cs375 p. 170

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Initializing BSS Storage

A block of data can be declared in assembly language with a BSS (Block Starting with Symbol) pseudo-op:


bigarray:    bss      8000000

Similar data can be declared in high-level languages:


double bigarray[1000][1000];

Instead of representing such a large block as a memory image, the block is represented in the absolute file by giving its starting address, size, and the initial value. The loader will fill the memory area with the initial value.

Although the loader might not have to initialize BSS areas, there are several advantages to doing so:

It prevents security problems: otherwise, a program can see the previous program's data.
It makes a program run the same way each time. Otherwise, a program might work if the initial value is lucky, but not work for other values.
It allows detection of use of uninitialized data if the array is filled with the SNaN (Signaling Not a Number) value.