On Wed, 20 Nov 2024 16:20:59 GMT, Magnus Ihse Bursie <i...@openjdk.org> wrote:
> First of all, building stuff with `--with-extra-cflags` is always at your own > peril. It might, or might not, work, partially due to problems such as the > one you describe, where the user-added flag somehow conflicts with the > existing flag. If you wish to modify the build in ways that is not compatible > with the existing build logic, you might end up needed a local patch to be > applied, and not just adding the `--with-extra-cflags` command line. > > With that said, we will try to make it as possible as reasonable to write the > build system for flexibility. > > In this case: what do you propose we would have done instead? My > understanding is that the compiler needs to be told about SVE in order to > compile libsleef properly. It is right to tell the compiler about `+sve` for libsleef compilation, while the concerning point is `-march=armv8-a`. I agreed that using `armv8-a` could be a safer way to a build-system. However it invalidates the ability of `--with-extra-cflags` of specifying any proper `-march=` or `-mcpu=`. Note that the user knows very well about what to build and where to run, but has no way to change things without modifying sources. For example, if one sets `--with-extra-cflags=-march=armv9.1-a` for any equivalent `-mcpu=`, why libsleef still wants to use `armv8-a` with downgraded version of ISA? I don't think one should use "a local path" here as it would be contrary to the intent of having autoconf and the design of `--with-extra-cflags`. Frankly speaking, no better idea from me either. Trying to update user specified `-march=` might be a way, such as `-march=armv9.1-a+sve` in above example, but perhaps it generates a new violation of the rules - `not to modify user inputs`. Leaving the "cc1: warning" message there for the time being could be also fine as it only impacts libsleef, while it warns the potential issue, for any future resolving. FYI, aarch64 modifiers https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html#g_t-march-and--mcpu-Feature-Modifiers arch value | Architecture | Includes by default -- | -- | -- ‘**armv8-a**’ | Armv8-A | ‘+fp’, ‘+simd’ ‘armv8.1-a’ | Armv8.1-A | ‘armv8-a’, ‘+crc’, ‘+lse’, ‘+rdma’ ‘armv8.2-a’ | Armv8.2-A | ‘armv8.1-a’ ‘armv8.3-a’ | Armv8.3-A | ‘armv8.2-a’, ‘+pauth’ ‘armv8.4-a’ | Armv8.4-A | ‘armv8.3-a’, ‘+flagm’, ‘+fp16fml’, ‘+dotprod’ ‘armv8.5-a’ | Armv8.5-A | ‘armv8.4-a’, ‘+sb’, ‘+ssbs’, ‘+predres’ ‘armv8.6-a’ | Armv8.6-A | ‘armv8.5-a’, ‘+bf16’, ‘+i8mm’ ‘armv8.7-a’ | Armv8.7-A | ‘armv8.6-a’ ‘armv8.8-a’ | Armv8.8-a | ‘armv8.7-a’, ‘+mops’ ‘armv8.9-a’ | Armv8.9-a | ‘armv8.8-a’ ‘armv9-a’ | Armv9-A | ‘armv8.5-a’, ‘**+sve**’, ‘+sve2’ ‘armv9.1-a’ | Armv9.1-A | ‘armv9-a’, ‘+bf16’, ‘+i8mm’ ‘armv9.2-a’ | Armv9.2-A | ‘armv9.1-a’ ‘armv9.3-a’ | Armv9.3-A | ‘armv9.2-a’, ‘+mops’ ‘armv9.4-a’ | Armv9.4-A | ‘armv9.3-a’ ‘armv8-r’ | Armv8-R | ‘armv8-r’ ------------- PR Comment: https://git.openjdk.org/jdk/pull/18294#issuecomment-2490088547
