MIPS: memset.S: Add comments to fault fixup handlers (6312455a) · Commits · 戴 / test

It is not immediately obvious what the expected inputs to these fault handlers is and how they calculate the number of unset bytes. Having stared deeply at this in order to fix some corner cases, add some comments to assist those who follow. Signed-off-by:

Matt Redfearn <matt.redfearn@mips.com> Signed-off-by:

Paul Burton <paul.burton@mips.com> Patchwork: https://patchwork.linux-mips.org/patch/19339/ Cc: James Hogan <jhogan@kernel.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: <linux-mips@linux-mips.org> Cc: <linux-kernel@vger.kernel.org>

arch/mips/lib/memset.S

+18 −0

Original line number	Diff line number	Diff line
		@@ -232,16 +232,25 @@

		#ifdef CONFIG_CPU_MIPSR6
		.Lbyte_fixup\@:
		/*
		* unset_bytes = (#bytes - (#unaligned bytes)) - (-#unaligned bytes remaining + 1) + 1
		* a2 = a2 - t0 + 1
		*/
		PTR_SUBU a2, t0
		jr ra
		PTR_ADDIU a2, 1
		#endif /* CONFIG_CPU_MIPSR6 */

		.Lfirst_fixup\@:
		/* unset_bytes already in a2 */
		jr ra
		nop

		.Lfwd_fixup\@:
		/*
		* unset_bytes = partial_start_addr + #bytes - fault_addr
		* a2 = t1 + (a2 & 3f) - $28->task->BUADDR
		*/
		PTR_L t0, TI_TASK($28)
		andi a2, 0x3f
		LONG_L t0, THREAD_BUADDR(t0)
		@@ -250,6 +259,10 @@
		LONG_SUBU a2, t0

		.Lpartial_fixup\@:
		/*
		* unset_bytes = partial_end_addr + #bytes - fault_addr
		* a2 = a0 + (a2 & STORMASK) - $28->task->BUADDR
		*/
		PTR_L t0, TI_TASK($28)
		andi a2, STORMASK
		LONG_L t0, THREAD_BUADDR(t0)
		@@ -258,10 +271,15 @@
		LONG_SUBU a2, t0

		.Llast_fixup\@:
		/* unset_bytes already in a2 */
		jr ra
		nop

		.Lsmall_fixup\@:
		/*
		* unset_bytes = end_addr - current_addr + 1
		* a2 = t1 - a0 + 1
		*/
		PTR_SUBU a2, t1, a0
		jr ra
		PTR_ADDIU a2, 1

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