[ELF] Allow `ASSERT` in output section descriptions

[meadori]

Summary

GNU LD allows ASSERT commands to be in output section descriptions.
Note that LD also mandates that ASSERT commands in this context must
end with a semicolon.

[ruiu]

ELF/LinkerScript.cpp

474

Don't you need to pass Dot instead of 0, do you?

1421–1428

Since you added {}, please add braces to all if's here.

1427–1428

Remove this comment as it is obvious.

[meadori]

ELF/LinkerScript.cpp

474

Yup, you are right. Will fix.

1421–1428

Will do.

1427–1428

Will do.

[meadori]

Address review feedback.

[ruiu]

LGTM. Thanks!

test/ELF/linkerscript/assert.s

33–38

Can you write this in one line? Look at other tests in this file.

[meadori]

test/ELF/linkerscript/assert.s

33–38

Sure. I noticed the recent changes to the tests in this file and changed the test following this one to be on one line. I left this one alone b/c it was a bit longer. Is it OK to exceed 80 columns?

[ruiu]

test/ELF/linkerscript/assert.s

33–38

I'd make it one line even if it exceeds 80 columns a bit. Because otherwise an error message for this test would be really hard to read. It becomes something like this as it contains lots of spaces.

error: foo1.o:1: SECTIONS { <lots of spaces> .foo { <lots of spaces> ASSERT(...) <lots of spaces> ...
error: foo1.o:1:                                   <lots of spaces> ^ error here

That's why I changed other tests.

[meadori]

Committed. Thanks for the review Rui.

ELF/LinkerScript.cpp

template <class ELFT> void LinkerScript<ELFT>::process(BaseCommand &Base) {
   // Handle BYTE(), SHORT(), LONG(), or QUAD().
   if (auto *DataCmd = dyn_cast<BytesDataCommand>(&Base)) {
     DataCmd->Offset = Dot - CurOutSec->Addr;
     Dot += DataCmd->Size;
     CurOutSec->Size = Dot - CurOutSec->Addr;
     return;
   }
 
+  if (auto *AssertCmd = dyn_cast<AssertCommand>(&Base)) {
+    AssertCmd->Expression(Dot);
+    return;
+  }
+
   // It handles single input section description command,
   // calculates and assigns the offsets for each section and also
   // updates the output section size.
   auto &ICmd = cast<InputSectionDescription>(Base);
   for (InputSectionData *ID : ICmd.Sections) {
     auto *IB = static_cast<InputSectionBase<ELFT> *>(ID);
     switchTo(IB->OutSec);
     if (auto *I = dyn_cast<InputSection<ELFT>>(IB))
ScriptParser::readOutputSectionDescription(StringRef OutSec) {
   if (consume("ONLY_IF_RO"))
     Cmd->Constraint = ConstraintKind::ReadOnly;
   if (consume("ONLY_IF_RW"))
     Cmd->Constraint = ConstraintKind::ReadWrite;
   expect("{");
 
   while (!Error && !consume("}")) {
     StringRef Tok = next();
-    if (SymbolAssignment *Assignment = readProvideOrAssignment(Tok))
+    if (SymbolAssignment *Assignment = readProvideOrAssignment(Tok)) {
       Cmd->Commands.emplace_back(Assignment);
-    else if (BytesDataCommand *Data = readBytesDataCommand(Tok))
+    } else if (BytesDataCommand *Data = readBytesDataCommand(Tok)) {
       Cmd->Commands.emplace_back(Data);
-    else if (Tok == "FILL")
+    } else if (Tok == "ASSERT") {
+      Cmd->Commands.emplace_back(new AssertCommand(readAssert()));
+      expect(";");
+    } else if (Tok == "FILL") {
       Cmd->Filler = readFill();
-    else if (Tok == "SORT")
+    } else if (Tok == "SORT") {
       readSort();
-    else if (peek() == "(")
+    } else if (peek() == "(") {
       Cmd->Commands.emplace_back(readInputSectionDescription(Tok));
-    else
+    } else {
       setError("unknown command " + Tok);
     }
+  }
   Cmd->Phdrs = readOutputSectionPhdrs();
 
   if (consume("="))
     Cmd->Filler = readOutputSectionFiller(next());
   else if (peek().startswith("="))
     Cmd->Filler = readOutputSectionFiller(next().drop_front());
 
   return Cmd;

test/ELF/linkerscript/assert.s

 # RUN: llvm-readobj %t5 > /dev/null
 
 ## Even without SECTIONS block we still use section names
 ## in expressions
 # RUN: echo "ASSERT(SIZEOF(.foo) == 8, fail);" > %t5.script
 # RUN: ld.lld -shared -o %t5 --script %t5.script %t1.o
 # RUN: llvm-readobj %t5 > /dev/null
 
+## Test assertions inside of output section decriptions.
+# RUN: echo "SECTIONS {                         \
+# RUN:   .foo : {                               \
+# RUN:     *(.foo)                              \
+# RUN:     ASSERT(SIZEOF(.foo) == 8, \"true\"); \
+# RUN:   }                                      \
+# RUN: }" > %t6.script
+# RUN: ld.lld -shared -o %t6 --script %t6.script %t1.o
+# RUN: llvm-readobj %t6 > /dev/null
+
+# RUN: echo "SECTIONS { .foo : { ASSERT(1, \"true\") } }" > %t7.script
+# RUN: not ld.lld -shared -o %t7 --script %t7.script %t1.o > %t.log 2>&1
+# RUN: FileCheck %s -check-prefix=CHECK-SEMI < %t.log
+# CHECK-SEMI: error: {{.*}}.script:1: ; expected, but got }
+
 .section .foo, "a"
  .quad 0