[Barrelfish-users] Maybe a Bug of modify_flags

[jhshi at cs.hku.hk]

Hi,

For some reason, I need to work on x86_32 instead of x86_64. And I  
found that x86_32's pmap->f.modify_flags is NYI. So I ported it from  
x86_64, as described by my previous email (link). But then I found  
that the port won't work properly. Personally, I don't think the  
problem lies in the porting but in the modify_flags itself.

Here is my test case workflow:

First allocate two pages using frame_alloc and map them at some "safe"  
virtual address as read-only using pmap->f.map. Then fill the two  
pages with different content. Since they are read-only, page faults  
will occur when filling. I catch them and map the fault page as  
read-write using pmap->f.modify_flags in the fault handler. But then I  
found that the two page's content are identical, which is not supposed  
to be.

Then I found that if I allocate one frame for each page, instead of  
one monolithic frame, everything is fine.

I've summarized my test in the attached C file, which should be  
compiled and run under x86_32. Apology for not being able to test it  
under X86_64 since I encounter some weird errors when compiling arch  
x86_64. But if you substitute all the X86_32 to X86_64 in the test  
file, it should work under x86_64 as well.

However, if the test goes all fine under x86_64, then please give some  
hint about why its x86_32's port would fail.

Thanks in advance!

Regards,
Jinghao
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