While build nanoBench kernel module in Ubuntu 22.04, gcc is with
-mfunction-return=thunk-extern as default option. According to chapter
6.1.1 JMP2RET in the following reference:
https://www.amd.com/system/files/documents/\
technical-guidance-for-mitigating-branch-type-confusion.pdf
all 'ret' instructions are consolidated into a single piece of code.
Instead of functions ending with a 'ret' instruction, they instead end
with "jump __x86_return_thunk".
Since a 'jmp' instruction is provided instead of 'ret' at the end of
each function, it cause functions like create_runtime_code() copy much
more assembler code into runtime_code memory than it should during
runtime. Memory protection fault happens finally while running.
To address the above issue, option -mfunction-return=keep is provided
for kernel mode to overwrite the gcc default behavior in Ubuntu 22.04.
This can ensure function has 'ret' instruction generated.
Signed-off-by: Cathy Zhang <cathy.zhang@intel.com>
