PNaCl ABI: Disallow the "available_externally" linkage type

"define available_externally void @foo()" would mean that the
definition of foo() can be dropped from the pexe, because a definition
of foo() can be found in an external native library.  This is not
something we support for a PNaCl pexe.

Clang generates "available_externally" for non-static inline function
definitions at -O1, but not at -O0, and generally not at -O2 either
because inlining removes the "available_externally" definition.

"available_externally" gets removed at bitcode link time, so we can
disallow it in the ABI checker without any further work required.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3495
TEST=*.ll tests + PNaCl toolchain trybots

Review URL: https://codereview.chromium.org/17035015

2 files changed, 7 insertions, 2 deletions

diff --git a/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp b/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp
index c0a5e4bcc2..2cc6572606 100644
--- a/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp
+++ b/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp
@@ -108,7 +108,6 @@ void PNaClABIVerifyModule::checkGlobalValueCommon(const GlobalValue *GV) {
   switch (GV->getLinkage()) {
     // TODO(dschuff): Disallow external linkage
     case GlobalValue::ExternalLinkage:
-    case GlobalValue::AvailableExternallyLinkage:
     case GlobalValue::InternalLinkage:
       break;
     default:
diff --git a/test/NaCl/PNaClABI/linkagetypes.ll b/test/NaCl/PNaClABI/linkagetypes.ll
index 61a5286838..fffaadc2ee 100644
--- a/test/NaCl/PNaClABI/linkagetypes.ll
+++ b/test/NaCl/PNaClABI/linkagetypes.ll
@@ -35,6 +35,7 @@ target triple = "le32-unknown-nacl"
 @gv_extern_weak = extern_weak global [1 x i8]
 ; CHECK: gv_extern_weak has disallowed linkage type: extern_weak
 @gv_avilable_externally = available_externally global [1 x i8] c"x"
+; CHECK: gv_avilable_externally has disallowed linkage type: available_externally
 
 
 ; CHECK-NOT: disallowed
@@ -75,4 +76,9 @@ define dllexport void @dllexport_func() {
 }
 ; CHECK-NEXT: Function extern_weak_func is declared but not defined (disallowed)
 ; CHECK-NEXT: Function extern_weak_func has disallowed linkage type: extern_weak
-declare extern_weak void @extern_weak_func()
\ No newline at end of file
+declare extern_weak void @extern_weak_func()
+
+; CHECK-NEXT: Function avail_ext_func has disallowed linkage type: available_externally
+define available_externally void @avail_ext_func() {
+  ret void
+}