[ELF] Support INSERT [AFTER|BEFORE] for orphan sections

D43468+D44380 added INSERT [AFTER|BEFORE] for non-orphan sections. This patch
makes INSERT work for orphan sections as well.

`SECTIONS {...} INSERT [AFTER|BEFORE] .foo` does not set `hasSectionCommands`, so the result
will be similar to a regular link without a linker script. The differences when `hasSectionCommands` is set include:

* image base is different
* -z noseparate-code/-z noseparate-loadable-segments are unavailable
* some special symbols such as `_end _etext _edata` are not defined

The behavior is similar to GNU ld:
INSERT is not considered an external linker script.

This feature makes the section layout more flexible. It can be used to:

* Place .nv_fatbin before other readonly SHT_PROGBITS sections to mitigate relocation overflows.
* Disturb the layout to expose address sensitive application bugs.

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D74375

1 files changed, 19 insertions, 19 deletions

diff --git a/lld/ELF/ScriptParser.cpp b/lld/ELF/ScriptParser.cpp
index 635d281..8186420 100644
--- a/lld/ELF/ScriptParser.cpp
+++ b/lld/ELF/ScriptParser.cpp
@@ -523,13 +523,6 @@ std::vector<BaseCommand *> ScriptParser::readOverlay() {
 }
 
 void ScriptParser::readSections() {
-  script->hasSectionsCommand = true;
-
-  // -no-rosegment is used to avoid placing read only non-executable sections in
-  // their own segment. We do the same if SECTIONS command is present in linker
-  // script. See comment for computeFlags().
-  config->singleRoRx = true;
-
   expect("{");
   std::vector<BaseCommand *> v;
   while (!errorCount() && !consume("}")) {
@@ -548,22 +541,29 @@ void ScriptParser::readSections() {
     else
       v.push_back(readOutputSectionDescription(tok));
   }
+  script->sectionCommands.insert(script->sectionCommands.end(), v.begin(),
+                                 v.end());
 
-  if (!atEOF() && consume("INSERT")) {
-    std::vector<BaseCommand *> *dest = nullptr;
-    if (consume("AFTER"))
-      dest = &script->insertAfterCommands[next()];
-    else if (consume("BEFORE"))
-      dest = &script->insertBeforeCommands[next()];
-    else
-      setError("expected AFTER/BEFORE, but got '" + next() + "'");
-    if (dest)
-      dest->insert(dest->end(), v.begin(), v.end());
+  if (atEOF() || !consume("INSERT")) {
+    // --no-rosegment is used to avoid placing read only non-executable sections
+    // in their own segment. We do the same if SECTIONS command is present in
+    // linker script. See comment for computeFlags().
+    // TODO This rule will be dropped in the future.
+    config->singleRoRx = true;
+
+    script->hasSectionsCommand = true;
     return;
   }
 
-  script->sectionCommands.insert(script->sectionCommands.end(), v.begin(),
-                                 v.end());
+  bool isAfter = false;
+  if (consume("AFTER"))
+    isAfter = true;
+  else if (!consume("BEFORE"))
+    setError("expected AFTER/BEFORE, but got '" + next() + "'");
+  StringRef where = next();
+  for (BaseCommand *cmd : v)
+    if (auto *os = dyn_cast<OutputSection>(cmd))
+      script->insertCommands.push_back({os, isAfter, where});
 }
 
 void ScriptParser::readTarget() {