[PATCH v3 0/1] ARM: signal: sigreturn_codes should be endian neutral to work in BE8

[PATCH v3 0/1] ARM: signal: sigreturn_codes should be endian neutral to work in BE8

[Victor Kamensky]

This is third version of patch that fixes rt_sig* ltp failures
in case of big endian V7 kernel. It make sigreturn_codes snippets
endian neutral. In this version of the patch problem is fixed by
using separate .S file with snippets written with regular asm
mnemonic. With such change compiler/linker take care of all needed
byteswaps in case of BE8 mode.

This approach was suggested on the following thread:

  http://lists.infradead.org/pipermail/linux-arm-kernel/2013-August/191543.html

Changes were tested on V7 in both BE and LE modes

Changes from v2:
  Incorporated Dave's comments that he gave on
    http://lists.infradead.org/pipermail/linux-arm-kernel/2013-August/191879.html

  Added comment that explains why sigreturn_codes size is 7 words

  Note I could not implemented defensive snippet, that Dave suggested, in
  asm that asserts sigreturn_codes size in asm wrt one that declared in 
  C file. The issue is in gas handling movs instruction, please see above 
  thread for details. So we should rely on comment in the code to make
  sure that code maintained correctly further. Note it was not functional 
  piece anyway. I think it is OK to omit it.

Changes from v1:
  Use separate .S file rather than <asm/opcodes.h> instruction
  byteswaping macros

Victor Kamensky (1):
  ARM: signal: sigreturn_codes should be endian neutral to work in BE8

 arch/arm/kernel/Makefile          |  3 +-
 arch/arm/kernel/signal.c          | 24 +-------------
 arch/arm/kernel/sigreturn_codes.S | 69 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+), 24 deletions(-)
 create mode 100644 arch/arm/kernel/sigreturn_codes.S

-- 
1.8.1.4

[PATCH v3 1/1] ARM: signal: sigreturn_codes should be endian neutral to work in BE8

[Victor Kamensky]

In case of BE8 kernel data is in BE order whereas code stays in LE
order. Move sigreturn_codes to separate .S file and use proper
assembler mnemonics for these code snippets. In this case compiler
will take care of proper instructions byteswaps for BE8 case.
Change assumes that sufficiently Thumb-capable tools are used to
build kernel.

Problem was discovered during ltp testing of BE system: all rt_sig*
tests failed. Tested against the same tests in both BE and LE modes.

Signed-off-by: Victor Kamensky <victor.kamensky@linaro.org>
---
 arch/arm/kernel/Makefile          |  3 +-
 arch/arm/kernel/signal.c          | 24 +-------------
 arch/arm/kernel/sigreturn_codes.S | 69 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+), 24 deletions(-)
 create mode 100644 arch/arm/kernel/sigreturn_codes.S

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 86d10dd..0722155 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -17,7 +17,8 @@ CFLAGS_REMOVE_return_address.o = -pg
 
 obj-y		:= elf.o entry-common.o irq.o opcodes.o \
 		   process.o ptrace.o return_address.o \
-		   setup.o signal.o stacktrace.o sys_arm.o time.o traps.o
+		   setup.o signal.o sigreturn_codes.o \
+		   stacktrace.o sys_arm.o time.o traps.o
 
 obj-$(CONFIG_ATAGS)		+= atags_parse.o
 obj-$(CONFIG_ATAGS_PROC)	+= atags_proc.o
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index ab33042..64845fc 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -21,29 +21,7 @@
 #include <asm/unistd.h>
 #include <asm/vfp.h>
 
-/*
- * For ARM syscalls, we encode the syscall number into the instruction.
- */
-#define SWI_SYS_SIGRETURN	(0xef000000|(__NR_sigreturn)|(__NR_OABI_SYSCALL_BASE))
-#define SWI_SYS_RT_SIGRETURN	(0xef000000|(__NR_rt_sigreturn)|(__NR_OABI_SYSCALL_BASE))
-
-/*
- * With EABI, the syscall number has to be loaded into r7.
- */
-#define MOV_R7_NR_SIGRETURN	(0xe3a07000 | (__NR_sigreturn - __NR_SYSCALL_BASE))
-#define MOV_R7_NR_RT_SIGRETURN	(0xe3a07000 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))
-
-/*
- * For Thumb syscalls, we pass the syscall number via r7.  We therefore
- * need two 16-bit instructions.
- */
-#define SWI_THUMB_SIGRETURN	(0xdf00 << 16 | 0x2700 | (__NR_sigreturn - __NR_SYSCALL_BASE))
-#define SWI_THUMB_RT_SIGRETURN	(0xdf00 << 16 | 0x2700 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))
-
-static const unsigned long sigreturn_codes[7] = {
-	MOV_R7_NR_SIGRETURN,    SWI_SYS_SIGRETURN,    SWI_THUMB_SIGRETURN,
-	MOV_R7_NR_RT_SIGRETURN, SWI_SYS_RT_SIGRETURN, SWI_THUMB_RT_SIGRETURN,
-};
+extern const unsigned long sigreturn_codes[7];
 
