New submission from Oleksandr Pavlyk <oleksandr.pav...@intel.com>:
The following snippet illustrates request by an extension to use AMX registers:
```
// no increase sigaltstack size fix will not wark till we fix python
void enable_amx_no_fix()
{
unsigned long bitmask;
long rc;
rc = syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_PERM, XFEATURE_XTILEDATA);
if (rc) {
printf("The kernel rejects the AMX use.\n");
printf("errno %d\n",errno);
} else {
printf("The kernel allows to use AMX.\n");
}
rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_PERM, &bitmask);
if (rc) {
printf("rc error\n");
} else {
if (( bitmask & XFEATURE_MASK_XTILEDATA) == 0){
printf("verify AMX permission faild bitmask %ld\n",bitmask);
}
}
}
```
This request fails on the account of too small a size for sigaltstack used by
CPython allocated in Modules/faulthandler.c
The stack size used is 2*SIGSTKSZ, and does not take hardware capabilities into
account.
Linux kernel 5.14 adds support to query minimum size of sigaltstack dynamically
via getauxval(AT_MINSIGSTKSZ).
AMX support is added in Linux kernel 5.16
CPython should make use of this when built against more recent Linux kernels.
----------
components: Extension Modules
messages: 414809
nosy: oleksandr-pavlyk
priority: normal
severity: normal
status: open
title: Insufficient sigaltstack size used by CPython prevents extensions from
using new ISA
type: behavior
versions: Python 3.10, Python 3.11, Python 3.7, Python 3.8, Python 3.9
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue46968>
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