Hi Ben, Dave, Russell,

This is addtion to previously posted patch 'ARM: signal: sigreturn_codes should be endian neutral' http://lists.infradead.org/pipermail/linux-arm-kernel/2013-August/195176.htm...

Ben, who graciously agreed to include my above V3 version of patch into his BE series, reported that above patch breaks build of some old architectures.

I believe I am able to reproduce the issue using rpc_defconfig. Build fails with messages like these (full gcc invocation could be found below in Apendix 1):

arch/arm/kernel/sigreturn_codes.S: Assembler messages: arch/arm/kernel/sigreturn_codes.S:46: Error: selected processor does not support THUMB opcodes arch/arm/kernel/sigreturn_codes.S:47: Error: selected processor does not support Thumb mode `movs r7,#((0x900000+119)-0x900000)' <snip>

When I proposed first version of the patch using asm/opcodes.h macros

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

we discussed that it is better to use separate assembler file with right asm mnemonics and let toolchain to do right thing - byte swapping instructions depending on endianity. It was highlighted the assumption is that we have sufficiently thumb-capable tools. In sigreturn_codes.S I explicitly used asm '.thumb' directive. However I failed to realize that even toolchain is thumb-capable it depends on -march=XXX gcc command line option whether gas takes .thumb opcodes or not. For architectures below v6, non t variants (like -march=armv3 used by rpc_defconfig) it fails to compile .S file with .thumb directive in it. Please see below Apendix 2 for small examples.

To fix the issue I considered several options. I created fix patch with my preferred choice, which follows this cover letter, but I am looking for other folks feedback and opinions and/or maybe suggestions for other better ways to address it.

Switch arch with explicity .arch asm directive ----------------------------------------------

The idea of this approach is to switch arm architecture explicitly with '.arch' asm directive inside of sigreturn_codes.S if arch that set by Makefile is too low

Diff will look like this:

diff --git a/arch/arm/kernel/sigreturn_codes.S b/arch/arm/kernel/sigreturn_codes.S index c888c43..3c5d0f2 100644 --- a/arch/arm/kernel/sigreturn_codes.S +++ b/arch/arm/kernel/sigreturn_codes.S @@ -30,6 +30,17 @@ * snippets. */

+#if __LINUX_ARM_ARCH__ <= 4 + /* + * Note we manually set minimally required arch that supports + * required thumb opcodes for early arch versions. It is OK + * for this file to be used in combination with other + * lower arch variants, since these code snippets are only + * used as input data. + */ + .arch armv4t +#endif + .section .rodata .global sigreturn_codes .type sigreturn_codes, #object

Note with this approach if modern abi is used and explicit '.arch armv4t' is used, gas generate "File Attributes" that contain 'Tag_CPU_name: "4T"' and 'Tag_CPU_arch: v4T' tag records. I would like not to have mismatch with other object file so '.arch armv4t' usage is conditional - only for old arch values. Note for rpc_defconfig test case old '-mabi=apcs-gnu' option is used, and in this case no "File Attributes" is generated. Although mixing .o file with different Tag_CPU_arch tags may not be big issue as long as valuea are compatible. I do see in CONFIG_ARCH_MULTIPLATFORM case .o files with 'Tag_CPU_arch: v6K' are mixed with object files with 'Tag_CPU_arch: v7'.

This is my preferred approach. Complete proposed diff follows this cover letter.

Conditional compilation based on __LINUX_ARM_ARCH__ value ---------------------------------------------------------

Use '#if __LINUX_ARM_ARCH__ >= 6' condition around .thumb asm sequences, if not, fallback to constructing opcode manually as original sigretun_codes did. Code will look something like this:

+#if __LINUX_ARM_ARCH__ >= 5 .thumb movs r7, #(__NR_rt_sigreturn - __NR_SYSCALL_BASE) swi #0 +#else + /* + * gas will not take .thumb opcodes for older arch, + * construct them manually + */ + .long (0xdf00 << 16 | 0x2700 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE)) +#endif

this approach is safe bet but manually generated opcodes seems to be step backward

Use asm/opcodes.h macros ------------------------

With this approach we can abandon use of separate .S file and use macros from <asm/opcodes.h>. Effectively it will back out my v3 version of patch and apply v1 version as I posted here:

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

Any other suggestions? ----------------------

Testing -------

I tested LE and BE pandaboard in Linaro tree and BE patch series. Original LTP ./rt_sigactionNN tests have been run.

