在 2022/6/18 20:40, Mark Rutland 写道:

On Sat, Jun 18, 2022 at 04:42:06PM +0800, Tong Tiangen wrote:

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diff --git a/arch/arm64/include/asm/asm-extable.h

b/arch/arm64/include/asm/asm-extable.h
index 56ebe183e78b..9c94ac1f082c 100644

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

@@ -28,6 +28,14 @@
       __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_FIXUP, 0)
       .endm
+/*
+ * Create an exception table entry for uaccess `insn`, which

will branch to `fixup`
+ * when an unhandled fault is taken.
+ * ex->data = ~0 means both reg_err and reg_zero is set to wzr(x31).
+ */
+    .macro          _asm_extable_uaccess, insn, fixup
+    __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_UACCESS_ERR_ZERO, ~0)
+    .endm

I'm not too keen on using `~0` here, since that also sets other bits
in the
data field, and its somewhat opaque.

How painful is it to generate the data fields as with the C version
of this
macro, so that we can pass in wzr explciitly for the two sub-fields?

Other than that, this looks good to me.

Thanks,
Mark.

ok, will fix next version.

Thanks,
Tong.

I tried to using data filelds as with C version, but here assembly code we
can not using operator such as << and |, if we use lsl and orr instructions,
the gpr will be occupied.

So how about using 0x3ff directly here? it means err register and zero
register both set to x31.

I had a go at implementing this, and it seems simple enough. Please see:

   https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/extable/asm-uaccess

I made the following modifications, and the other parts are based on 
your implementation:

arch/arm64/include/asm/asm-extable.h
[...]
.macro          _asm_extable_uaccess, insn, fixup
_ASM_EXTABLE_UACCESS(\insn, \fixup)
.endm
[...]


The following errors are reported during compilation:
[...]
arch/arm64/lib/clear_user.S:45: Error: invalid operands (*ABS* and *UND* 
sections) for `<<'
[...]

"<<" is invalid operands in assembly, is there something wrong with me?

Thanks,
Tong.

Mark.

.