diff mbox series

[v7,16/17] arm64: disable recordmcount with DYNAMIC_FTRACE_WITH_REGS

Message ID 20201118220731.925424-17-samitolvanen@google.com (mailing list archive)
State Superseded
Headers show
Series Add support for Clang LTO | expand

Commit Message

Sami Tolvanen Nov. 18, 2020, 10:07 p.m. UTC
DYNAMIC_FTRACE_WITH_REGS uses -fpatchable-function-entry, which makes
running recordmcount unnecessary as there are no mcount calls in object
files, and __mcount_loc doesn't need to be generated.

While there's normally no harm in running recordmcount even when it's
not strictly needed, this won't work with LTO as we have LLVM bitcode
instead of ELF objects.

This change selects FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY, which
disables recordmcount when patchable function entries are used instead.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 arch/arm64/Kconfig | 2 ++
 1 file changed, 2 insertions(+)

Comments

Will Deacon Nov. 30, 2020, 11:59 a.m. UTC | #1
On Wed, Nov 18, 2020 at 02:07:30PM -0800, Sami Tolvanen wrote:
> DYNAMIC_FTRACE_WITH_REGS uses -fpatchable-function-entry, which makes
> running recordmcount unnecessary as there are no mcount calls in object
> files, and __mcount_loc doesn't need to be generated.
> 
> While there's normally no harm in running recordmcount even when it's
> not strictly needed, this won't work with LTO as we have LLVM bitcode
> instead of ELF objects.
> 
> This change selects FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY, which
> disables recordmcount when patchable function entries are used instead.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
>  arch/arm64/Kconfig | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 1515f6f153a0..c7f07978f5b6 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -158,6 +158,8 @@ config ARM64
>  	select HAVE_DYNAMIC_FTRACE
>  	select HAVE_DYNAMIC_FTRACE_WITH_REGS \
>  		if $(cc-option,-fpatchable-function-entry=2)
> +	select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \
> +		if DYNAMIC_FTRACE_WITH_REGS

I don't really understand why this is in the arch header file, rather
than have the core code check for "fpatchable-function-entry=2" and expose
a CC_HAS_PATCHABLE_FUNCTION_ENTRY, but in the interest of making some
progress on this series:

Acked-by: Will Deacon <will@kernel.org>

Will
diff mbox series

Patch

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1515f6f153a0..c7f07978f5b6 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -158,6 +158,8 @@  config ARM64
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS \
 		if $(cc-option,-fpatchable-function-entry=2)
+	select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \
+		if DYNAMIC_FTRACE_WITH_REGS
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS
 	select HAVE_FAST_GUP
 	select HAVE_FTRACE_MCOUNT_RECORD