From: Ard Biesheuvel
mainline inclusion
from mainline-v5.13-rc1
commit 4c4dcd3541f8
category: bugfix
issue: #I3ZXZF
CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
-----------------------------------------------
The AArch64 asm syntax has this slightly tedious property that the names
used in mnemonics to refer to registers depend on whether the opcode in
question targets the entire 64-bits (xN), or only the least significant
8, 16 or 32 bits (wN). When writing parameterized code such as macros,
this can be annoying, as macro arguments don't lend themselves to
indexed lookups, and so generating a reference to wN in a macro that
receives xN as an argument is problematic.
For instance, an upcoming patch that modifies the implementation of the
cond_yield macro to be able to refer to 32-bit registers would need to
modify invocations such as
cond_yield 3f, x8
to
cond_yield 3f, 8
so that the second argument can be token pasted after x or w to emit the
correct register reference. Unfortunately, this interferes with the self
documenting nature of the first example, where the second argument is
obviously a register, whereas in the second example, one would need to
go and look at the code to find out what '8' means.
So let's fix this by defining wxN aliases for all xN registers, which
resolve to the 32-bit alias of each respective 64-bit register. This
allows the macro implementation to paste the xN reference after a w to
obtain the correct register name.
Signed-off-by: Ard Biesheuvel
Acked-by: Will Deacon
Link: https://lore.kernel.org/r/20210302090118.30666-3-ardb@kernel.org
Signed-off-by: Catalin Marinas
Signed-off-by: Wei Li
Reviewed-by: Jason Yan
Reviewed-by: Hanjun Guo
Signed-off-by: Chen Jun
Signed-off-by: Yu Changchun
---
arch/arm64/include/asm/assembler.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 2746aaa61438..21d679bf1e55 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -23,6 +23,14 @@
#include
#include
+ /*
+ * Provide a wxN alias for each wN register so what we can paste a xN
+ * reference after a 'w' to obtain the 32-bit version.
+ */
+ .irp n,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30
+ wx\n .req w\n
+ .endr
+
.macro save_and_disable_daif, flags
mrs \flags, daif
msr daifset, #0xf
--
2.22.0
