[PATCH 0/3] modpost: work around unaligned data access

[Masahiro Yamada]

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.



Masahiro Yamada (3):
  modpost: fix the missed iteration for the max bit in do_input()
  modpost: refactor do_vmbus_entry()
  modpost: work around unaligned data access error

 scripts/mod/file2alias.c | 36 +++++++++++++++++-------------------
 scripts/mod/modpost.c    | 24 ++++++++++++------------
 scripts/mod/modpost.h    | 14 ++++++++++++++
 3 files changed, 43 insertions(+), 31 deletions(-)

-- 
2.43.0