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Fix BSS global handling in AsmPrinter

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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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272674 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nirav Dave 2016-06-14 15:09:30 +00:00
parent da10a460d7
commit adf7e0e7c6
2 changed files with 51 additions and 35 deletions
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68
lib/CodeGen/AsmPrinter/AsmPrinter.cpp
View File

@ -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);

18
test/CodeGen/X86/global-sections.ll
View File

@ -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