Hi all,
I have a computer with 4GB with FedoraCore3 installed, and wrote this
program that allocates a >2G array:
int main(int,char**) {
unsigned int size = (unsigned int)2 * 1024 *1024 *1024 + 1000;
char *p;
p = malloc(size);
if (p != NULL)
printf("OK\n");
else
printf("Bad\n");
}
Using the kernel supplied with FC the buffer is allocated. When I use a
kernel I compile malloc returns NULL.
I am aware of the high-mem support and I tried it set to 4G and 64G.
Furthermore, when I compile a kernel with the config file given by FC
(linux-2.6.5-1.358/configs/kernel-2.6.5-i* ) it
doesn't work (although the kernel should be configured the same).
Obviously this has something to do with the way I build the kernel,
since when I use the kernel supplied with FC3 it works well.
I also tried to copy a good kernel I compiled on another machine (together
with its modules) and this one doesn't work as well, although on the
original machine it worked.
Another strange thing:
Using ldd on the "bad" machine I get:
[root@host1 root]# ldd test_hi_mem
linux-gate.so.1 => (0x00280000)
libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x4e056000)
libm.so.6 => /lib/tls/libm.so.6 (0x4d316000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x4deb8000)
libc.so.6 => /lib/tls/libc.so.6 (0x4d1f3000)
/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x4d1da000)
while on the "good" machine I get:
[root@host2 root]# ldd test_high_mem
linux-gate.so.1 => (0xffffe000)
libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x072d7000)
libm.so.6 => /lib/tls/libm.so.6 (0x0079c000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x005f3000)
libc.so.6 => /lib/tls/libc.so.6 (0x00679000)
/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00660000)
This suggests that the "bad" machine puts the libraries in the middle of
the address space. But then I do not understand how any kernel can
allocate 2G.
Any suggestions?
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