Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC

Commits:

• 86406f48
  by Cheng Shao at 2025-05-20T09:19:47-04:00

  rts: fix rts_clearMemory logic when sanity checks are enabled
  
  This commit fixes an RTS assertion failure when invoking
  rts_clearMemory with +RTS -DS. -DS implies -DZ which asserts that free
  blocks contain 0xaa as the designated garbage value. Also adds the
  sanity way to rts_clearMemory test to prevent future regression.
  Closes #26011.
  
  ChatGPT Codex automatically diagnosed the issue and proposed the
  initial patch in a single shot, given a GHC checkout and the following
  prompt:
  
  ---
  
  Someone is reporting the following error when attempting to use `rts_clearMemory` with the RTS option `-DS`:
  
  ```
  test.wasm: internal error: ASSERTION FAILED: file rts/sm/Storage.c, line 1216
  
      (GHC version 9.12.2.20250327 for wasm32_unknown_wasi)
      Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug
  ```
  
  What's the culprit? How do I look into this issue?
  
  ---
  
  I manually reviewed & revised the patch, tested and submitted it.
  

2 changed files:

• rts/sm/Storage.h
• testsuite/tests/ffi/should_run/all.T

Changes:

 extern StgIndStatic * revertible_caf_list;

 INLINE_HEADER void clear_blocks(bdescr *bd) {

-   memset(bd->start, 0, BLOCK_SIZE * bd->blocks);

+  memset(bd->start, RtsFlags.DebugFlags.zero_on_gc ? 0xaa : 0,

+         BLOCK_SIZE * bd->blocks);

 }

 #include "EndPrivate.h"

 test('rts_clearMemory', [

      # We only care about different GC configurations under the

      # single-threaded RTS for the time being.

-     only_ways(['normal', 'optasm' ,'g1', 'nursery_chunks', 'nonmoving', 'compacting_gc']),

-     extra_ways(['g1', 'nursery_chunks', 'nonmoving', 'compacting_gc']),

+     only_ways(['normal', 'optasm' ,'g1', 'nursery_chunks', 'nonmoving', 'compacting_gc', 'sanity']),

+     extra_ways(['g1', 'nursery_chunks', 'nonmoving', 'compacting_gc', 'sanity']),

      # On windows, nonmoving way fails with bad exit code (2816)

      when(opsys('mingw32'), fragile(23091)),

      req_c,