Re: 64-bit int not being aligned in 32-bit ARM, causing crash
Re: 64-bit int not being aligned in 32-bit ARM, causing crash
- Subject: Re: 64-bit int not being aligned in 32-bit ARM, causing crash
- From: Jonas Maebe <email@hidden>
- Date: Wed, 11 Mar 2015 11:13:32 +0100
On 06 Mar 2015, at 02:50, Jens Alfke wrote:
Shouldn’t C alignment rules dictate that the ‘value’ union and the
surrounding ‘atomic_val_t’ type be 8-byte-aligned, since they
contain a 64-bit integer?
Alignment rules are not dictated by the programming language, but by
the ABI. The ARM ABI, and also Apple's variant, says that 64 bit
integers are only guaranteed 4 byte alignment: https://developer.apple.com/library/ios/documentation/Xcode/Conceptual/iPhoneOSABIReference/Articles/ARMv6FunctionCallingConventions.html
And if they don’t, what’s the workaround to ensure safe alignment?
Here's how to do it in gcc (aligned attribute), maybe it works the
same in clang: https://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html
Jonas
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