Tested build of rpc_defconfig which has CONFIG_CPU_32v3 and exhibited build problem. Beyond that I struggle to find old machine that would fail to build.

Also I looked at

kirkwood_defconfig there was no issue with original patch, it is CONFIG_CPU_32v5 which implies -march=armv5te or -march=armv4t, both OK with .thumb

integrator_defconfig there was no issue with original patch, it is CONFIG_CPU_32v4t which implies -march=armv4t, which is OK with .thumb

ixp4xx_defconfig there was no issue with original patch, it is CONFIG_CPU_32v5 and it is in CONFIG_CPU_BIG_ENDIAN=y (BE32). This is compiled with -march=armv5te. sigreturn_codes look OK. Before original patch thumb instrs were swapped.

Any other suggestions for old boards configs to test?

Apendix 1 full failed compile line ----------------------------------

arm-linux-gnueabihf-gcc -Wp,-MD,arch/arm/kernel/.sigreturn_codes.o.d \ -nostdinc -isystem /run/media/kamensky/wd/linaro/gcc-linaro-arm-linux-gnueabihf-4.7-2013.01-20130125_linux/bin/../lib/gcc/arm-linux-gnueabihf/4.7.3/include \ -I/run/media/kamensky/wd/linaro/linux-linaro-core-tracking/091013/linux-linaro-tracking-be/arch/arm/include -Iarch/arm/include/generated \ -Iinclude -I/run/media/kamensky/wd/linaro/linux-linaro-core-tracking/091013/linux-linaro-tracking-be/arch/arm/include/uapi -Iarch/arm/include/generated/uapi \ -I/run/media/kamensky/wd/linaro/linux-linaro-core-tracking/091013/linux-linaro-tracking-be/include/uapi -Iinclude/generated/uapi -include \ /run/media/kamensky/wd/linaro/linux-linaro-core-tracking/091013/linux-linaro-tracking-be/include/linux/kconfig.h -D__KERNEL__ -mlittle-endian \ -Iarch/arm/mach-rpc/include -D__ASSEMBLY__ -mabi=apcs-gnu -mno-thumb-interwork -marm -D__LINUX_ARM_ARCH__=3 -march=armv3 -mtune=strongarm110 \ -include asm/unified.h -msoft-float -gdwarf-2 -c -o arch/arm/kernel/sigreturn_codes.o arch/arm/kernel/sigreturn_codes.S arch/arm/kernel/sigreturn_codes.S: Assembler messages: arch/arm/kernel/sigreturn_codes.S:46: Error: selected processor does not support THUMB opcodes arch/arm/kernel/sigreturn_codes.S:47: Error: selected processor does not support Thumb mode `movs r7,#((0x900000+119)-0x900000)' <snip>

Apendix 2 -march and .thumb simple test case --------------------------------------------

[kamensky@kamensky-w530 linux-linaro-tracking-be]$ cat t.S sigreturn_codes: .thumb movs r7, #157

[kamensky@kamensky-w530 linux-linaro-tracking-be]$ arm-linux-gnueabihf-gcc -nostdinc -mlittle-endian -mno-thumb-interwork -mabi=apcs-gnu -marm -march=armv3 -msoft-float -c -o t.o t.S t.S: Assembler messages: t.S:2: Error: selected processor does not support THUMB opcodes t.S:3: Error: selected processor does not support Thumb mode `movs r7,#157' [kamensky@kamensky-w530 linux-linaro-tracking-be]$ arm-linux-gnueabihf-gcc -nostdinc -mlittle-endian -mno-thumb-interwork -mabi=apcs-gnu -marm -march=armv5 -msoft-float -c -o t.o t.S t.S: Assembler messages: t.S:2: Error: selected processor does not support THUMB opcodes t.S:3: Error: selected processor does not support Thumb mode `movs r7,#157' [kamensky@kamensky-w530 linux-linaro-tracking-be]$ arm-linux-gnueabihf-gcc -nostdinc -mlittle-endian -mno-thumb-interwork -mabi=apcs-gnu -marm -march=armv6 -msoft-float -c -o t.o t.S [kamensky@kamensky-w530 linux-linaro-tracking-be]$ arm-linux-gnueabihf-gcc -nostdinc -mlittle-endian -mno-thumb-interwork -mabi=apcs-gnu -march=armv7 -msoft-float -c -o t.o t.S

Thanks, Victor

Victor Kamensky (1): ARM: signal: sigreturn_codes fix build breakage for old arch

arch/arm/kernel/sigreturn_codes.S | 11 +++++++++++ 1 file changed, 11 insertions(+)