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Re: [RFC] Fix for PR driver/47785


On 01/23/13 15:36, Richard Biener wrote:
On Tue, Jan 22, 2013 at 5:00 PM, Ramana Radhakrishnan <ramrad01@arm.com> wrote:
Hi,

I ran into PR driver/47785 when doing some testing with an option passed to
the testsuite and I chose to fix this by putting out COLLECT_AS_OPTIONS as
though these are options for the driver by prepending them with a "'-Wa",
and suffixing them with a "'" character and additionally providing spaces as
duly required. I've chosen a simple implementation.

Tested in the past with x86_64-linux-gnu and arm-none-eabi cross tests (with
an additional -Wa option passed to the default flags in a site.exp)

Thoughts ?

Ok for trunk now or should I stage this for 4.9 ?

I don't think this fix will work reliably - it's probably desirable anyway for other uses of -Wa,... but providing a symbol definition is something that needs to be understood by LTO at WPA time, otherwise we will get confusing / wrong symbol resolutions and eventually wrong code generated in the end. Thus with the patch you get some false sense of security I think (consider -fno-fat-lto-objects, you'd get x UNDEFed, and with -ffat-lto-objects you'd get a prevailing IRONLY def but the symbol wasn't in the LTO symbol table and we don't find a prevailing definition at WPA time ...)

Can you define a symbol on the command line for the assembler ? I didn't know GAS or assemblers could do that and even if it did, I don't understand why ...


The linker allows you a -Wl,--defsym=foo=<val> or whatever you want to do there, so even if the assembler were to have an undef reference to a symbol in an object file, it would get fixed up at link time by the linker.

So if you are saying that we need to make LTO handle -Wl, --defsym=sym=<value> I'd envisage the need to handle potential confusion but even that's a separate patch and unrelated to this one ...... :)

Intrigued :)

cheers,
Ramana



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