Earlier today I wrote:
On 06/17/2013 08:41 AM, Joseph S. Myers wrote:
On Mon, 17 Jun 2013, Julian Brown wrote:
IIUC, the incompatibility between the specified
-fstrict-volatile-bitfields behaviour and the C++ memory model is a
recognised deficiency in the ARM EABI. It might be an unpopular
suggestion, but how about disabling the option by default for C++ on
ARM [*]? Maybe even with a "sorry" if the user tries to turn it on
manually?
The C11 and C++11 memory models are the same, this is nothing to do with
C++ as opposed to C.
The problem with always choosing C++ memory model compliance over ABI
compliance, no matter what the setting of -fstrict-volatile-bitfields,
is that some users may have legacy code out there where they really want
the ABI-compliant behavior. Perhaps we should not make
-fstrict-volatile-bitfields not be the default on any target any more,
but if you supply it explicitly it tells GCC that you really want the
ABI-compliant behavior to override the language-standard-compliant
behavior?
I had another thought: perhaps -fstrict-volatile-bitfields could remain
the default on targets where it currently is, but it can be overridden
by an appropriate -std= option. Perhaps also GCC could give an error if
-fstrict-volatile-bitfields is given explicitly with an incompatible
-std= option.
-Sandra
