[ELF] - Report an error if empty sections are referenced in LOADADDR/ADDR commands.

[grimar]

Summary

If script references empty sections in LOADADDR/ADDR commands:

.empty  : { *(.empty ) }
.text   : AT(LOADADDR (.empty) + SIZEOF (.empty)) { *(.text) }

then an empty section will be removed and LOADADDR/ADDR will evaluate to null.
It is not that user may expect from using of the generic script, what is a common case.

This is an alternative version of D54621, in this patch, I just report an error in this case,
so that we do not emit broken output silently.

[peter.smith]

I personally would prefer D54621 but I think this is better than producing incorrect output.

test/ELF/linkerscript/empty-sections-expressions.test

5

The FileCheck part of the command looks to have been corrupted somehow. I'm seeing ileCheck %s ff.

[grimar]

• Fixed test case.

test/ELF/linkerscript/empty-sections-expressions.test

5

Oh. And the test still passed. Fixed, thanks!

[grimar]

In D55118#1314445, @peter.smith wrote:

I personally would prefer D54621 but I think this is better than producing incorrect output.

I probably also see no solid reason not to go with D54621 instead.

[grimar]

D54621 was landed instead.

ELF/ScriptParser.cpp

StringRef ScriptParser::readParenLiteral() {
   InExpr = false;
   StringRef Tok = next();
   InExpr = Orig;
   expect(")");
   return Tok;
 }
 
 static void checkIfExists(OutputSection *Cmd, StringRef Location) {
-  if (Cmd->Location.empty() && Script->ErrorOnMissingSection)
+  if (!Script->ErrorOnMissingSection)
+    return;
+
+  if (Cmd->Location.empty())
     error(Location + ": undefined section " + Cmd->Name);
+  else if (!Cmd->Live)
+    error(Cmd->Location + ": reference to removed section '" + Cmd->Name +
+          "' not allowed");
 }
 
 Expr ScriptParser::readPrimary() {
   if (peek() == "(")
     return readParenExpr();
 
   if (consume("~")) {
     Expr E = readPrimary();

test/ELF/linkerscript/empty-sections-expressions.test

+# REQUIRES: x86
+# RUN: echo ".text; nop; .data; .byte 0" \
+# RUN:   | llvm-mc -filetype=obj -triple=x86_64-pc-linux - -o %t.o
+# RUN: not ld.lld -o %t --script %s %t.o 2>&1 | FileCheck %s
+
+# CHECK: error: {{.*}}.test:10: reference to removed section '.empty' not allowed
+
+SECTIONS {
+ . = 0x00080000;
+ .empty  : { *(.empty ) }
+ .text   : AT(LOADADDR (.empty)) { *(.text) }
+ .data   : AT(ADDR (.empty)) { *(.data) }
+}