On 07/16/2014 11:00 AM, Jakub Jelinek wrote:
On Wed, Jul 16, 2014 at 10:55:57AM +0200, Florian Weimer wrote:
On 07/15/2014 07:22 PM, Adam Jackson wrote:
On Tue, 2014-07-15 at 10:40 -0600, Orion Poplawski wrote:
Did you know that "char" defaults to "signed char" on x86 but "unsigned char"
on ppc and arm? I didn't.
Yep, found that out the hard way. It annoyed me enough that I went
digging in the gcc source to find the answer for all platforms:
http://ajax.fedorapeople.org/is-char-signed-or-not.txt
Any idea why aarch64 and ppc64le got this wrong?
Why is char == unsigned char wrong? Because i?86/x86_64 do it differently?
Yes, it looks like a totally avoidable portability hazard. iOS has
signed chars as well, so even when considering current ARM, the natural
choice is unclear. Older ARMs couldn't perform sign-extending 8-bit
loads in a single instruction, but that's true for historic x86, too,
and yet even the old 16-bit compilers used signed chars.
History aside, I assumed that the idea behind both architectures
(aarch64 and ppc64le) is to use it to run current general-purpose server
loads, and those are predominantly x86 right now. That's why picking
unsigned chars puzzles me.
--
Florian Weimer / Red Hat Product Security
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