[ELF] - Report error if removed empty output section declaration used undefined symbols.

This is for fixing PR36297.

Issue itself is that if we have SECTIONS { .bar (a+b) : { *(.stub) } };
script and no section .stub, when LLD will remove .bar, but
produce output with undefined symbols a and b.

Differential revision: https://reviews.llvm.org/D43069

llvm-svn: 325875

1 files changed, 7 insertions, 0 deletions

diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index e9ea4f84587..0426c503df0 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -767,6 +767,13 @@ void LinkerScript::removeEmptyCommands() {
 }
 
 static bool isAllSectionDescription(const OutputSection &Cmd) {
+  // We do not want to remove sections that have custom address or align
+  // expressions set even if them are empty. We keep them because we
+  // want to be sure that any expressions can be evaluated and report
+  // an error otherwise.
+  if (Cmd.AddrExpr || Cmd.AlignExpr || Cmd.LMAExpr)
+    return false;
+
   for (BaseCommand *Base : Cmd.SectionCommands)
     if (!isa<InputSectionDescription>(*Base))
       return false;