On 16.07.2018 00:00, Kamil Rytarowski wrote: > On 15.07.2018 20:08, Christos Zoulas wrote: >> Hi, >> >> Gcc is now working on aarch64 but the kernel does not compile because of >> some idiomatic clang code that is not supported by gcc (at least gcc-6) >> >> To define constants, it uses: >> >> static const uintmax_t >> FOO = __BIT(9), >> BAR = FOO; >> >> While this is nice, specially for the debugger, it produces an error >> in gcc. While fixing these is easy, gcc also complains about using the >> constants as switch labels. Thus it is better to just nukem all and >> rewrite them as: >> >> #define FOO __BIT(9) >> #define BAR FOO >> >> Should I go ahead and do it, or there is a smarter solution? >> >> christos >> > > I used to have problems to build rumpkernel aarch64 on Linux with GCC > (some years ago) due to usage __uint128_t in reg.h. > > Can we drop it? The __uint128_t type is not used anywhere else in > aarch64 subdirs. > > It's used in assembly in FPREG_Q0-FPREQ_Q31 in cpuswitch.S. The same > optimization can be done without the usage of __uint128_t, probably just > need for proper alignment of fp_reg (15).
16* > > There is also some mysterious fallout that General Purpose Registers in > core files are shipped with 128bit containers. It's not compatible with > LLDB and requires needless generic work for no purpose. > > I can try to prepare a patch blindly and share with aarch64 owners. > Looking deeper, there are various reports regarding aarch64 128-bit broken support. "Be careful of GCC's __uint128_t. It caused us problems on a number of platforms, like ARM64, ARMEL and S/390. We had to give up using it because it was so buggy. For example, GCC calculated the result of u = 93 - 0 - 0 - 0 (using the 128-bit types) as 18446744073709551615 on ARM64" https://stackoverflow.com/questions/11656241/how-to-print-uint128-t-number-using-gcc There are no utility features for such numbers such as PRIu128, no support in printf(3), snprintf(3) etc. I will prepare a patch for removal of this from public machine headers.
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