[all-commits] [llvm/llvm-project] 3b8ac7: [OpenMP] Fix various alignment issues (#142376)

[Rainer Orth via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 3b8ac7a22c649d42e748b93d67ac237a85524328
      https://github.com/llvm/llvm-project/commit/3b8ac7a22c649d42e748b93d67ac237a85524328
  Author: Rainer Orth <ro at gcc.gnu.org>
  Date:   2025-06-25 (Wed, 25 Jun 2025)

  Changed paths:
    M openmp/runtime/src/kmp_alloc.cpp
    M openmp/runtime/src/kmp_csupport.cpp
    M openmp/runtime/src/kmp_tasking.cpp

  Log Message:
  -----------
  [OpenMP] Fix various alignment issues (#142376)

When running the `openmp` testsuite on 32-bit SPARC, several tests
`FAIL` apparently randomly, but always with the same kind of error:
```
# error: command failed with exit status: -11
```
The tests die with `SIGBUS`, as can be seen in `truss` output:
```
26461/1:            Incurred fault #5, FLTACCESS  %pc = 0x00010EAC
26461/1:              siginfo: SIGBUS BUS_ADRALN addr=0x0013D12C
26461/1:            Received signal #10, SIGBUS [default]
26461/1:              siginfo: SIGBUS BUS_ADRALN addr=0x0013D12C
```
i.e. the code is trying an unaligned access which cannot work on SPARC,
a strict-alignment target which enforces natural alignment on access.
This explains the apparent randomness of the failures: if the memory
happens to be aligned appropriately, the tests work, but fail if not.

A `Debug` build reveals much more:

- `__kmp_alloc` currently aligns to `sizeof(void *)`, which isn't enough
on strict-alignment targets when the data are accessed as types
requiring larger alignment. Therefore, this patch increases `alignment`
to `SizeQuant`.

- 32-bit Solaris/sparc `libc` guarantees 8-byte alignment from `malloc`,
so this patch adjusts `SizeQuant` to match.

- There's a `SIGBUS` in
  ```
  __kmpc_fork_teams (loc=0x112f8, argc=0, 
microtask=0x16cc8
<__omp_offloading_ffbc020a_4b1abe_main_l9_debug__.omp_outlined>)
      at openmp/runtime/src/kmp_csupport.cpp:573
  573	  *(kmp_int64 *)(&this_thr->th.th_teams_size) = 0L;
  ```
Casting to a pointer to a type requiring 64-bit alignment when that
isn't guaranteed is wrong. Instead, this patch uses `memset` instead.

- There's another `SIGBUS` in
  ```
0xfef8cb9c in __kmp_taskloop_recur (loc=0x10cb8, gtid=0, task=0x23cd00,
lb=0x23cd18, ub=0x23cd20, st=1, ub_glob=499, num_tasks=100, grainsize=5,
      extras=0, last_chunk=0, tc=500, num_t_min=20, 
codeptr_ra=0xfef8dbc8 <__kmpc_taskloop(ident_t*, int, kmp_task_t*, int,
kmp_uint64*, kmp_uint64*, kmp_int64, int, int, kmp_uint64, void*)+240>,
      task_dup=0x0)
      at openmp/runtime/src/kmp_tasking.cpp:5147
  5147	  p->st = st;
  ```
`p->st` doesn't currently guarantee the 8-byte alignment required by
`kmp_int64 st`. `p` is set in
  ```
   __taskloop_params_t *p = (__taskloop_params_t *)new_task->shareds;
  ```
but `shareds_offset` is currently aligned to `sizeof(void *)` only.
Increasing it to `sizeof(kmp_uint64)` to match its use fixes the
`SIGBUS`.

With these fixes I get clean `openmp` test results on 32-bit SPARC (both
Solaris and Linux), with one unrelated exception.

Tested on `sparc-sun-solaris2.11`, `sparcv9-sun-solaris2.11`,
`sparc-unknown-linux-gnu`, `sparc64-unknown-linux-gnu`,
`i386-pc-solaris2.11`, `amd64-pc-solaris2.11`, `i686-pc-linux-gnu`, and
`x86_64-pc-linux-gnu`.



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