Prevent alias from pointing to weak aliases.

This adds back r204781.

Original message:

Aliases are just another name for a position in a file. As such, the
regular symbol resolutions are not applied. For example, given

define void @my_func() {
  ret void
}
@my_alias = alias weak void ()* @my_func
@my_alias2 = alias void ()* @my_alias

We produce without this patch:

        .weak   my_alias
my_alias = my_func
        .globl  my_alias2
my_alias2 = my_alias

That is, in the resulting ELF file my_alias, my_func and my_alias are
just 3 names pointing to offset 0 of .text. That is *not* the
semantics of IR linking. For example, linking in a

@my_alias = alias void ()* @other_func

would require the strong my_alias to override the weak one and
my_alias2 would end up pointing to other_func.

There is no way to represent that with aliases being just another
name, so the best solution seems to be to just disallow it, converting
a miscompile into an error.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204934 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola
2014-03-27 15:26:56 +00:00
parent 16dc6ed33f
commit f165cf7ce8
18 changed files with 58 additions and 61 deletions

View File

@@ -64,23 +64,15 @@ public:
Constant *getAliasee() {
return getOperand(0);
}
/// getAliasedGlobal() - Aliasee can be either global or bitcast of
/// global. This method retrives the global for both aliasee flavours.
/// This method tries to ultimately resolve the alias by going through the
/// aliasing chain and trying to find the very last global. Returns NULL if a
/// cycle was found.
GlobalValue *getAliasedGlobal();
const GlobalValue *getAliasedGlobal() const {
return const_cast<GlobalAlias *>(this)->getAliasedGlobal();
}
/// resolveAliasedGlobal() - This method tries to ultimately resolve the alias
/// by going through the aliasing chain and trying to find the very last
/// global. Returns NULL if a cycle was found. If stopOnWeak is false, then
/// the whole chain aliasing chain is traversed, otherwise - only strong
/// aliases.
GlobalValue *resolveAliasedGlobal(bool stopOnWeak = true);
const GlobalValue *resolveAliasedGlobal(bool stopOnWeak = true) const {
return const_cast<GlobalAlias *>(this)->resolveAliasedGlobal(stopOnWeak);
}
static bool isValidLinkage(LinkageTypes L) {
return isExternalLinkage(L) || isLocalLinkage(L) ||
isWeakLinkage(L) || isLinkOnceLinkage(L);