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| Author |
Message |
< Erlang bugs mailing list ~ win32sysinfo.c doesn't understand DWORDLONG is unsigned and |
| Guest |
 Posted: Thu Jan 28, 2010 5:40 pm |
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Guest
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void get_avail_mem_ext() {
char answer[512];
MEMORYSTATUSEX ms;
ms.dwLength=sizeof(MEMORYSTATUSEX);
GlobalMemoryStatusEx(&ms);
sprintf(answer,"%d %I64d %I64d %I64d %I64d %I64d %I64d\n",
ms.dwMemoryLoad,
ms.ullTotalPhys,
ms.ullAvailPhys,
ms.ullTotalPageFile,
ms.ullAvailPageFile,
ms.ullTotalVirtual,
ms.ullAvailVirtual
);
return_answer(answer);
/*
DWORD dwLength;
DWORD dwMemoryLoad;
DWORDLONG ullTotalPhys;
DWORDLONG ullAvailPhys;
DWORDLONG ullTotalPageFile;
DWORDLONG ullAvailPageFile;
DWORDLONG ullTotalVirtual;
DWORDLONG ullAvailVirtual;
*/
}
DWORD and DWORDLONG are unsigned and long. By printing with %I64d, you're
reinterpreting them as signed ints, leading to windows users with 4GB of
RAM being told they have negative amounts of RAM (or even 0). Eg:
$ cat foo.c
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
main()
{
uint64_t n = 4293308416;
printf("%I64d\n", n);
printf("%I64u\n", n);
printf("%I64lu\n", n);
return 0;
}
$ gcc -o foo foo.c && ./foo
-1658880
4293308416
4293308416
Elsewhere in win32sysinfo.c, there are %I64u format specifiers. It looks
like the only occurrence of %I64d is in the get_avail_mem_ext function.
Because they're long, I *think* they should be %I64lu. I think what's
happening is that the d makes it an int, thus the msb is set, hence the
negative answer. And indeed, setting n to 4294967297 (i.e. 2^32 + 1)
gives:
1
1
4294967297
Note that the above is running under a 64-bit Linux. I don't know if the
behaviour of %I64 is the same under Windows. I also don't know what size
an int is in a 32-bit application running on 64-bit windows. My C isn't
all that great. My reading is that the %I64 just says to use the system
locale, and to pad with whitespace up to 64 characters.
Matthew
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erlang-bugs (at) erlang.org
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