[lld] [LLD][ELF] Support OVERLAY NOCROSSREFS (PR #133807)

[Daniel Thornburgh via llvm-commits]

https://github.com/mysterymath created https://github.com/llvm/llvm-project/pull/133807

This allows NOCROSSREFS to be specified in OVERLAY linker script descriptions. This is a particularly useful part of the OVERLAY syntax, since it's very rarely possible for one overlay section to sensibly reference another.

Closes #128790

>From b067b9027db2f5a1f364fda1e60888d312775ce9 Mon Sep 17 00:00:00 2001
From: Daniel Thornburgh <mysterymath at gmail.com>
Date: Mon, 31 Mar 2025 10:47:43 -0700
Subject: [PATCH] [LLD][ELF] Support OVERLAY NOCROSSREFS

This allows NOCROSSREFS to be specified in OVERLAY linker script
descriptions. This is a particularly useful part of the OVERLAY syntax,
since it's very rarely possible for one overlay section to sensibly
reference another.

Closes #128790
---
 lld/ELF/ScriptParser.cpp                   | 19 +++++++++++++++++--
 lld/docs/ReleaseNotes.rst                  |  3 +++
 lld/test/ELF/linkerscript/nocrossrefs.test | 15 +++++++++++++++
 lld/test/ELF/linkerscript/overlay.test     | 11 +++++++++++
 4 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/lld/ELF/ScriptParser.cpp b/lld/ELF/ScriptParser.cpp
index 4345b7bac1173..95e1d24042644 100644
--- a/lld/ELF/ScriptParser.cpp
+++ b/lld/ELF/ScriptParser.cpp
@@ -565,8 +565,17 @@ SmallVector<SectionCommand *, 0> ScriptParser::readOverlay() {
     addrExpr = readExpr();
     expect(":");
   }
-  Expr lmaExpr = consume("AT") ? readParenExpr() : Expr{};
-  expect("{");
+
+  Expr lmaExpr;
+  bool noCrossRefs = false;
+  while (auto tok = till("{")) {
+    if (tok == "AT")
+      lmaExpr = readParenExpr();
+    else if (tok == "NOCROSSREFS")
+      noCrossRefs = true;
+    else
+      setError("{ expected, but got " + tok);
+  }
 
   SmallVector<SectionCommand *, 0> v;
   OutputSection *prev = nullptr;
@@ -595,6 +604,12 @@ SmallVector<SectionCommand *, 0> ScriptParser::readOverlay() {
       static_cast<OutputDesc *>(od)->osec.memoryRegionName =
           std::string(regionName);
   }
+  if (noCrossRefs) {
+    NoCrossRefCommand cmd;
+    for (SectionCommand *od : v)
+      cmd.outputSections.push_back(static_cast<OutputDesc *>(od)->osec.name);
+    ctx.script->noCrossRefs.push_back(std::move(cmd));
+  }
 
   // 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
diff --git a/lld/docs/ReleaseNotes.rst b/lld/docs/ReleaseNotes.rst
index 43ed6fa73589b..2b7b7fe52ea12 100644
--- a/lld/docs/ReleaseNotes.rst
+++ b/lld/docs/ReleaseNotes.rst
@@ -39,6 +39,9 @@ ELF Improvements
   items that kept it live during garbage collection. This is inspired by the
   Mach-O LLD feature of the same name.
 
+* Linker script ``OVERLAY`` descriptions now support virtual memory regions
+  (e.g. ``>region``) and ``NOCROSSREFS``.
+
 Breaking changes
 ----------------
 
diff --git a/lld/test/ELF/linkerscript/nocrossrefs.test b/lld/test/ELF/linkerscript/nocrossrefs.test
index 5eb56190fe63b..de0f1d0300b00 100644
--- a/lld/test/ELF/linkerscript/nocrossrefs.test
+++ b/lld/test/ELF/linkerscript/nocrossrefs.test
@@ -28,6 +28,10 @@
 # RUN: not ld.lld a.o data.o -T 3.t 2>&1 | FileCheck %s --check-prefix=CHECK3 --implicit-check-not=error:
 # CHECK3:      error: a.o:(.nonalloc+0x0): prohibited cross reference from '.nonalloc' to '.text' in '.text'
 
+# RUN: not ld.lld a.o data.o -T overlay.t 2>&1 | FileCheck %s --check-prefix=OVERLAY --implicit-check-not=error:
+# OVERLAY: error: a.o:(.text.start+0x11): prohibited cross reference from '.text' to 'data' in '.data'
+# OVERLAY-NEXT: error: a.o:(.text.start+0x17): prohibited cross reference from '.text' to 'str1' in '.rodata'
+
 #--- 0.t
 ## Some cases that do not cause errors.
 abs = 42;
@@ -50,6 +54,17 @@ NOCROSSREFS(.text .text1 .text2 .data .rodata .data .nonalloc)
 abs = 42;
 NOCROSSREFS_TO(.text .text .text1 .text2 .data .nonalloc)
 
+#--- overlay.t
+abs = 42;
+_edata = 43;
+SECTIONS {
+  OVERLAY : NOCROSSREFS {
+    .text { *(.text*) }
+    .data { *(.data*) }
+    .rodata { *(.rodata*) }
+  }
+}
+
 #--- err1.t
 NOCROSSREFS )
 
diff --git a/lld/test/ELF/linkerscript/overlay.test b/lld/test/ELF/linkerscript/overlay.test
index e230134ad5541..7bc98b5206a04 100644
--- a/lld/test/ELF/linkerscript/overlay.test
+++ b/lld/test/ELF/linkerscript/overlay.test
@@ -133,3 +133,14 @@ SECTIONS {
 # RUN: not ld.lld a.o -T unclosed.lds 2>&1 | FileCheck %s --check-prefix=UNCLOSED
 # UNCLOSED:     error: unclosed.lds:2: unexpected EOF
 # UNCLOSED-NOT: {{.}}
+
+#--- invalid-before-brace.lds
+SECTIONS {
+  OVERLAY 0x1000 : INVALID {
+  }
+}
+
+# RUN: not ld.lld a.o -T invalid-before-brace.lds 2>&1 | FileCheck %s --check-prefix=INVALID-BEFORE-BRACE --strict-whitespace
+# INVALID-BEFORE-BRACE:{{.*}}error: invalid-before-brace.lds:2: { expected, but got INVALID
+# INVALID-BEFORE-BRACE-NEXT:>>>   OVERLAY 0x1000 : INVALID {
+# INVALID-BEFORE-BRACE-NEXT:>>>                    ^