On Sat, Apr 13, 2013 at 4:59 AM, Terry Hsu <terry.sh...@gmail.com> wrote: > > On Fri, Apr 12, 2013 at 1:14 AM, Terry Hsu <terry.sh...@gmail.com> wrote: >> >> okay so I looked into the faultinfo structure and was able to obtain the >> faulting address, error code, and trap number(?). From my understanding the >> error code is the bottom 3 bits of the exception code. But I see error code >> "20" sometimes and do not what it means. > > > According to p.6-55 in Intel® 64 and IA-32 Architectures Software > Developer’s Manual, Volume 3: System Programming Guide, the lower 5 bits are > Present, Read/Write, User/supervisor, RSVD, and Instruction/Data bit > respectively. So error code 20 means the fault is caused by an instruction > read to a non-present page in user mode. > > I found the the reason why the fault cannot be fixed by UML. It is probably > because UML puts the faultinfo in the wrong stub, since I changed the vm > area pointers of the child process, when the fault happens, UML incorrectly > finds its parent process's stub pages and puts the faultinfo in it. > Therefore when the child process tries to access its own skas stub and fix > the fault, it still cannot find the correct instruction pointers hence the > fault happens endlessly.
Can you share an example with us which triggers the issue? > Why does every process that runs in UML need its own stub for page fault > handling? It seems to me they could've shared the SIGSEGV signal handler and > the function that invokes mmap, munmap, mprotect. In this way only two pages > are needed for all the processes. > > I am not sure if I understand the whole thing correctly. Please correct me > if it's not right. We need a stub per process because the installs a mapping into the prozess (on the host size). As mmap() always operates on current, we need a way to make the prozess call mmap() itself. The stub does this. -- Thanks, //richard ------------------------------------------------------------------------------ Precog is a next-generation analytics platform capable of advanced analytics on semi-structured data. The platform includes APIs for building apps and a phenomenal toolset for data science. Developers can use our toolset for easy data analysis & visualization. Get a free account! http://www2.precog.com/precogplatform/slashdotnewsletter _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
