emitbc: Avoid undefined behavior calling memset() #3799
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When micropython is built with 'clang -fsanitize=undefined', a diagnostic
like the following will occur:
$ UBSAN_OPTIONS=abort_on_error=1 ./micropython_fuzzing -c 'print(1)'
../../py/emitbc.c:319:16: runtime error: null pointer passed as argument 1, which is declared to never be null
/usr/include/string.h:62:62: note: nonnull attribute specified here
Aborted
Traditionally, memset(NULL, value, 0) has been accepted without causing
problems. However, it is not standards-compliant behavior; and for
instance Ted Unangst of the OpenBSD project notes that "A smart C compiler
may observe a call to memcpy, flag both pointers as valid, and then
delete any null checks. Forwards and backwards."
https://www.tedunangst.com/flak/post/zero-size-objects
Since micropython is using -fdelete-null-pointer-checks ("enabled by
default on most targets") and it is probably giving good code size
improvements, we have to pay a modest price and add a few checks.
|
Thanks! I agree with the analysis here, than memset should not be passed NULL and so the right thing to do is check the pointer first (because it is NULL on the first pass of the compiler). Merged in bc6c0b2 |
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Dec 8, 2020
Include wifi.radio singleton in gc
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When micropython is built with 'clang -fsanitize=undefined', a diagnostic like the following will occur:
Traditionally, memset(NULL, value, 0) has been accepted without causing problems. However, it is not standards-compliant behavior; and for instance Ted Unangst of the OpenBSD project notes that "A smart C compiler may observe a call to memcpy, flag both pointers as valid, and then delete any null checks. Forwards and backwards."
https://www.tedunangst.com/flak/post/zero-size-objects
Since micropython is using -fdelete-null-pointer-checks ("enabled by default on most targets") and it is probably giving good code size improvements, we have to pay a modest price and add a few checks.