Messages in this thread |  | | Date | Thu, 11 Jun 2020 18:52:56 -0500 | From | Segher Boessenkool <> | Subject | Re: [PATCH v4 1/2] powerpc/uaccess: Implement unsafe_put_user() using 'asm goto' |
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On Thu, Jun 11, 2020 at 03:43:55PM -0700, Nick Desaulniers wrote: > Segher, Cristophe, I suspect Clang is missing support for the %L and %U > output templates [1].
The arch/powerpc kernel first used the %U output modifier in 0c176fa80fdf (from 2016), and %L in b8b572e1015f (2008). include/asm-ppc (and ppc64) have had %U since 2005 (1da177e4c3f4), and %L as well (0c541b4406a6).
> I've implemented support for some of these before > in Clang via the documentation at [2], but these seem to be machine > specific?
Yes, almost all output modifiers are. Only %l, %a, %n, and part of %c are generic (and %% and %= and on some targets, %{, %|, %}).
> Can you please point me to documentation/unit tests/source for > these so that I can figure out what they should be doing, and look into > implementing them in Clang?
The PowerPC part of https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html#Machine-Constraints (sorry, no anchor) documents %U.
Traditionally the source code is the documentation for this. The code here starts with the comment /* Write second word of DImode or DFmode reference. Works on register or non-indexed memory only. */ (which is very out-of-date itself, it works fine for e.g. TImode as well, but alas).
Unit tests are completely unsuitable for most compiler things like this.
The source code is gcc/config/rs6000/rs6000.c, easiest is to search for 'L' (with those quotes). Function print_operand.
HtH,
Segher
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