[LLD][ELF] Allow memory region in OVERLAY

lld/ELF/LinkerScript.cpp

@@ -182,7 +182,18 @@ void LinkerScript::expandMemoryRegions(uint64_t size) {
 
 void LinkerScript::expandOutputSection(uint64_t size) {
   state->outSec->size += size;
-  expandMemoryRegions(size);
+  size_t regionSize = size;
+  if (state->outSec->inOverlay) {
+    // Expand the overlay if necessary, and expand the region by the
+    // corresponding amount.
+    if (state->outSec->size > state->overlaySize) {
+      regionSize = state->outSec->size - state->overlaySize;
+      state->overlaySize = state->outSec->size;
+    } else {
+      regionSize = 0;
+    }
+  }
+  expandMemoryRegions(regionSize);
 }
 
 void LinkerScript::setDot(Expr e, const Twine &loc, bool inSec) {
@@ -1218,6 +1229,8 @@ bool LinkerScript::assignOffsets(OutputSection *sec) {
   // We can call this method multiple times during the creation of
   // thunks and want to start over calculation each time.
   sec->size = 0;
+  if (sec->firstInOverlay)
+    state->overlaySize = 0;
 
   // We visited SectionsCommands from processSectionCommands to
   // layout sections. Now, we visit SectionsCommands again to fix

lld/ELF/LinkerScript.h

@@ -311,6 +311,7 @@ class LinkerScript final {
     MemoryRegion *lmaRegion = nullptr;
     uint64_t lmaOffset = 0;
     uint64_t tbssAddr = 0;
+    uint64_t overlaySize;
   };
 
   Ctx &ctx;

lld/ELF/OutputSections.h

@@ -102,6 +102,7 @@ class OutputSection final : public SectionBase {
   bool expressionsUseSymbols = false;
   bool usedInExpression = false;
   bool inOverlay = false;
+  bool firstInOverlay = false;
 
   // Tracks whether the section has ever had an input section added to it, even
   // if the section was later removed (e.g. because it is a synthetic section

lld/ELF/ScriptParser.cpp

@@ -561,37 +561,40 @@ void ScriptParser::readSearchDir() {
 // https://sourceware.org/binutils/docs/ld/Overlay-Description.html#Overlay-Description
 SmallVector<SectionCommand *, 0> ScriptParser::readOverlay() {
   Expr addrExpr;
-  if (consume(":")) {
-    addrExpr = [s = ctx.script] { return s->getDot(); };
-  } else {
+  if (!consume(":")) {
     addrExpr = readExpr();
     expect(":");
   }
-  // When AT is omitted, LMA should equal VMA. script->getDot() when evaluating
-  // lmaExpr will ensure this, even if the start address is specified.
-  Expr lmaExpr = consume("AT") ? readParenExpr()
-                               : [s = ctx.script] { return s->getDot(); };
+  Expr lmaExpr = consume("AT") ? readParenExpr() : Expr{};
   expect("{");
 
   SmallVector<SectionCommand *, 0> v;
   OutputSection *prev = nullptr;
   while (!errCount(ctx) && !consume("}")) {
     // VA is the same for all sections. The LMAs are consecutive in memory
-    // starting from the base load address specified.
+    // starting from the base load address.
     OutputDesc *osd = readOverlaySectionDescription();
     osd->osec.addrExpr = addrExpr;
     if (prev) {
       osd->osec.lmaExpr = [=] { return prev->getLMA() + prev->size; };
     } else {
       osd->osec.lmaExpr = lmaExpr;
-      // Use first section address for subsequent sections as initial addrExpr
-      // can be DOT. Ensure the first section, even if empty, is not discarded.
+      // Use first section address for subsequent sections. Ensure the first
+      // section, even if empty, is not discarded.
       osd->osec.usedInExpression = true;
       addrExpr = [=]() -> ExprValue { return {&osd->osec, false, 0, ""}; };
     }
     v.push_back(osd);
     prev = &osd->osec;
   }
+  if (!v.empty())
+    static_cast<OutputDesc *>(v.front())->osec.firstInOverlay = true;
+  if (consume(">")) {
+    StringRef regionName = readName();
+    for (SectionCommand *od : v)
+      static_cast<OutputDesc *>(od)->osec.memoryRegionName =
+          std::string(regionName);
+  }
 
   // According to the specification, at the end of the overlay, the location
   // counter should be equal to the overlay base address plus size of the

lld/test/ELF/linkerscript/overlay.test

@@ -41,6 +41,23 @@
 # ERR2-NEXT:>>>     .out.aaa { *(.aaa) } > AX AT>FLASH
 # ERR2-NEXT:>>>                            ^
 
+# RUN: ld.lld a.o -T region.t -o region
+# RUN: llvm-readelf --sections -l region | FileCheck --check-prefix=REGION %s
+
+# REGION:      Name       Type     Address          Off    Size
+# REGION:      .big1      PROGBITS 0000000000001000 001000 000008
+# REGION-NEXT: .small1    PROGBITS 0000000000001000 002000 000004
+# REGION:      .big2      PROGBITS 0000000000001008 002008 000008
+# REGION-NEXT: .small2    PROGBITS 0000000000001008 003008 000004
+# REGION-NEXT: .text      PROGBITS 0000000000001010 003010 000001
+
+# REGION:      Program Headers:
+# REGION:      Type Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
+# REGION-NEXT: LOAD 0x001000 0x0000000000001000 0x0000000000001000 0x000008 0x000008 R   0x1000
+# REGION-NEXT: LOAD 0x002000 0x0000000000001000 0x0000000000001008 0x000010 0x000010 R   0x1000
+# REGION-NEXT: LOAD 0x003008 0x0000000000001008 0x0000000000001018 0x000004 0x000004 R   0x1000
+# REGION-NEXT: LOAD 0x003010 0x0000000000001010 0x0000000000001020 0x000001 0x000001 R E 0x1000
+
 #--- a.s
 .globl _start
 _start:
@@ -76,6 +93,22 @@ SECTIONS {
   .text : { *(.text) }
 }
 
+#--- region.t
+MEMORY { region : ORIGIN = 0x1000, LENGTH = 0x1000 }
+SECTIONS {
+## Memory region instead of explicit address.
+  OVERLAY : {
+    .big1 { *(.big1) }
+    .small1 { *(.small1) }
+  } >region
+  OVERLAY : {
+    .big2 { *(.big2) }
+    .small2 { *(.small2) }
+  } >region
+  .text : { *(.text) } >region
+  /DISCARD/ : { *(.big* .small*) }
+}
+
 #--- err1.t
 SECTIONS {
   OVERLAY 0x1000 : AT ( 0x2000 ) {