[PATCH v2] arm: ARMv4 assembly compatibility

[PATCH v2] arm: ARMv4 assembly compatibility

[Sergei Antonov]

There is currently a problem that U-Boot can not work on ARMv4
because assembly imlementations of memcpy() and some other functions
use "bx lr" instruction that is not available on ARMv4 ("mov pc, lr"
should be used instead).

A working preprocessor-based solution to this problem is found in
arch/arm/lib/relocate.S. Move it to the "ret" macro in
arch/arm/include/asm/assembler.h and change all "bx lr" code
to "ret lr" in functions that may run on ARMv4. Linux source code
deals with this problem in the same manner.

v1 -> v2:
Comment update. Pointed out by Andre Przywara.

Signed-off-by: Sergei Antonov <saproj@gmail.com>
CC: Samuel Holland <samuel@sholland.org>
CC: Ye Li <ye.li@nxp.com>
CC: Simon Glass <sjg@chromium.org>
CC: Andre Przywara <andre.przywara@arm.com>
CC: Marek Vasut <marex@denx.de>
CC: Sean Anderson <sean.anderson@seco.com>
CC: Tom Rini <trini@konsulko.com>
---
 arch/arm/include/asm/assembler.h | 10 ++++++++--
 arch/arm/lib/lib1funcs.S         |  8 ++++----
 arch/arm/lib/memcpy.S            |  6 +++---
 arch/arm/lib/relocate.S          | 10 ++--------
 arch/arm/lib/setjmp.S            |  4 ++--
 5 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index b14691858601..8d42ef4823e9 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -58,16 +58,22 @@
 #endif
 
 /*
- * We only support cores that support at least Thumb-1 and thus we use
- * 'bx lr'
+ * Use 'bx lr' everywhere except ARMv4 (without 'T') where only 'mov pc, lr'
+ * works
  */
 	.irp	c,,eq,ne,cs,cc,mi,pl,vs,vc,hi,ls,ge,lt,gt,le,hs,lo
 	.macro	ret\c, reg
+
+	/* ARMv4- don't know bx lr but the assembler fails to see that */
+#ifdef __ARM_ARCH_4__
+	mov\c	pc, \reg
+#else
 	.ifeqs	"\reg", "lr"
 	bx\c	\reg
 	.else
 	mov\c	pc, \reg
 	.endif
+#endif
 	.endm
 	.endr
 
diff --git a/arch/arm/lib/lib1funcs.S b/arch/arm/lib/lib1funcs.S
index 700eee5fbbe0..7ff4446dd644 100644
--- a/arch/arm/lib/lib1funcs.S
+++ b/arch/arm/lib/lib1funcs.S
@@ -377,7 +377,7 @@ ENTRY(__gnu_thumb1_case_sqi)
 	lsls	r1, r1, #1
 	add	lr, lr, r1
 	pop	{r1}
-	bx	lr
+	ret	lr
 ENDPROC(__gnu_thumb1_case_sqi)
 .popsection
 
@@ -391,7 +391,7 @@ ENTRY(__gnu_thumb1_case_uqi)
 	lsls	r1, r1, #1
 	add	lr, lr, r1
 	pop	{r1}
-	bx	lr
+	ret	lr
 ENDPROC(__gnu_thumb1_case_uqi)
 .popsection
 
@@ -406,7 +406,7 @@ ENTRY(__gnu_thumb1_case_shi)
 	lsls	r1, r1, #1
 	add	lr, lr, r1
 	pop	{r0, r1}
-	bx	lr
+	ret	lr
 ENDPROC(__gnu_thumb1_case_shi)
 .popsection
 
