Re: Stange gcc 3.3 bug on Linux/ia64

[Zack Weinberg <zack at codesourcery dot com>]

"H. J. Lu" <hjl@lucon.org> writes:

> On Tue, Jul 01, 2003 at 11:19:44PM -0700, Zack Weinberg wrote:
>> "H. J. Lu" <hjl@lucon.org> writes:
>> 
>> > I have a very strange gcc 3.3 bug on Linux/ia64. At random, I got
>> > bootstrap failure:
>> [...]
>> 
>> Interesting bug, but the patch you sent is fixing a non-bug, and one
>> that could not cause the problem you see even if it were a bug.  You
>> should be looking at the scheduler or the register allocator.
>> 
>> cpplib in 3.3 relies on documented and standardized behavior of mmap,
>> which valgrind deliberately does not support because use of it is
>> usually a bug.  Specifically, the memory between the end of a file
>> that's been mmapped into memory, and the nearest higher page boundary,
>> is guaranteed to be zero-filled by the kernel.  (In 3.4 we are no
>
> One mmap test in gcc 3.3 failed on Linux/ia64:
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3163

That is anonymous mmap, which has nothing whatsoever to do with file
mmap, and that test was broken anyway.

Zero-filling to the nearest page boundary is guaranteed by SUS, and to
do anything else is a security hole.  (well, technically you could
fill with truly random data to a page boundary, but why waste entropy
like that?)

And if the kernel isn't holding up its end, what you would get is a
syntax error, probably "stray '\xNN' in program".

zw