As ARM64 is entering enterprise world, machines can not be stopped for some critical enterprise production environment, that is, live patch as one of the RAS features is increasing more important for ARM64 arch now.
Now, the mainstream live patch implementation which has been merged in Linux kernel (x86/s390) is based on the 'ftrace with regs' feature, and this feature needs the help of gcc. This patch proposes a generic solution for arm64 gcc which called mfentry, following the example of x86, mips, s390, etc. and on these archs, this feature has been used to implement the ftrace feature 'ftrace with regs' to support live patch. By now, there is an another solution from linaro [1], which proposes to implement a new option -fprolog-pad=N that generate a pad of N nops at the beginning of each function. This solution is a arch-independent way for gcc, but there may be some limitations which have not been recognized for Linux kernel to adapt to this solution besides the discussion on [2], typically for powerpc archs. Furthermore I think there are no good reasons to promote the other archs (such as x86) which have implemented the feature 'ftrace with regs' to replace the current method with the new option, which may bring heavily target-dependent code adaption, as a result it becomes a arm64 dedicated solution, leaving kernel with two different forms of implementation. [1] https://gcc.gnu.org/ml/gcc/2015-10/msg00090.html [2] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-January/401854.html Jiangjiji (1): [AArch64] support -mfentry feature for arm64 gcc/config/aarch64/aarch64.c | 23 +++++++++++++++++++++++ gcc/config/aarch64/aarch64.h | 13 ++++++++----- gcc/config/aarch64/aarch64.opt | 4 ++++ 3 files changed, 35 insertions(+), 5 deletions(-)
