On Sun, Jul 17, 2022 at 07:44:22AM -0700, Linus Torvalds wrote:
On Sun, Jul 17, 2022 at 2:13 AM Sudip Mukherjee
[off-list ref] wrote:
quoted
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