June 2, 2021 9:08 AM, "Kent Mcleod" <kent.mcleo...@gmail.com> wrote:
> On Thu, May 20, 2021 at 6:13 AM Ben Fiedler <s...@bfiedler.ch> wrote: > >> Hello everyone, >> >> I've recently found an interesting bug that only occurs when compiling in >> release mode. >> >> Use of the ZF_LOG library (for normal log output) leads to syscalls being >> made when the >> capdl-loader runs. >> These are invoked via musllibc's __stdio_write, which relies on __sysinfo >> being set correctly for >> syscalls to >> work. When compiling with RELEASE=OFF this works fine, however when >> compiling with RELEASE=ON, >> __sysinfo is >> not set (yet?), and subsequently leads to an illegal prefetch exception when >> __stdio_write tries to >> invoke >> a syscall. >> >> Setting __sysinfo to sel4_vsyscall using gdb during runtime fixes this. I >> don't really know the >> correct >> place to fix this in the code, but I hope that you can provide some hints on >> where to fix this bug. > > If you look in the CMake file capdl-loader-app/helpers.cmake you will > see that libsel4muslcsys is only linked into the capdl-loader-app > under debug builds. This library implements the registration of a set > of syscalls under __sysinfo and any printing would need to go through > that. Thus, the capdl-loader-app doesn't support log output via > ZF_LOG while RELEASE=ON. > > RELEASE=ON essentially does 2 things currently: Turn off kernel debug > syscalls, and turn up optimization levels for the compiler. The > printing in the capdl-loader-app needs the seL4_DebugPutChar syscall, > so you would still need that syscall to turn on printing. Ah that makes sense. I've worked around this issue by selectively enabling printing only in the files I need to (using #define ZF_LOG_LEVEL). > If you wanted to add printing when RELEASE=ON then you would need to > link libsel4muslcsys unconditionally, and edit main.c to call > init_bootinfo also, and you would need to also set KernelPrinting=ON. I'll keep this in mind for further debugging, thanks! _______________________________________________ Devel mailing list -- devel@sel4.systems To unsubscribe send an email to devel-leave@sel4.systems
