[Bug ld/12376] File offsets for PT_LOAD segments and resulting inequivalent memory aliases

[dave at hiauly1 dot hia.nrc.ca]

http://sourceware.org/bugzilla/show_bug.cgi?id=12376

--- Comment #7 from dave at hiauly1 dot hia.nrc.ca <dave at hiauly1 dot 
hia.nrc.ca> 2011-02-14 14:51:27 UTC ---
> If they are the same page, doesn't that mean your maxpagesize is wildly
> incorrect?  You must have maxpagesize at least as large as a memory page.

maxpagesize is set to 0x1000 which is the standard page size for parisc
linux.

The issue is not the virtual addresses of the page but the placement
of the loadable segments in the file.  These segments are mmap'd from
the file to physical memory.  Although the pages could be different
in memory, they are not.

The issue can be seen by looking at the mappings for a trivial program like:

int main () { return 0 }

For the the main executable, there is only one file page for text
and data.  Run program under gdb with a break on main.  Then inspect
the mappings.

The two mappings could be made equivalent, but this messes up shared
library support.

The hardware can support larger page sizes, but as far as I know nobody
uses them on linux.  There was some effort to provide support for larger
page sizes in the linux kernel but I don't believe the cache flush and
TLB support is complete.

Possibly, ELF_COMMONPAGESIZE should be defined and ELF_MAXPAGESIZE
increased to the linux kernel maximum.

Dave

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