Re: GDB testsuite: »Memory at address 0 is possibly executable«

[Justus Winter]

Quoting Samuel Thibault (2014-09-13 01:39:05)
> So it seems we need what is not actually documented, i.e. a vm_map
> with anywhere=1, but which takes into account the suggested address.
> I'm fine with officially supporting that, we just need to fix the
> documentation,

I'm sorry, I'm lost.  What other interpretation of 'anywhere' is
there?  And since you aligned the semantic of vm_maps 'anywhere' with
'vm_allocate', then it follows that the current interpretation is
either wrong or right for both functions, no?

I just looked at mmap(2).  If one specifies a non-NULL address, Linux
will use the address as hint.  If it is NULL, and MAP_FIXED is not
given, Linux choses a suitable address.  It isn't explicitly stated,
but I'm pretty sure the Linux kernel doesn't consider the zero page a
suitable place.

> and fix all places which weren't aware of this behavior (there are
> very few).

How would I chose a suitable address?  E.g. ext2fs/dir.c initializes
the address to 0, but then vm_map_enter would set it to
map->min_offset anyway (or map->min_offset is 0), which is the same as
vm_map_min(map).

Justus