Commit Graph

11 Commits

Author SHA1 Message Date
Rafael Espindola 24a669d225 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.

llvm-svn: 204934
2014-03-27 15:26:56 +00:00
Rafael Espindola 65481d7b97 Revert "Prevent alias from pointing to weak aliases."
This reverts commit r204781.

I will follow up to with msan folks to see what is what they
were trying to do with aliases to weak aliases.

llvm-svn: 204784
2014-03-26 06:14:40 +00:00
Rafael Espindola 3b712a84a9 Prevent alias from pointing to weak aliases.
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.

llvm-svn: 204781
2014-03-26 04:48:47 +00:00
Rafael Espindola f3336bc1d5 Reject alias to undefined symbols in the verifier.
On ELF and COFF an alias is just another name for a position in the file.
There is no way to refer to a position in another file, so an alias to
undefined is meaningless.

MachO currently doesn't support aliases. The spec has a N_INDR, which when
implemented will have a different set of restrictions. Adding support for
it shouldn't be harder than any other IR extension.

For now, having the IR represent what is actually possible with current
tools makes it easier to fix the design of GlobalAlias.

llvm-svn: 203705
2014-03-12 20:15:49 +00:00
Reid Kleckner 22b19da9fc GlobalOpt: Aliases don't have sections, don't copy them when replacing
As defined in LangRef, aliases do not have sections.  However, LLVM's
GlobalAlias class inherits from GlobalValue, which means we can read and
set its section.  We should probably ban that as a separate change,
since it doesn't make much sense for an alias to have a section that
differs from its aliasee.

Fixes PR18757, where the section was being lost on the global in code
from Clang like:

extern "C" {
__attribute__((used, section("CUSTOM"))) static int in_custom_section;
}

Reviewers: rafael.espindola

Differential Revision: http://llvm-reviews.chandlerc.com/D2758

llvm-svn: 201286
2014-02-13 02:18:36 +00:00
Rafael Espindola 8d30480344 Always remove an alias when we rename the target.
Should fix the dragonegg build bots.

llvm-svn: 183845
2013-06-12 16:45:47 +00:00
Rafael Espindola fb3fc0bf34 Convert test to FileCheck.
llvm-svn: 183843
2013-06-12 16:35:53 +00:00
Dan Gohman 1880092722 Change tests from "opt %s" to "opt < %s" so that opt doesn't see the
input filename so that opt doesn't print the input filename in the
output so that grep lines in the tests don't unintentionally match
strings in the input filename.

llvm-svn: 81537
2009-09-11 18:01:28 +00:00
Dan Gohman 72a13d2476 Use opt -S instead of piping bitcode output through llvm-dis.
llvm-svn: 81257
2009-09-08 22:34:10 +00:00
Dan Gohman 9737a63ed8 Change these tests to feed the assembly files to opt directly, instead
of using llvm-as, now that opt supports this.

llvm-svn: 81226
2009-09-08 16:50:01 +00:00
Anton Korobeynikov a9b60ee0fc Resolve aliases, when possible
llvm-svn: 56001
2008-09-09 19:04:59 +00:00