[lld-macho] Don't support relocations in cstring sections

We can technically handle them, but since they shouldn't come up in any
real-world programs (since ld64 dedups strings unconditionally), there's
no reason to support them.

It's a thoroughly untested code path too -- as evidenced by the fact
that the only test this change breaks is one that verifies that we
reject relocations when dedup'ing. There is no test that covers the case
where we handle relocations in cstring sections when dedup is disabled.

Reviewed By: #lld-macho, oontvoo, keith, thakis

Differential Revision: https://reviews.llvm.org/D141025

Author: int3

lld/MachO/InputFiles.cpp

@@ -343,23 +343,20 @@ void ObjFile::parseSections(ArrayRef<SectionHeader> sectionHeaders) {
     };
 
     if (sectionType(sec.flags) == S_CSTRING_LITERALS) {
-      if (sec.nreloc && config->dedupStrings)
-        fatal(toString(this) + " contains relocations in " + sec.segname + "," +
-              sec.sectname +
-              ", so LLD cannot deduplicate strings. Try re-running with "
-              "--no-deduplicate-strings.");
-
-      InputSection *isec = make<CStringInputSection>(
-          section, data, align,
-          /*dedupLiterals=*/name == section_names::objcMethname ||
-              config->dedupStrings);
+      if (sec.nreloc)
+        fatal(toString(this) + ": " + sec.segname + "," + sec.sectname +
+              " contains relocations, which is unsupported");
+      bool dedupLiterals =
+          name == section_names::objcMethname || config->dedupStrings;
+      InputSection *isec =
+          make<CStringInputSection>(section, data, align, dedupLiterals);
       // FIXME: parallelize this?
       cast<CStringInputSection>(isec)->splitIntoPieces();
       section.subsections.push_back({0, isec});
     } else if (isWordLiteralSection(sec.flags)) {
       if (sec.nreloc)
-        fatal(toString(this) + " contains unsupported relocations in " +
-              sec.segname + "," + sec.sectname);
+        fatal(toString(this) + ": " + sec.segname + "," + sec.sectname +
+              " contains relocations, which is unsupported");
       InputSection *isec = make<WordLiteralInputSection>(section, data, align);
       section.subsections.push_back({0, isec});
     } else if (auto recordSize = getRecordSize(segname, name)) {

lld/test/MachO/invalid/cstring-dedup.s

@@ -11,7 +11,7 @@
 # RUN: not %lld -dylib %t/relocs.o 2>&1 | FileCheck %s --check-prefix=RELOCS
 
 # TERM:   not-terminated.o:(__cstring+0x4): string is not null terminated
-# RELOCS: relocs.o contains relocations in __TEXT,__cstring, so LLD cannot deduplicate strings. Try re-running with --no-deduplicate-strings.
+# RELOCS: error: {{.*}}relocs.o: __TEXT,__cstring contains relocations, which is unsupported
 
 #--- not-terminated.s
 .cstring