Fix BSS global handling in AsmPrinter

Change EmitGlobalVariable to check final assembler section is in BSS
before using .lcomm/.comm directive. This prevents globals from being
put into .bss erroneously when -data-sections is used.

This fixes PR26570.

Reviewers: echristo, rafael

Subscribers: llvm-commits, mehdi_amini

Differential Revision: http://reviews.llvm.org/D21146

llvm-svn: 272674

2 files changed, 51 insertions, 35 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 32f629eef74..d39881d9ce3 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -406,29 +406,42 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
     HI.Handler->setSymbolSize(GVSym, Size);
   }
 
-  // Handle common and BSS local symbols (.lcomm).
-  if (GVKind.isCommon() || GVKind.isBSSLocal()) {
+  // Handle common symbols
+  if (GVKind.isCommon()) {
     if (Size == 0) Size = 1;   // .comm Foo, 0 is undefined, avoid it.
     unsigned Align = 1 << AlignLog;
+    if (!getObjFileLowering().getCommDirectiveSupportsAlignment())
+      Align = 0;
 
-    // Handle common symbols.
-    if (GVKind.isCommon()) {
-      if (!getObjFileLowering().getCommDirectiveSupportsAlignment())
-        Align = 0;
+    // .comm _foo, 42, 4
+    OutStreamer->EmitCommonSymbol(GVSym, Size, Align);
+    return;
+  }
 
-      // .comm _foo, 42, 4
-      OutStreamer->EmitCommonSymbol(GVSym, Size, Align);
-      return;
-    }
+  // Determine to which section this global should be emitted.
+  MCSection *TheSection =
+      getObjFileLowering().SectionForGlobal(GV, GVKind, *Mang, TM);
 
-    // Handle local BSS symbols.
-    if (MAI->hasMachoZeroFillDirective()) {
-      MCSection *TheSection =
-          getObjFileLowering().SectionForGlobal(GV, GVKind, *Mang, TM);
-      // .zerofill __DATA, __bss, _foo, 400, 5
-      OutStreamer->EmitZerofill(TheSection, GVSym, Size, Align);
-      return;
-    }
+  // If we have a bss global going to a section that supports the
+  // zerofill directive, do so here.
+  if (GVKind.isBSS() && MAI->hasMachoZeroFillDirective() &&
+      TheSection->isVirtualSection()) {
+    if (Size == 0)
+      Size = 1; // zerofill of 0 bytes is undefined.
+    unsigned Align = 1 << AlignLog;
+    EmitLinkage(GV, GVSym);
+    // .zerofill __DATA, __bss, _foo, 400, 5
+    OutStreamer->EmitZerofill(TheSection, GVSym, Size, Align);
+    return;
+  }
+
+  // If this is a BSS local symbol and we are emitting in the BSS
+  // section use .lcomm/.comm directive.
+  if (GVKind.isBSSLocal() &&
+      getObjFileLowering().getBSSSection() == TheSection) {
+    if (Size == 0)
+      Size = 1; // .comm Foo, 0 is undefined, avoid it.
+    unsigned Align = 1 << AlignLog;
 
     // Use .lcomm only if it supports user-specified alignment.
     // Otherwise, while it would still be correct to use .lcomm in some
@@ -452,23 +465,6 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
     return;
   }
 
-  MCSymbol *EmittedInitSym = GVSym;
-
-  MCSection *TheSection =
-      getObjFileLowering().SectionForGlobal(GV, GVKind, *Mang, TM);
-
-  // Handle the zerofill directive on darwin, which is a special form of BSS
-  // emission.
-  if (GVKind.isBSSExtern() && MAI->hasMachoZeroFillDirective()) {
-    if (Size == 0) Size = 1;  // zerofill of 0 bytes is undefined.
-
-    // .globl _foo
-    OutStreamer->EmitSymbolAttribute(GVSym, MCSA_Global);
-    // .zerofill __DATA, __common, _foo, 400, 5
-    OutStreamer->EmitZerofill(TheSection, GVSym, Size, 1 << AlignLog);
-    return;
-  }
-
   // Handle thread local data for mach-o which requires us to output an
   // additional structure of data and mangle the original symbol so that we
   // can reference it later.
@@ -521,6 +517,8 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
     return;
   }
 
+  MCSymbol *EmittedInitSym = GVSym;
+
   OutStreamer->SwitchSection(TheSection);
 
   EmitLinkage(GV, EmittedInitSym);
diff --git a/llvm/test/CodeGen/X86/global-sections.ll b/llvm/test/CodeGen/X86/global-sections.ll
index ef1b1ac7524..ea6df468ceb 100644
--- a/llvm/test/CodeGen/X86/global-sections.ll
+++ b/llvm/test/CodeGen/X86/global-sections.ll
@@ -311,3 +311,21 @@ bb7:
 
 ; WIN32-SECTIONS: .section      .rdata,"dr",one_only,_G16
 ; WIN32-SECTIONS: _G16:
+
+; PR26570
+
+@G17 = internal global i8 0
+; LINUX: .type	G17,@object
+; LINUX: .local	G17
+; LINUX: .comm	G17,1,1
+
+; DARWIN: .zerofill __DATA,__bss,_G17,1,0
+
+; LINUX-SECTIONS: .type	G17,@object
+; LINUX-SECTIONS: .section	.bss.G17,"aw",@nobits
+; LINUX-SECTIONS: .byte	0
+; LINUX-SECTIONS: .size	G17, 1
+
+; WIN32-SECTIONS: .section	.bss,"bw",one_only,_G17
+; WIN32-SECTIONS: _G17:
+; WIN32-SECTIONS:.byte	0