Messages in this thread |  | | Date | Sun, 17 Jul 2022 14:54:48 -0500 | From | Segher Boessenkool <> | Subject | Re: mainline build failure of powerpc allmodconfig for prom_init_check |
| |
On Sun, Jul 17, 2022 at 07:44:22AM -0700, Linus Torvalds wrote: > On Sun, Jul 17, 2022 at 2:13 AM Sudip Mukherjee > <sudipm.mukherjee@gmail.com> wrote: > > I was trying to check it. With gcc-11 the assembly code generated is > > not using memset, but using __memset. > > But with gcc-12, I can see the assembly code is using memset. One > > example from the assembly: > > You could try making the 'args' array in 'struct prom_args' be marked > 'volatile'. > > Ie something like this: > > --- a/arch/powerpc/kernel/prom_init.c > +++ b/arch/powerpc/kernel/prom_init.c > @@ -115,6 +115,6 @@ struct prom_args { > __be32 service; > __be32 nargs; > __be32 nret; > - __be32 args[10]; > + volatile __be32 args[10]; > }; > > because I think it's just the compilers turning the small loop over > those fields into a "memset()".
Yes. See <https://gcc.gnu.org/onlinedocs/gcc/Standards.html#C-Language> near the end: Most of the compiler support routines used by GCC are present in libgcc, but there are a few exceptions. GCC requires the freestanding environment provide memcpy, memmove, memset and memcmp. Finally, if __builtin_trap is used, and the target does not implement the trap pattern, then GCC emits a call to abort.
Can't we simply have a small simple implementation of these functions in arch/powerpc/boot/? This stuff is not performance-critical, and this is not the first time we hit these problems.
Segher
|  |