C++: Letting compiler know asm block can call function that can throw?

[Stephan Bergmann]

On 03/29/2012 09:44 AM, Jakub Jelinek wrote:
> On Thu, Mar 29, 2012 at 09:05:29AM +0200, Stephan Bergmann wrote:
>> In LibreOffice's ever-beloved low-level code to synthesize calls to
>> C++ virtual functions, I'm having the following problem (on Linux
>> x86_64). The function callVirtualMethod at<http://cgit.freedesktop.org/libreoffice/core/tree/bridges/source/cpp_uno/gcc3_linux_x86-64/uno2cpp.cxx?id=571876c1234ae55aab0198c7e2caf9049fcd230e#n61>
>> effectively does the following:
>>
>> First, call dummy_can_throw_anything that can potentially throw (see
>> below for why that's there).  Second, in an asm block, call some
>> virtual function (that can potentially throw).  Third, call
>> x86_64::fill_struct that can potentially throw (it doesn't, but
>> nobody bothered to annotate it as "throw ()").
>
> If the asm isn't in headers, but just in a single short source file
> or two, you could try compiling that file with -fnon-call-exceptions.
> It is nothing I'd recommend for the whole codebase though.

Turns out I had to move the callVirtualMethod function containing the 
asm into a source file of its own, anyway.  (Otherwise, even if it no 
longer explicitly called functions that can throw, and thus no longer 
had corresponding .gcc_except_table entries, exception throwing still 
lead to std::terminate.  There are other functions in the same source 
file callVirtualMethod was originally in that do have .gcc_except_table 
entries.  Kind of invalidates my previous explanation of why exception 
handling bailed out to std::terminate.  Looks like I haven't groked it 
yet, anyway.)

So an explicit -fnon-call-exceptions on the command line seems to indeed 
help.  Unfortunately, moving that into a

   #pragma GCC optimize ("non-call-exceptions")

at the top of the source file that defines callVirtualMethod (and 
nothing more) does *not* work.  Is that a bug?

Anyway, would it be worthwhile filing an RFE for an asm annotation 
telling the compiler that it contains code that can throw?

Thanks,
Stephan