[cxx-abi-dev] Mangling of string literals versus variadic templates

[John McCall]

On Dec 17, 2013, at 6:34 PM, Richard Smith <richardsmith at google.com> wrote:
> On Tue, Dec 17, 2013 at 5:47 PM, David Vandevoorde <daveed at edg.com> wrote:
> 
> On Dec 17, 2013, at 5:22 PM, John McCall <rjmccall at apple.com> wrote:
> 
>> On Dec 17, 2013, at 12:01 PM, Sean Hunt <scshunt at csclub.uwaterloo.ca> wrote:
>>> On Tue, Dec 17, 2013 at 2:57 PM, John McCall <rjmccall at apple.com> wrote:
>>> On Dec 17, 2013, at 11:12 AM, David Vandevoorde <daveed at edg.com> wrote:
>>> > On Dec 16, 2013, at 8:33 PM, John McCall <rjmccall at apple.com> wrote:
>>> >> On Dec 16, 2013, at 5:10 PM, Richard Smith <richardsmith at google.com> wrote:
>>> >>> Consider:
>>> >>
>>> >> Remind me why it’s impossible to go back to the committee and repeatedly weaken any remaining guarantees about string literal addresses until none of this is important?
>>> >
>>> > I don't know if it's impossible or not, but I suspect it would be controversial.  (I, at least, would be opposed.)
>>> 
>>> Really?  You feel that having really strong guarantees about the address of a string literal is the right thing to do?  Like, it’s worth significantly increasing build times, code size, and launch times over?
>>> 
>>> John.
>>> 
>>> I don't see a situation where baz() below returns false really being defensible:
>> 
>> Why?  Who cares?  Why is “don’t rely on string literal addresses being consistent” actually an unreasonable piece of advice?  Because I’m pretty sure that’s the advice that everybody’s been rolling with for over thirty years now.
> 
> 
> We put in the C++ rules about 20 years ago because people wanted to have
> 
> 	inline char const* name() { return "SomeName"; }
> 
> return the name pointer value in every TU (I think that's reasonable). There is certainly still plenty of code relying on that.
> 
> I find that a little surprising, since GCC does not guarantee this, and it is the system compiler on a lot of platforms. (Likewise, Clang does not, and is the system compiler on some platforms). There's a GCC bug on this with only two duplicates, and no Clang bug has been filed, so I don't get the impression that this is a big deal for a lot of people on Linux or Mac.
> 
> On the other hand, MSVC guarantees something much stronger: it appears to give *all* string literals a mangled name comprising their type, the first few (32?) characters of the string, and a checksum of the rest.

Hmm, that’s interesting.  I wonder how that interacts with their string-pooling option (/GF), which is what I was looking at before.

I assume that the mangled name isn’t exported from the DLL, though.

John.
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