On Thu, Dec 26, 2024 at 1:27 AM John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx> wrote: > > Hi Masahiro, > > > The latest binutils stopped aligning section data in relocatable ELF. > > It saves small number of bytes that were previously inserted between > > sections. However, modpost crashes due to unaligned access: > > https://sourceware.org/bugzilla/show_bug.cgi?id=32435 > > https://sourceware.org/bugzilla/show_bug.cgi?id=32493 > > > > Similar to kernel space, unaligned data access in userspace can be > > problematic on some architectures. > > > > Simple example on ARM: > > > > $ CC=arm-linux-gnueabihf-gcc > > $ echo 'int foo(int *p) { return *p + *(p + 1); }' | ${CC} -O2 -x c - -c -o foo.o > > $ echo 'int foo(int *p); int main(void) { char str[16] = "helloworld"; return foo((int *)(str + 1)); }' | ${CC} -x c - -c -o main.o > > $ ${CC} -static -o unalign-test main.o foo.o > > $ qemu-armhf unalign-test > > qemu: uncaught target signal 7 (Bus error) - core dumped > > Bus error (core dumped) > > > > In this case, the 'ldrd' instruction causes a bus error due to an > > unaligned access. If the -O2 flag is omitted, this issue does not occur. > > > > To avoid potential unaligned access, use the get_unaligned() approach > > as seen in the kernel space. > > I have just applied this series against Linus' tree and I can confirm that it fixes the > unalignment access anymore on sparc64. There is no more "Bus error" and the build succeeds. > > Tested-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx> Thanks for the compile test. Loadable modules (*.ko files) are relocatable ELF. So, there is no alignment in *.ko files any more if the latest binutils is used. Just in case, I did run-tests for arm and arm64. Even if there is no alignment in *.ko files, I confirmed that the kernel can load modules. If you have time, please run-test and double-check loadable modules are working. -- Best Regards Masahiro Yamada
