Array indexing/offset inline asm ambiguity

John Colvin john.loughran.colvin at gmail.com
Sat Mar 16 18:46:49 PDT 2013


On Sunday, 17 March 2013 at 00:24:16 UTC, David Nadlinger wrote:
> Hi all,
>
> Another installment in the »What does the following function 
> return« series:
>
> ---
> int[2] foo() {
>   int[2] regs;
>   asm {
>     mov regs[1], 0xdeadbeef;
>   }
>   return regs;
> }
> ---
>
> If you answered [0, 0xdeadbeef], then congratulations: You fell 
> into exactly the same trap as Martin Nowak and I did in 
> https://github.com/D-Programming-Language/druntime/pull/426, 
> without any of the other reviewers noticing either.
>
> The issue is that in an inline asm block, regs[1] is actually 
> equivalent to 1[regs] or [regs + 1] and evaluates to an address 
> one *byte* after the start of regs, not one element as it does 
> everywhere else.
>
> In my opinion, this is completely counterintuitive and a source 
> of bugs that could easily be prevented by the language. But 
> Walter seems to think this issue not worth addressing: 
> http://d.puremagic.com/issues/show_bug.cgi?id=9738
>
> What do you think?
>
> Thanks,
> David

D syntax should have D semantics, even in inline asm. (where that 
syntax does not conflict with the asm syntax of course)


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