Messages in this thread | | | Date | Wed, 9 Jul 2003 12:08:23 -0400 | From | Kurt Wall <> | Subject | Re: modutils-2.3.15 'insmod' |
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Quoth Richard B. Johnson: > > modutils-2.3.15, and probably later, has a bug that can prevent > modules from being loaded from initrd, this results in not > being able to mount a root file-system. The bug assumes that > malloc() will return a valid pointer when given an allocation > size of zero.
This isn't a bug. The standard allow returning a non-null pointer for malloc(0).
> When there are no modules loaded, insmod scans for modules > and allocates data using its xmalloc() based upon the number > of modules found. If the number was 0, it attempts to allocate > 0 bytes (0 times the size of a structure). If malloc() returns > NULL (and it can, probably should), xmalloc() will write an > "out of memory" diagnostic and call exit(). > > The most recent `man` pages that RH 9.0 distributes states that > malloc() can return either NULL of a pointer that is valid for > free(). This, of course, depends upon the 'C' runtime library's > malloc() implementation.
Perhaps, but IIRC, the rationale in the GNU C library was that existing programs assume malloc(0) != 0, which allows you to call realloc on the pointer. Returning NULL only makes sense if the malloc() call fails.
> It is likely that malloc(0) returning a valid pointer is a bug > that has prevented this problem from being observed. Such a > bug in malloc() is probably necessary to keep legacy software
Not a bug. Bad design perhaps, but not a bug.
> running, but new software shouldn't use such atrocious side-effects. > An allocation of zero needs to be discovered and fixed early > in code design.
Kurt -- If you sit down at a poker game and don't see a sucker, get up. You're the sucker. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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