On Fri, 14 Oct 2022 12:56:48 PDT (-0700), Palmer Dabbelt wrote:
We have had an implementation of __builtin___clear_cache since the beginning, but didn't have the cooresponding __clear_cache library routine implemented. This directly conflicts the GCC manual in a handful of places, which indicates that __clear_cache should work and that __builtin_clear_cache should function the same way as __clear_cache by ethier calling it or inlining the functionality.This patch simply implements __clear_cache via __builtin___clear_cache. This should be safe as we always have clear_cache insn so therefor __builtin___clear_cache will never fall back to calling __clear_cache. I'm not actually sure that silently implementing clear_cache as a NOP when there is no ISA defined mechanism for icache synchronization is the right way to go, but that's really a different discussion. This was reported as Bug 94136, which is a year old but was categorized as a documentation bug. I believe that categorization was incorrect: having an empty __clear_cache library routine is simply incorrect behavior, the fact that __builtin___clear_cache happens to be implemented as a libc call on Linux is just a red herring suggesting the documentation fix to point out the name difference. I view this new behavior as conforming to the existing documentation: we're just inlining the __clear_cache implementation, even if that implementation happens to be a call to a very similar looking libc routine. gcc/ChangeLog PR target/94136 * config/riscv/riscv.h (CLEAR_INSN_CACHE): New macro. --- Passes riscv-linux mulilib with no new failures. OK for trunk and
Oops, accidentally hit send before checking the test results. There's a bunch of failures, not sure if they're new though as I was trying to bisect them down and have a dirty tree. This might take a few minutes...
backports to gcc-11, gcc-12? Changes since v1 <20210430045646.1508805-1-palmerdabb...@google.com>: * Extra "_" as per Jim's comment. --- gcc/config/riscv/riscv.h | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/gcc/config/riscv/riscv.h b/gcc/config/riscv/riscv.h index acae68ebb2d..bb0dcb651d5 100644 --- a/gcc/config/riscv/riscv.h +++ b/gcc/config/riscv/riscv.h @@ -1080,4 +1080,9 @@ extern void riscv_remove_unneeded_save_restore_calls (void); #define REGISTER_TARGET_PRAGMAS() riscv_register_pragmas () +/* We always have a "clear_cache" insn, which means __builtin__clear_cache will + never emit a call to __clear_cache. */ +#undef CLEAR_INSN_CACHE +#define CLEAR_INSN_CACHE(BEG, END) __builtin___clear_cache((BEG), (END)); + #endif /* ! GCC_RISCV_H */
