Srinivas Ramanan <srinivas.ramanan@gmail.com> wrote:

Hi all, This is an interview question. "What is the implication of mapping BSS to the Virtual Memory Segment 0?"

I was not able to find the answer from web. So posting here. thanks, srinivas

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As a guess, Linux kernel developers leverage the fact that low address values are illegal, thus a pointer handling error that generates a low address value triggers a trap which allows the programmer to know he screwed up. Using virtual memory segment zero makes those valid addresses and thus programming errors are more likely to slip through un-noticed. HTH Greg -- Sent from my Android phone with K-9 Mail. Please excuse my brevity.

On Mon, Aug 27, 2012 at 2:01 AM, Srinivas Ramanan < srinivas.ramanan@gmail.com> wrote:

Hi all, This is an interview question. "What is the implication of mapping BSS to the Virtual Memory Segment 0?"

I was not able to find the answer from web. So posting here. thanks, srinivas

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Hi, The bss section typically includes all uninitialized variables declared with the static keyword. The zero page which is a copy-on-write page that reads as zero is used to map the BSS segment. Any process referencing the zero page sees the page filled with zeos and if it tries to writes to the page, it ends up modifying a private copy. (LDD ch15. page 429) Mulyadi, Why it will generate a page fault later when process will tries to reference it, while it already has mapped with the zero page? Sorry if i am wrong anywhere. Ritesh