arm64: ftrace: forbid CALL_OPS with CC_OPTIMIZE_FOR_SIZE

Florian reports that when building with CONFIG_CC_OPTIMIZE_FOR_SIZE=y,
he sees "Misaligned patch-site" warnings at boot, e.g.

| Misaligned patch-site bcm2836_arm_irqchip_handle_irq+0x0/0x88
| WARNING: CPU: 0 PID: 0 at arch/arm64/kernel/ftrace.c:120 ftrace_call_adjust+0x4c/0x70

This is because GCC will silently ignore `-falign-functions=N` when
passed `-Os`, resulting in functions not being aligned as we expect.
This is a known issue, and to account for this we modified the kernel to
avoid `-Os` generally. Unfortunately we forgot to account for
CONFIG_CC_OPTIMIZE_FOR_SIZE.

Forbid the use of CALL_OPS with CONFIG_CC_OPTIMIZE_FOR_SIZE=y to prevent
this issue. All exising ftrace features will work as before, though
without the performance benefit of CALL_OPS.

Reported-by: Florian Fainelli <[email protected]>
Link: http://lore.kernel.org/linux-arm-kernel/[email protected]
Signed-off-by: Mark Rutland <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Stefan Wahren <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Will Deacon <[email protected]>
Tested-by: Florian Fainelli <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

Author: mrutland-arm

arch/arm64/Kconfig

@@ -188,7 +188,8 @@ config ARM64
 	select HAVE_DYNAMIC_FTRACE_WITH_ARGS \
 		if $(cc-option,-fpatchable-function-entry=2)
 	select HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS \
-		if (DYNAMIC_FTRACE_WITH_ARGS && !CFI_CLANG)
+		if (DYNAMIC_FTRACE_WITH_ARGS && !CFI_CLANG && \
+		    !CC_OPTIMIZE_FOR_SIZE)
 	select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \
 		if DYNAMIC_FTRACE_WITH_ARGS
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS