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Re: GCC turns &~ into | due to undefined bit-shift without warning
On 20/03/2019 15:08, Moritz Strübe wrote:
Hey.
Am 11.03.2019 um 12:17 schrieb Jakub Jelinek:
On Mon, Mar 11, 2019 at 11:06:37AM +0000, Moritz Strübe wrote:
On 11.03.2019 at 10:14 Jakub Jelinek wrote:
You could build with -fsanitize=undefined, that would tell you at runtime you
have undefined behavior in your code (if the SingleDiff has bit ever 0x20
set).
Yes, that helps. Unfortunately I'm on an embedded system, thus the code
size increase is just too big.
You can -fsanitize-undefined-trap-on-error, which doesn't increase size too
much, it is less user-friendly, but still should catch the UB.
Wouldn't this fail to link? I thought the sanitizers need some runtime libraries which are only available under linux/macos/android. What do you mean by embedded? Isn't it arm-eabi?
Ok, I played around a bit. Interestingly, if I set -fsanitize=udefined and -fsanitize-undefined-trap-on-error the compiler detects that it will always trap, and optimizes the code accordingly (the code after the trap is removed).* Which kind of brings me to David's argument: Shouldn't the compiler warn if there is undefined behavior it certainly knows of?
I do assume though that fsanitize just injects the test-code everywhere and relies on the compiler to remove it at unnecessary places. Would be nice, though. :)
Could you confirm in which version of the ST libraries you noticed this bug?
I'm told it was fixed on 23-march-2018.
Thanks,
Christophe
Cheers
Morty
*After fixing the code, it got too big to fit.
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