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unix/README: Add some small documentation about sanitizers.

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Signed-off-by: Jeff Epler <jepler@gmail.com>
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Jeff Epler 2025-06-16 17:04:58 +02:00 committed by Damien George
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ports/unix/README.md
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@ -155,3 +155,21 @@ The default compiler optimisation level is -Os, or -Og if `DEBUG=1` is set.
Setting the variable `COPT` will explicitly set the optimisation level. For
example `make [other arguments] COPT=-O0 DEBUG=1` will build a binary with no
optimisations, assertions enabled, and debug symbols.
### Sanitizers
Sanitizers are extra runtime checks supported by gcc and clang. The CI process
supports building with the "undefined behavior" (UBSan) or "address" (ASan)
sanitizers. The script `tools/ci.sh` is the source of truth about how to build
and run in these modes.
Several classes of checks are disabled via compiler flags:
* In the undefined behavior sanitizer, checks based on the presence of the
`non_null` attribute are disabled because the code makes technically incorrect
calls like `memset(NULL, 0, 0)`. A future C standard is likely to permit such
calls.
* In the address sanitizer, `detect_stack_use_after_return` is disabled. This
check is intended to make sure locals in a "returned from" stack frame are not
used. However, this mode interferes with various assumptions that
MicroPython's stack checking, NLR, and GC rely on.