 static unsigned long signal_return_offset;
 
diff --git a/arch/arm/kernel/sigreturn_codes.S b/arch/arm/kernel/sigreturn_codes.S
new file mode 100644
index 0000000..c888c43
--- /dev/null
+++ b/arch/arm/kernel/sigreturn_codes.S
@@ -0,0 +1,69 @@
+/*
+ * sigreturn_codes.S - code sinpets for sigreturn syscalls
+ *
+ * Created by:	Victor Kamensky, 2013-08-13
+ * Copyright:	(C) 2013  Linaro Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <asm/unistd.h>
+
+/*
+ * For ARM syscalls, we encode the syscall number into the instruction.
+ * With EABI, the syscall number has to be loaded into r7. As result
+ * ARM syscall sequence snippet will have move and svc in .arm encoding
+ *
+ * For Thumb syscalls, we pass the syscall number via r7.  We therefore
+ * need two 16-bit instructions in .thumb encoding
+ *
+ * Please note sigreturn_codes code are not executed in place. Instead
+ * they just copied by kernel into appropriate places. Code inside of
+ * arch/arm/kernel/signal.c is very sensitive to layout of these code
+ * snippets.
+ */
+
+	.section .rodata
+	.global sigreturn_codes
+	.type	sigreturn_codes, #object
+
+	.arm
+
+sigreturn_codes:
+
+	/* ARM sigreturn syscall code snippet */
+	mov	r7, #(__NR_sigreturn - __NR_SYSCALL_BASE)
+	swi	#(__NR_sigreturn)|(__NR_OABI_SYSCALL_BASE)
+
+	/* Thumb sigreturn syscall code snippet */
+	.thumb
+	movs	r7, #(__NR_sigreturn - __NR_SYSCALL_BASE)
+	swi	#0
+
+	/* ARM sigreturn_rt syscall code snippet */
+	.arm
+	mov	r7, #(__NR_rt_sigreturn - __NR_SYSCALL_BASE)
+	swi	#(__NR_rt_sigreturn)|(__NR_OABI_SYSCALL_BASE)
+
+	/* Thumb sigreturn_rt syscall code snippet */
+	.thumb
+	movs	r7, #(__NR_rt_sigreturn - __NR_SYSCALL_BASE)
+	swi	#0
+
+	/*
+	 * Note on addtional space: setup_return in signal.c
+	 * algorithm uses two words copy regardless whether
+	 * it is thumb case or not, so we need additional
+	 * word after real last entry.
+	 */
+	.arm
+	.space	4
+
+	.size	sigreturn_codes, . - sigreturn_codes
-- 
1.8.1.4

[PATCH v3 1/1] ARM: signal: sigreturn_codes should be endian neutral to work in BE8

[Dave Martin]

On Tue, Aug 27, 2013 at 10:41:57PM -0700, Victor Kamensky wrote:
> In case of BE8 kernel data is in BE order whereas code stays in LE
> order. Move sigreturn_codes to separate .S file and use proper
> assembler mnemonics for these code snippets. In this case compiler
> will take care of proper instructions byteswaps for BE8 case.
> Change assumes that sufficiently Thumb-capable tools are used to
> build kernel.
> 
> Problem was discovered during ltp testing of BE system: all rt_sig*
> tests failed. Tested against the same tests in both BE and LE modes.

This looks OK to me.

