From 39add80ac5626817e840dfa60cd184277004da86 Mon Sep 17 00:00:00 2001
From: Eric Christopher <echristo@gmail.com>
Date: Mon, 25 Jun 2018 23:53:54 +0000
Subject: [PATCH] Add a warning if someone attempts to add extra section flags
 to sections with well defined semantics like .rodata.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335558 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/MC/MCParser/ELFAsmParser.cpp  | 49 ++++++++++++++++++++++++++-------------
 test/MC/ELF/extra-section-flags.s | 10 ++++++++
 2 files changed, 43 insertions(+), 16 deletions(-)
 create mode 100644 test/MC/ELF/extra-section-flags.s

diff --git a/lib/MC/MCParser/ELFAsmParser.cpp b/lib/MC/MCParser/ELFAsmParser.cpp
index dc5b0e0d031..93513a2c415 100644
--- a/lib/MC/MCParser/ELFAsmParser.cpp
+++ b/lib/MC/MCParser/ELFAsmParser.cpp
@@ -481,6 +481,31 @@ static bool hasPrefix(StringRef SectionName, StringRef Prefix) {
   return SectionName.startswith(Prefix) || SectionName == Prefix.drop_back();
 }
 
+// Return a set of section flags based on the section name that can then
+// be augmented later, otherwise return 0 if we don't have any reasonable
+// defaults.
+static unsigned defaultSectionFlags(StringRef SectionName) {
+
+  if (hasPrefix(SectionName, ".rodata.") || SectionName == ".rodata1")
+    return ELF::SHF_ALLOC;
+
+  if (SectionName == ".fini" || SectionName == ".init" ||
+      hasPrefix(SectionName, ".text."))
+    return ELF::SHF_ALLOC | ELF::SHF_EXECINSTR;
+
+  if (hasPrefix(SectionName, ".data.") || SectionName == ".data1" ||
+      hasPrefix(SectionName, ".bss.") ||
+      hasPrefix(SectionName, ".init_array.") ||
+      hasPrefix(SectionName, ".fini_array.") ||
+      hasPrefix(SectionName, ".preinit_array."))
+    return ELF::SHF_ALLOC | ELF::SHF_WRITE;
+
+  if (hasPrefix(SectionName, ".tdata.") || hasPrefix(SectionName, ".tbss."))
+    return ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_TLS;
+
+  return 0;
+}
+
 bool ELFAsmParser::ParseSectionArguments(bool IsPush, SMLoc loc) {
   StringRef SectionName;
 
@@ -490,27 +515,13 @@ bool ELFAsmParser::ParseSectionArguments(bool IsPush, SMLoc loc) {
   StringRef TypeName;
   int64_t Size = 0;
   StringRef GroupName;
-  unsigned Flags = 0;
   const MCExpr *Subsection = nullptr;
   bool UseLastGroup = false;
   MCSymbolELF *Associated = nullptr;
   int64_t UniqueID = ~0;
 
-  // Set the defaults first.
-  if (hasPrefix(SectionName, ".rodata.") || SectionName == ".rodata1")
-    Flags |= ELF::SHF_ALLOC;
-  else if (SectionName == ".fini" || SectionName == ".init" ||
-           hasPrefix(SectionName, ".text."))
-    Flags |= ELF::SHF_ALLOC | ELF::SHF_EXECINSTR;
-  else if (hasPrefix(SectionName, ".data.") || SectionName == ".data1" ||
-           hasPrefix(SectionName, ".bss.") ||
-           hasPrefix(SectionName, ".init_array.") ||
-           hasPrefix(SectionName, ".fini_array.") ||
-           hasPrefix(SectionName, ".preinit_array."))
-    Flags |= ELF::SHF_ALLOC | ELF::SHF_WRITE;
-  else if (hasPrefix(SectionName, ".tdata.") ||
-           hasPrefix(SectionName, ".tbss."))
-    Flags |= ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_TLS;
+  // Set the default section flags first in case no others are given.
+  unsigned Flags = defaultSectionFlags(SectionName);
 
   if (getLexer().is(AsmToken::Comma)) {
     Lex();
@@ -538,6 +549,12 @@ bool ELFAsmParser::ParseSectionArguments(bool IsPush, SMLoc loc) {
 
     if (extraFlags == -1U)
       return TokError("unknown flag");
+
+    // If we found additional section flags on a known section then give a
+    // warning.
+    if (Flags && Flags != extraFlags)
+      Warning(loc, "setting incorrect section attributes for " + SectionName);
+
     Flags |= extraFlags;
 
     bool Mergeable = Flags & ELF::SHF_MERGE;
diff --git a/test/MC/ELF/extra-section-flags.s b/test/MC/ELF/extra-section-flags.s
new file mode 100644
index 00000000000..c96516ee482
--- /dev/null
+++ b/test/MC/ELF/extra-section-flags.s
@@ -0,0 +1,10 @@
+# RUN: llvm-mc -triple x86_64-unknown-unknown -filetype=obj %s -o /dev/null 2>&1 | FileCheck %s
+	
+.section .rodata, "ax"
+# CHECK: warning: setting incorrect section attributes for .rodata
+nop
+
+.section .rodata, "a"
+# CHECK-NOT: warning:
+nop
+
-- 
2.11.0