git: b49a0db6628e - main - Revert "amd64: implement strlen in assembly"

[Mateusz Guzik]

The branch main has been updated by mjg:

URL: https://cgit.FreeBSD.org/src/commit/?id=b49a0db6628e6f953504ebc8712ed582471ccd05

commit b49a0db6628e6f953504ebc8712ed582471ccd05
Author:     Mateusz Guzik <mjg at FreeBSD.org>
AuthorDate: 2021-02-09 15:18:58 +0000
Commit:     Mateusz Guzik <mjg at FreeBSD.org>
CommitDate: 2021-02-09 15:23:18 +0000

    Revert "amd64: implement strlen in assembly"
    
    This reverts commit af366d353b84bdc4e730f0fc563853abc338271c.
    
    Trips over '\xa4' byte and terminates early, as found in
    lib/libc/gen/setdomainname_test:setdomainname_basic testcase
    
    However, keep moving libkern/strlen.c out of conf/files.
    
    Reported by:    lwhsu
---
 sys/amd64/amd64/support.S | 66 -----------------------------------------------
 sys/conf/files.amd64      |  1 +
 2 files changed, 1 insertion(+), 66 deletions(-)

diff --git a/sys/amd64/amd64/support.S b/sys/amd64/amd64/support.S
index a059b520c5d5..b623fba277db 100644
--- a/sys/amd64/amd64/support.S
+++ b/sys/amd64/amd64/support.S
@@ -697,72 +697,6 @@ ENTRY(fillw)
 	ret
 END(fillw)
 
-/*
- * strlen(string)
- *	  %rdi
- *
- * Uses the ((x - 0x01....01) & ~x & 0x80....80) trick.
- *
- * 0x01....01 is replaced with 0x0 - 0x01....01 so that it can be added
- * with leaq.
- *
- * For a description see either:
- * - "Hacker's Delight" by Henry S. Warren, Jr.
- * - "Optimizing subroutines in assembly language: An optimization guide for x86 platforms"
- *   by Agner Fog
- *
- * The latter contains a 32-bit variant of the same algorithm coded in assembly for i386.
- */
-ENTRY(strlen)
-	PUSH_FRAME_POINTER
-	movabsq	$0xfefefefefefefeff,%r8
-	movabsq	$0x8080808080808080,%r9
-
-	movq	%rdi,%r10
-	movq	%rdi,%rcx
-	testb	$7,%dil
-	jz	2f
-
-	/*
-	 * Handle misaligned reads: align to 8 and fill
-	 * the spurious bytes.
-	 */
-	andq	$~7,%rdi
-	movq	(%rdi),%r11
-	shlq	$3,%rcx
-	movq	$-1,%rdx
-	shlq	%cl,%rdx
-	notq	%rdx
-	orq	%rdx,%r11
-
-	leaq	(%r11,%r8),%rcx
-	notq	%r11
-	andq	%r11,%rcx
-	andq	%r9,%rcx
-	jnz	3f
-
-	/*
-	 * Main loop.
-	 */
-	ALIGN_TEXT
-1:
-	leaq	8(%rdi),%rdi
-2:
-	movq	(%rdi),%r11
-	leaq	(%r11,%r8),%rcx
-	notq	%r11
-	andq	%rcx,%r11
-	andq	%r9,%rcx
-	jz	1b
-3:
-	bsfq	%rcx,%rcx
-	shrq	$3,%rcx
-	leaq	(%rcx,%rdi),%rax
-	subq	%r10,%rax
-	POP_FRAME_POINTER
-	ret
-END(strlen)
-
 /*****************************************************************************/
 /* copyout and fubyte family                                                 */
 /*****************************************************************************/
diff --git a/sys/conf/files.amd64 b/sys/conf/files.amd64
index 395f501198f8..98a78a8b1ef9 100644
--- a/sys/conf/files.amd64
+++ b/sys/conf/files.amd64
@@ -390,6 +390,7 @@ isa/syscons_isa.c		optional	sc
 isa/vga_isa.c			optional	vga
 kern/imgact_aout.c		optional compat_aout
 kern/link_elf_obj.c		standard
+libkern/strlen.c		standard
 #
 # IA32 binary support
 #