read.


https://reviews.llvm.org/D43944

Files:
  ELF/LinkerScript.cpp


Index: ELF/LinkerScript.cpp
===================================================================
--- ELF/LinkerScript.cpp
+++ ELF/LinkerScript.cpp
@@ -897,13 +897,27 @@
   return nullptr;
 }
 
-static uint64_t computeBase(uint64_t Min, bool AllocateHeaders) {
+static bool hasExplicitHeaders(ArrayRef<PhdrsCommand> Phdrs) {
+  return llvm::any_of(Phdrs, [](const PhdrsCommand &Cmd) {
+    return Cmd.HasPhdrs || Cmd.HasFilehdr;
+  });
+}
+
+static Optional<uint64_t> getHeadersVA(uint64_t MinVA, uint64_t HeaderSize,
+                                       ArrayRef<PhdrsCommand> Phdrs) {
+  // Unable to allocate headers when their size is greater than minimal VA.
+  if (HeaderSize > MinVA)
+    return None;
+
   // If there is no SECTIONS or if the linkerscript is explicit about program
   // headers, do our best to allocate them.
-  if (!Script->HasSectionsCommand || AllocateHeaders)
-    return 0;
+  if (!Script->HasSectionsCommand || hasExplicitHeaders(Phdrs))
+    return alignDown(MinVA - HeaderSize, Config->MaxPageSize);
+
   // Otherwise only allocate program headers if that would not add a page.
-  return alignDown(Min, Config->MaxPageSize);
+  if (HeaderSize <= MinVA - alignDown(MinVA, Config->MaxPageSize))
+    return alignDown(MinVA - HeaderSize, Config->MaxPageSize);
+  return None;
 }
 
 // Try to find an address for the file and program headers output sections,
@@ -927,24 +941,19 @@
       Phdrs, [](const PhdrEntry *E) { return E->p_type == PT_LOAD; });
   if (It == Phdrs.end())
     return;
-  PhdrEntry *FirstPTLoad = *It;
 
-  bool HasExplicitHeaders =
-      llvm::any_of(PhdrsCommands, [](const PhdrsCommand &Cmd) {
-        return Cmd.HasPhdrs || Cmd.HasFilehdr;
-      });
-  uint64_t HeaderSize = getHeaderSize();
-  if (HeaderSize <= Min - computeBase(Min, HasExplicitHeaders)) {
-    Min = alignDown(Min - HeaderSize, Config->MaxPageSize);
-    Out::ElfHeader->Addr = Min;
-    Out::ProgramHeaders->Addr = Min + Out::ElfHeader->Size;
+  if (Optional<uint64_t> VA =
+          getHeadersVA(Min, getHeaderSize(), PhdrsCommands)) {
+    Out::ElfHeader->Addr = *VA;
+    Out::ProgramHeaders->Addr = *VA + Out::ElfHeader->Size;
     return;
   }
 
   // Error if we were explicitly asked to allocate headers.
-  if (HasExplicitHeaders)
+  if (hasExplicitHeaders(PhdrsCommands))
     error("could not allocate headers");
 
+  PhdrEntry *FirstPTLoad = *It;
   Out::ElfHeader->PtLoad = nullptr;
   Out::ProgramHeaders->PtLoad = nullptr;
   FirstPTLoad->FirstSec = findFirstSection(FirstPTLoad);


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