[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, 9 insertions, 4 deletions

diff --git a/lld/ELF/LinkerScript.h b/lld/ELF/LinkerScript.h
index f020552..848e3e4 100644
--- a/lld/ELF/LinkerScript.h
+++ b/lld/ELF/LinkerScript.h
@@ -208,6 +208,12 @@ struct ByteCommand : BaseCommand {
   unsigned size;
 };
 
+struct InsertCommand {
+  OutputSection *os;
+  bool isAfter;
+  StringRef where;
+};
+
 struct PhdrsCommand {
   StringRef name;
   unsigned type = llvm::ELF::PT_NULL;
@@ -311,10 +317,9 @@ public:
   // A list of symbols referenced by the script.
   std::vector<llvm::StringRef> referencedSymbols;
 
-  // Used to implement INSERT [AFTER|BEFORE]. Contains commands that need
-  // to be inserted into SECTIONS commands list.
-  llvm::DenseMap<StringRef, std::vector<BaseCommand *>> insertAfterCommands;
-  llvm::DenseMap<StringRef, std::vector<BaseCommand *>> insertBeforeCommands;
+  // Used to implement INSERT [AFTER|BEFORE]. Contains output sections that need
+  // to be reordered.
+  std::vector<InsertCommand> insertCommands;
 };
 
 extern LinkerScript *script;