@@ -421,7 +421,7 @@ ENTRY(__gnu_thumb1_case_uhi)
 	lsls	r1, r1, #1
 	add	lr, lr, r1
 	pop	{r0, r1}
-	bx	lr
+	ret	lr
 ENDPROC(__gnu_thumb1_case_uhi)
 .popsection
 #endif
diff --git a/arch/arm/lib/memcpy.S b/arch/arm/lib/memcpy.S
index eee7a219ce36..a1c996f94ef2 100644
--- a/arch/arm/lib/memcpy.S
+++ b/arch/arm/lib/memcpy.S
@@ -59,7 +59,7 @@
 #endif
 ENTRY(memcpy)
 		cmp	r0, r1
-		bxeq	lr
+		reteq	lr
 
 		enter	r4, lr
 
@@ -148,7 +148,7 @@ ENTRY(memcpy)
 		str1b	r0, ip, cs, abort=21f
 
 		exit	r4, lr
-		bx	lr
+		ret	lr
 
 9:		rsb	ip, ip, #4
 		cmp	ip, #2
@@ -258,7 +258,7 @@ ENTRY(memcpy)
 
 	.macro	copy_abort_end
 	ldmfd	sp!, {r4, lr}
-	bx	lr
+	ret	lr
 	.endm
 
 ENDPROC(memcpy)
diff --git a/arch/arm/lib/relocate.S b/arch/arm/lib/relocate.S
index 5102bfabde4a..dd6f2e3bd5e0 100644
--- a/arch/arm/lib/relocate.S
+++ b/arch/arm/lib/relocate.S
@@ -61,7 +61,7 @@ ENTRY(relocate_vectors)
 	stmia	r1!, {r2-r8,r10}
 #endif
 #endif
-	bx	lr
+	ret	lr
 
 ENDPROC(relocate_vectors)
 
@@ -127,13 +127,7 @@ relocate_done:
 	mcr	p15, 0, r0, c7, c10, 4	/* drain write buffer */
 #endif
 
-	/* ARMv4- don't know bx lr but the assembler fails to see that */
-
-#ifdef __ARM_ARCH_4__
-	mov	pc, lr
-#else
-	bx	lr
-#endif
+	ret	lr
 
 ENDPROC(relocate_code)
 
diff --git a/arch/arm/lib/setjmp.S b/arch/arm/lib/setjmp.S
index 176a1d5315bf..2f041aeef01c 100644
--- a/arch/arm/lib/setjmp.S
+++ b/arch/arm/lib/setjmp.S
@@ -17,7 +17,7 @@ ENTRY(setjmp)
 	mov  ip, sp
 	stm  a1, {v1-v8, ip, lr}
 	mov  a1, #0
-	bx   lr
+	ret  lr
 ENDPROC(setjmp)
 .popsection
 
@@ -31,6 +31,6 @@ ENTRY(longjmp)
 	bne  1f
 	mov  a1, #1
 1:
-	bx   lr
+	ret  lr
 ENDPROC(longjmp)
 .popsection
-- 
2.34.1

Re: [PATCH v2] arm: ARMv4 assembly compatibility

[Tom Rini]

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On Sun, Aug 21, 2022 at 04:34:20PM +0300, Sergei Antonov wrote:

> There is currently a problem that U-Boot can not work on ARMv4
> because assembly imlementations of memcpy() and some other functions
> use "bx lr" instruction that is not available on ARMv4 ("mov pc, lr"
> should be used instead).
> 
> A working preprocessor-based solution to this problem is found in
> arch/arm/lib/relocate.S. Move it to the "ret" macro in
> arch/arm/include/asm/assembler.h and change all "bx lr" code
> to "ret lr" in functions that may run on ARMv4. Linux source code
> deals with this problem in the same manner.
> 
> v1 -> v2:
> Comment update. Pointed out by Andre Przywara.
> 
> Signed-off-by: Sergei Antonov <saproj@gmail.com>
> CC: Samuel Holland <samuel@sholland.org>
> CC: Ye Li <ye.li@nxp.com>
> CC: Simon Glass <sjg@chromium.org>
> CC: Andre Przywara <andre.przywara@arm.com>
> CC: Marek Vasut <marex@denx.de>
> CC: Sean Anderson <sean.anderson@seco.com>
> CC: Tom Rini <trini@konsulko.com>

Applied to u-boot/next, thanks!

-- 
Tom

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