Re:Pointers Are Complicated, or What’s in a Byte?
by vardump on Wednesday July 25, 2018 @05:20AM
(#17607924)
I read "memory is untouched" as no read/write accesses.
Because it'd be pretty odd for the page to change after first read from operating system implementation point of view. Generally I'd expect the default mapping to be to an all-zero physical memory page. (Unless there's a rowhammer attack (or similar) that successfully modifies said all-zero page...)
From C/C++ point of view, it's legal for uninitialized memory to arbitrarily change between (undefined behavior) reads until it is written to.
While I doubt any actual OS would modify the page in this manner after first read access, a C/C++ compiler can still return arbitrary (even random) values when reading from uninitialized memory. It doesn't even need to actually read from the memory proven to be uninitialized.
Because it'd be pretty odd for the page to change after first read from operating system implementation point of view. Generally I'd expect the default mapping to be to an all-zero physical memory page. (Unless there's a rowhammer attack (or similar) that successfully modifies said all-zero page...)
From C/C++ point of view, it's legal for uninitialized memory to arbitrarily change between (undefined behavior) reads until it is written to.
While I doubt any actual OS would modify the page in this manner after first read access, a C/C++ compiler can still return arbitrary (even random) values when reading from uninitialized memory. It doesn't even need to actually read from the memory proven to be uninitialized.