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[PowerPC] Revert r185476 and fix up TLS variant kinds

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In the commit message to r185476 I wrote:

>The PowerPC-specific modifiers VK_PPC_TLSGD and VK_PPC_TLSLD
>correspond exactly to the generic modifiers VK_TLSGD and VK_TLSLD.
>This causes some confusion with the asm parser, since VK_PPC_TLSGD
>is output as @tlsgd, which is then read back in as VK_TLSGD.
>
>To avoid this confusion, this patch removes the PowerPC-specific
>modifiers and uses the generic modifiers throughout.  (The only
>drawback is that the generic modifiers are printed in upper case
>while the usual convention on PowerPC is to use lower-case modifiers.
>But this is just a cosmetic issue.)

This was unfortunately incorrect, there is is fact another,
serious drawback to using the default VK_TLSLD/VK_TLSGD
variant kinds: using these causes ELFObjectWriter::RelocNeedsGOT
to return true, which in turn causes the ELFObjectWriter to emit
an undefined reference to _GLOBAL_OFFSET_TABLE_.

This is a problem on powerpc64, because it uses the TOC instead
of the GOT, and the linker does not provide _GLOBAL_OFFSET_TABLE_,
so the symbol remains undefined.  This means shared libraries
using TLS built with the integrated assembler are currently
broken.

While the whole RelocNeedsGOT / _GLOBAL_OFFSET_TABLE_ situation
probably ought to be properly fixed at some point, for now I'm
simply reverting the r185476 commit.  Now this in turn exposes
the breakage of handling @tlsgd/@tlsld in the asm parser that
this check-in was originally intended to fix.

To avoid this regression, I'm also adding a different fix for
this problem: while common code now parses @tlsgd as VK_TLSGD,
a special hack in the asm parser translates this code to the
platform-specific VK_PPC_TLSGD that the back-end now expects.
While this is not really pretty, it's self-contained and
shouldn't hurt anything else for now.  One the underlying
problem is fixed, this hack can be reverted again.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185945 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Ulrich Weigand
2013-07-09 16:41:09 +00:00
parent f2cfef8172
commit 7a34599db0
10 changed files with 73 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Target/PowerPC/PPCAsmPrinter.cpp
+4 -2
View File
@@ -573,7 +573,8 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
const GlobalValue *GValue = MO.getGlobal();
MCSymbol *MOSymbol = Mang->getSymbol(GValue);
const MCExpr *SymVar =
MCSymbolRefExpr::Create(MOSymbol, MCSymbolRefExpr::VK_TLSGD, OutContext);
MCSymbolRefExpr::Create(MOSymbol, MCSymbolRefExpr::VK_PPC_TLSGD,
OutContext);
OutStreamer.EmitInstruction(MCInstBuilder(PPC::BL8_NOP_TLS)
.addExpr(TlsRef)
.addExpr(SymVar));
@@ -624,7 +625,8 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
const GlobalValue *GValue = MO.getGlobal();
MCSymbol *MOSymbol = Mang->getSymbol(GValue);
const MCExpr *SymVar =
MCSymbolRefExpr::Create(MOSymbol, MCSymbolRefExpr::VK_TLSLD, OutContext);
MCSymbolRefExpr::Create(MOSymbol, MCSymbolRefExpr::VK_PPC_TLSLD,
OutContext);
OutStreamer.EmitInstruction(MCInstBuilder(PPC::BL8_NOP_TLS)
.addExpr(TlsRef)
.addExpr(SymVar));