Machine: MIPS32 R2 Big Endian (interAptiv (multi)) While testing MIPS with LLVM, I found a weird and very rare bug with MIPS relocs that LLVM emits into kernel modules. It happens on both 11.0.0 and latest git snapshot and applies, as I can see, only to references to static symbols. When the kernel loads the module, it allocates a space for every section and then manually apply the relocations relative to the new address. Let's say we have a function phy_probe() in drivers/net/phy/libphy.ko. It's static and referenced only in phy_register_driver(), where it's used to fill callback pointer in a structure. The real function address after module loading is 0xc06c1444, that is observed in its ELF st_value field. There are two relocs related to this usage in phy_register_driver(): R_MIPS_HI16 refers to 0x3c010000 R_MIPS_LO16 refers to 0x24339444 The address of .text is 0xc06b8000. So the destination is calculated as follows: 0x00000000 from hi16; 0xffff9444 from lo16 (sign extend as it's always treated as signed); 0xc06b8000 from base. = 0xc06b1444. The value is lower than the real phy_probe() address (0xc06c1444) by 0x10000 and is lower than the base address of module's .text, so it's 100% incorrect. This results in: [ 2.204022] CPU 3 Unable to handle kernel paging request at virtual address c06b1444, epc == c06b1444, ra == 803f1090 The correct instructions should be: R_MIPS_HI16 0x3c010001 R_MIPS_LO16 0x24339444 so there'll be 0x00010000 from hi16. I tried to catch those bugs in arch/mips/kernel/module.c (by checking if the destination is lower than the base address, which should never happen), and seems like I have only 3 such places in libphy.ko (and one in nf_tables.ko). I don't think it should be handled somehow in mentioned source code as it would look rather ugly and may break kernels build with GNU stack, which seems to not produce such bad codes. If I should report this to any other resources, please let me know. I chose clang-built-linux and LKML as it may not happen with userland (didn't tried to catch). Thanks, Al
