ARM: ftrace: use ADD not POP to counter PUSH at entry

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The compiler emitted hook used for ftrace consists of a PUSH {LR} to
preserve the link register, followed by a branch-and-link (BL) to
__gnu_mount_nc. Dynamic ftrace patches away the latter to turn the
combined sequence into a NOP, using a POP {LR} instruction.

This is not necessary, since the link register does not get clobbered in
this case, and simply adding #4 to the stack pointer is sufficient, and
avoids a memory access that may take a few cycles to resolve depending
on the micro-architecture.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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Ard Biesheuvel 2021-12-08 08:42:03 +01:00

parent dd88b03ff0

commit ad1c2f39fd

2 changed files with 14 additions and 3 deletions

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2

arch/arm/kernel/entry-ftrace.S

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15

arch/arm/kernel/ftrace.c

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