On Fri, Nov 4, 2022 at 9:28 AM Sebastian Huber <sebastian.hu...@embedded-brains.de> wrote: > > Hello, > > even recent 32-bit architectures such as RISC-V do not support 64-bit > atomic operations. Using -fprofile-update=atomic for the 32-bit RISC-V > RV32GC ISA yields: > > warning: target does not support atomic profile update, single mode is > selected > > For multi-threaded applications it is quite important to use atomic > counter increments to get valid coverage data. I think this fall back is > not really good. Maybe we should consider using this approach from Jakub > Jelinek for 32-bit architectures lacking 64-bit atomic operations: > > if (__atomic_add_fetch_4 ((unsigned int *) &val, 1, __ATOMIC_RELAXED) > == 0) > __atomic_fetch_add_4 (((unsigned int *) &val) + 1, 1, > __ATOMIC_RELAXED); > > https://patchwork.ozlabs.org/project/gcc/patch/19c4a81d-6ecd-8c6e-b641-e257c1959...@suse.cz/#1447334 > > Last year I added the TARGET_GCOV_TYPE_SIZE target hook to optionally > reduce the gcov type size to 32 bits. I am not really sure if this was a > good idea. Longer running executables may observe counter overflows > leading to invalid coverage data. If someone wants atomic updates, then > the updates should be atomic even if this means to use a library > implementation (libatomic). > > What about the following approach if -fprofile-update=atomic is given: > > 1. Use 64-bit atomics if available. > > 2. Use > > if (__atomic_add_fetch_4 ((unsigned int *) &val, 1, __ATOMIC_RELAXED) > == 0) > __atomic_fetch_add_4 (((unsigned int *) &val) + 1, 1, > __ATOMIC_RELAXED); > > if 32-bit atomics are available. > > 3. Else use a library call (libatomic).
sounds good, though a library call would really be prohibitly expensive? > -- > embedded brains GmbH > Herr Sebastian HUBER > Dornierstr. 4 > 82178 Puchheim > Germany > email: sebastian.hu...@embedded-brains.de > phone: +49-89-18 94 741 - 16 > fax: +49-89-18 94 741 - 08 > > Registergericht: Amtsgericht München > Registernummer: HRB 157899 > Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler > Unsere Datenschutzerklärung finden Sie hier: > https://embedded-brains.de/datenschutzerklaerung/
