[ELF] Do not try to assign a memory region to a non-allocatable section

[ikudrin]

Summary

Non-allocatable sections are not part of the memory image of the program, so there is no need to find memory regions for them either matching properties or handling explicit assignments. The early test and return help to simplify LinkerScript::findMemoryRegion() a bit.

[MaskRay]

lld/test/ELF/linkerscript/memory-nonalloc.test

11

-o /dev/null --fatal-warnings

lld/ELF/LinkerScript.cpp

 
 // This function searches for a memory region to place the given output
 // section in. If found, a pointer to the appropriate memory region is
 // returned in the first member of the pair. Otherwise, a nullptr is returned.
 // The second member of the pair is a hint that should be passed to the
 // subsequent call of this method.
 std::pair<MemoryRegion *, MemoryRegion *>
 LinkerScript::findMemoryRegion(OutputSection *sec, MemoryRegion *hint) {
+  // Non-allocatable sections are not part of the process image.
+  if (!(sec->flags & SHF_ALLOC)) {
+    if (!sec->memoryRegionName.empty())
+      warn("ignoring memory region assignment for non-allocatable section '" +
+           sec->name + "'");
+    return {nullptr, nullptr};
+  }
+
   // If a memory region name was specified in the output section command,
   // then try to find that region first.
   if (!sec->memoryRegionName.empty()) {
     if (MemoryRegion *m = memoryRegions.lookup(sec->memoryRegionName))
       return {m, m};
     error("memory region '" + sec->memoryRegionName + "' not declared");
     return {nullptr, nullptr};
   }
 
   // If at least one memory region is defined, all sections must
   // belong to some memory region. Otherwise, we don't need to do
   // anything for memory regions.
   if (memoryRegions.empty())
     return {nullptr, nullptr};
 
-  // An allocatable orphan section should continue the previous memory region.
-  if (sec->sectionIndex == UINT32_MAX && (sec->flags & SHF_ALLOC) && hint)
+  // An orphan section should continue the previous memory region.
+  if (sec->sectionIndex == UINT32_MAX && hint)
     return {hint, hint};
 
   // See if a region can be found by matching section flags.
   for (auto &pair : memoryRegions) {
     MemoryRegion *m = pair.second;
     if ((m->flags & sec->flags) && (m->negFlags & sec->flags) == 0)
       return {m, nullptr};
   }
 
   // Otherwise, no suitable region was found.
-  if (sec->flags & SHF_ALLOC)
-    error("no memory region specified for section '" + sec->name + "'");
   return {nullptr, nullptr};
 }
 
 static OutputSection *findFirstSection(PhdrEntry *load) {
   for (OutputSection *sec : outputSections)
     if (sec->ptLoad == load)
       return sec;
   return nullptr;

lld/test/ELF/linkerscript/memory-nonalloc.test

+REQUIRES: x86
+
+RUN: split-file %s %ts
+RUN: llvm-mc -filetype=obj -triple=x86_64 %ts/s -o %t.o
+
+## Check that a non-allocatable section is not assigned to a memory region by
+## matching the section/region properties. Previously, that could lead to an
+## "error: section '.nonalloc' will not fit in region 'RAM'".
+
+RUN: ld.lld %t.o -T %ts/t --fatal-warnings -o /dev/null
+
+## Check that an explicit assignment is ignored for a non-allocatable section.
+## Previously, that also could lead to the same error.
+
+RUN: ld.lld %t.o -T %ts/t2 -o /dev/null 2>&1 | FileCheck %s --check-prefix=WARN
+
+WARN: warning: ignoring memory region assignment for non-allocatable section '.nonalloc'
+
+#--- s
+  .global _start
+_start:
+
+  ## Note: a "writable" section is used because lld does not fully support
+  ## memory region attribute "r" at the moment.
+  .section .nonalloc,"w"
+  .zero 0x1000
+
+#--- t
+MEMORY
+{
+  RAM (rwx) : ORIGIN = 0x8000, LENGTH = 0x100
+}
+
+SECTIONS
+{
+  .nonalloc : { *(.nonalloc) }
+}
+
+#--- t2
+MEMORY
+{
+  RAM (rwx) : ORIGIN = 0x8000, LENGTH = 0x100
+}
+
+SECTIONS
+{
+  .nonalloc : { *(.nonalloc) } > RAM
+}