Re: [PATCH v3 2/2] arm64: Unconditionally override SYM_FUNC macros

On Mon, Dec 13, 2021 at 07:21:25PM +0000, Mark Brown wrote:

On Mon, Dec 13, 2021 at 06:46:54PM +0000, Will Deacon wrote:

quoted

On Wed, Dec 08, 2021 at 04:08:19PM +0000, Mark Brown wrote:

quoted

quoted

--- a/arch/arm64/include/asm/linkage.h
+++ b/arch/arm64/include/asm/linkage.h

@@ -8,10 +8,18 @@
 
 #define BTI_C bti c ;
 
+#else
+
+#define BTI_C
+
+#endif

quoted

Why do we need this hunk? Having the hint instruction should be fine, no?

We could unconditionally insert the hint but that would be a step back
from what we currently have and would mean that hand written assembly
would be that little bit worse than what the compiler outputs.  If this
had been causing us issues I could see simplifying but I'm not aware of
any - the issues I'm aware of have been due to not adding the landing
pads in SYM_CODE, not SYM_FUNC.

I don't have a strong opinion here, so whatever you like. I just tend to
think that most people will have BTI enabled and there's something to be
said for having an instruction always emitted when you have a token in
assembly code.

Will

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