(no subject)

serguei.patchkovskii at sympatico.ca serguei.patchkovskii at sympatico.ca
Wed Oct 22 10:05:38 EDT 2003


> Any IA-32 compiler can create code and run on Opterons. Of course,
> 32-bit executables don't get the extra memory either, even when running
> on a 64-bit OS

Not true. A 32-bit binary running on x86-64 Linux has access to full 32-bit
address
space. When I run a very simple 32-bit Fortran program, I see program itself
mapped at very low addresses; the shaped libraries get mapped at 1Gbyte
mark,
while the stack grows down from 4Gbyte mark. On an x86 Linux, the upper
1Gbyte
(but this depends on the kernel options) is taken by the kernel address
space.

What this means in practice, is that on an x86 Linux, I can allocate at most
2.5Gbytes of memory for my data without resorting to ugly tricks; in 32-bit
mode of x86-64 Linux, this goes up to about 3.5Gbytes - enough to make a
difference in some cases.

Serguei


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