Reviewed-by: Dave Martin <Dave.Martin@arm.com>

> 
> Signed-off-by: Victor Kamensky <victor.kamensky@linaro.org>
> ---
>  arch/arm/kernel/Makefile          |  3 +-
>  arch/arm/kernel/signal.c          | 24 +-------------
>  arch/arm/kernel/sigreturn_codes.S | 69 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 72 insertions(+), 24 deletions(-)
>  create mode 100644 arch/arm/kernel/sigreturn_codes.S
> 
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index 86d10dd..0722155 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -17,7 +17,8 @@ CFLAGS_REMOVE_return_address.o = -pg
>  
>  obj-y		:= elf.o entry-common.o irq.o opcodes.o \
>  		   process.o ptrace.o return_address.o \
> -		   setup.o signal.o stacktrace.o sys_arm.o time.o traps.o
> +		   setup.o signal.o sigreturn_codes.o \
> +		   stacktrace.o sys_arm.o time.o traps.o
>  
>  obj-$(CONFIG_ATAGS)		+= atags_parse.o
>  obj-$(CONFIG_ATAGS_PROC)	+= atags_proc.o
> diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
> index ab33042..64845fc 100644
> --- a/arch/arm/kernel/signal.c
> +++ b/arch/arm/kernel/signal.c
> @@ -21,29 +21,7 @@
>  #include <asm/unistd.h>
>  #include <asm/vfp.h>
>  
> -/*
> - * For ARM syscalls, we encode the syscall number into the instruction.
> - */
> -#define SWI_SYS_SIGRETURN	(0xef000000|(__NR_sigreturn)|(__NR_OABI_SYSCALL_BASE))
> -#define SWI_SYS_RT_SIGRETURN	(0xef000000|(__NR_rt_sigreturn)|(__NR_OABI_SYSCALL_BASE))
> -
> -/*
> - * With EABI, the syscall number has to be loaded into r7.
> - */
> -#define MOV_R7_NR_SIGRETURN	(0xe3a07000 | (__NR_sigreturn - __NR_SYSCALL_BASE))
> -#define MOV_R7_NR_RT_SIGRETURN	(0xe3a07000 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))
> -
> -/*
> - * For Thumb syscalls, we pass the syscall number via r7.  We therefore
> - * need two 16-bit instructions.
> - */
> -#define SWI_THUMB_SIGRETURN	(0xdf00 << 16 | 0x2700 | (__NR_sigreturn - __NR_SYSCALL_BASE))
> -#define SWI_THUMB_RT_SIGRETURN	(0xdf00 << 16 | 0x2700 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))
> -
> -static const unsigned long sigreturn_codes[7] = {
> -	MOV_R7_NR_SIGRETURN,    SWI_SYS_SIGRETURN,    SWI_THUMB_SIGRETURN,
> -	MOV_R7_NR_RT_SIGRETURN, SWI_SYS_RT_SIGRETURN, SWI_THUMB_RT_SIGRETURN,
> -};
> +extern const unsigned long sigreturn_codes[7];
>  
>  static unsigned long signal_return_offset;
>  
> diff --git a/arch/arm/kernel/sigreturn_codes.S b/arch/arm/kernel/sigreturn_codes.S
> new file mode 100644
> index 0000000..c888c43
> --- /dev/null
> +++ b/arch/arm/kernel/sigreturn_codes.S
> @@ -0,0 +1,69 @@
> +/*
> + * sigreturn_codes.S - code sinpets for sigreturn syscalls
> + *
> + * Created by:	Victor Kamensky, 2013-08-13
> + * Copyright:	(C) 2013  Linaro Limited
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <asm/unistd.h>
> +
> +/*
> + * For ARM syscalls, we encode the syscall number into the instruction.
> + * With EABI, the syscall number has to be loaded into r7. As result
> + * ARM syscall sequence snippet will have move and svc in .arm encoding
> + *
> + * For Thumb syscalls, we pass the syscall number via r7.  We therefore
> + * need two 16-bit instructions in .thumb encoding
> + *
> + * Please note sigreturn_codes code are not executed in place. Instead
> + * they just copied by kernel into appropriate places. Code inside of
> + * arch/arm/kernel/signal.c is very sensitive to layout of these code
> + * snippets.
> + */
> +
> +	.section .rodata
> +	.global sigreturn_codes
> +	.type	sigreturn_codes, #object
> +
> +	.arm
> +
> +sigreturn_codes:
> +
> +	/* ARM sigreturn syscall code snippet */
> +	mov	r7, #(__NR_sigreturn - __NR_SYSCALL_BASE)
> +	swi	#(__NR_sigreturn)|(__NR_OABI_SYSCALL_BASE)
> +
> +	/* Thumb sigreturn syscall code snippet */
> +	.thumb
> +	movs	r7, #(__NR_sigreturn - __NR_SYSCALL_BASE)
> +	swi	#0
> +
> +	/* ARM sigreturn_rt syscall code snippet */
> +	.arm
> +	mov	r7, #(__NR_rt_sigreturn - __NR_SYSCALL_BASE)
> +	swi	#(__NR_rt_sigreturn)|(__NR_OABI_SYSCALL_BASE)
> +
> +	/* Thumb sigreturn_rt syscall code snippet */
> +	.thumb
> +	movs	r7, #(__NR_rt_sigreturn - __NR_SYSCALL_BASE)
> +	swi	#0
> +
> +	/*
> +	 * Note on addtional space: setup_return in signal.c
> +	 * algorithm uses two words copy regardless whether
> +	 * it is thumb case or not, so we need additional
> +	 * word after real last entry.
> +	 */
> +	.arm
> +	.space	4
> +
> +	.size	sigreturn_codes, . - sigreturn_codes
> -- 
> 1.8.1.4
> 
> 
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