PATCH: error on code that redeclares with an __asm__ label after the first ODR use

[Richard Smith via cfe-commits]

On Fri, Dec 11, 2015 at 12:43 PM, Gao, Yunzhong via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> gcc 4.8.2 accepts the following case silently without error or warning:
>
>   void f();
>
>   void g() __asm__(“real_g”);
>
>   void f() { g(); }  // gcc emits a call to real_g() here
>
>   void real_g() __asm__(“gold”);
>
> void real_g() { } // gcc generates a body for gold() here
>
>
>
> gcc 4.8.2 generates a warning for the following test case:
>
> void g() __asm__(“func1”);
>
> void g() __asm__(“func2”); // gcc generates a warning and ignores this asm
> label
>
> void g() { }
>
>
>
> Comparing to gcc behavior, I think it is better to emit error in both
> cases.
>

Why? I don't see anything wrong with the first example. We have a function
whose source-level name is "g()" and whose asm name is "real_g", and we
have a function whose source-level name is "real_g()" and whose asm name is
"gold". What's wrong with that?


> Looks good to me. Thanks!
>
> - Gao
>
>
>
>
>
> *From:* Nick Lewycky [mailto:nlewycky at google.com]
> *Sent:* Friday, December 11, 2015 12:44 AM
> *To:* Gao, Yunzhong
> *Cc:* Clang Commits
> *Subject:* Re: PATCH: error on code that redeclares with an __asm__ label
> after the first ODR use
>
>
>
> On 10 December 2015 at 17:42, Gao, Yunzhong <
> yunzhong_gao at playstation.sony.com> wrote:
>
> Out of curiosity, is the following test case possible too?
>
>
>
> void f();
>
> void g() __asm__(“real_g”); // rename g into real_g.
>
>
>
> void f() {
>
>   g(); // this would actually be calling real_g()
>
> }
>
> void real_g() __asm__("gold");  // re-declaring real_g() into gold <--
> should this be an error too?
>
>
>
> I can't see any reason why not. Both clang and gcc will emit "real_g" here
> instead of "gold", but changing the asm label in a program is highly
> dubious. I added an error for this too.
>
>
>
> Thanks!
>
>
>
> *From:* cfe-commits [mailto:cfe-commits-bounces at lists.llvm.org] *On
> Behalf Of *Nick Lewycky via cfe-commits
> *Sent:* Thursday, December 10, 2015 3:15 PM
> *To:* Clang Commits
> *Subject:* PATCH: error on code that redeclares with an __asm__ label
> after the first ODR use
>
>
>
> PR22830 shows a case where some code was adding an __asm__ label after the
> first use of a function. GCC and Clang diverged on this code, GCC emitting
> the name in the last __asm__ label for all uses while clang would switch in
> the middle of the TU as the redeclaration was parsed. The attached patch
> detects this case and issues an error on such a redeclaration. If this
> breaks real code, we can turn it down to a warning.
>
>
>
> Please review!
>
>
>
> Nick
>
>
>
>
>
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