AArch64: fix cpuinfo issues

[pawosm01]

Summary

AArch64: fix an issue with older /proc/cpuinfo layout

There are two /proc/cpuinfo layots in use for AArch64: old and new.
The old one has all 'processor : n' lines in one section, hence
checking for duplications does not make sense.

[Hahnfeld]

I already have https://reviews.llvm.org/D40357 for review which does the same (except skipping the duplicate cpuinfo). It is currently blocked by https://reviews.llvm.org/D40722, maybe you could take a look there, ARM should suffer from the same problem.

[Hahnfeld]

runtime/src/kmp_affinity.cpp

2032 ↗

(On Diff #126279)

Multiple questions here, could you maybe add some comments with the answers?

1. This can only happen for the "old" format? And we can't diagnose duplicate field errors in the new format because we just assume that we are seeing the old format, right?
2. The "old" format doesn't have other information than the "processor <id>" specified? Because the code further down relies on num_avail pointing to the current entry.

[pawosm01]

Example of old format layout (note that 'Processor :' and 'processor :' won't collide as we don't call strncasecmp()):

$ cat /proc/cpuinfo
Processor : Cortex A57 Processor rev 1 (aarch64)
processor : 0
processor : 1
processor : 2
processor : 3
Features : fp asimd aes pmull sha1 sha2 crc32
CPU implementer : 0x41
CPU architecture: AArch64
CPU variant : 0x1
CPU part : 0xd07
CPU revision : 1

Hardware : jetson_tx1
Revision : 0000
Serial : xxxxxxx
$

Brief analysis of the code (after my changes) showed it does the right thing for the example above. This pattern (two sections, "Processor" and "Hardware" with all the "processor" entries listed only in the first one) is consistent across different machines with old /proc/cpuinfo layout.

[Hahnfeld]

LGTM if you add a comment in the code explaining why we need this (old format) and that this effectively disables error detection in the new format on AArch64

openmp/trunk/runtime/src/kmp_affinity.cpp

return -1;                                                                 \
       char s1[] = "processor";
       if (strncmp(buf, s1, sizeof(s1) - 1) == 0) {
         CHECK_LINE;
         char *p = strchr(buf + sizeof(s1) - 1, ':');
         unsigned val;
         if ((p == NULL) || (KMP_SSCANF(p + 1, "%u\n", &val) != 1))
           goto no_val;
         if (threadInfo[num_avail][osIdIndex] != UINT_MAX)
+#if KMP_ARCH_AARCH64
+          // Handle the old AArch64 /proc/cpuinfo layout differently,
+          // it contains all of the 'processor' entries listed in a
+          // single 'Processor' section, therefore the normal looking
+          // for duplicates in that section will always fail.
+          num_avail++;
+#else
           goto dup_field;
+#endif
         threadInfo[num_avail][osIdIndex] = val;
 #if KMP_OS_LINUX && !(KMP_ARCH_X86 || KMP_ARCH_X86_64)
         char path[256];
         KMP_SNPRINTF(
             path, sizeof(path),
             "/sys/devices/system/cpu/cpu%u/topology/physical_package_id",
             threadInfo[num_avail][osIdIndex]);
         __kmp_read_from_file(path, "%u", &threadInfo[num_avail][pkgIdIndex]);