From: Russell King - ARM Linux <linux@armlinux.org.uk> To: "Jason A. Donenfeld" <Jason@zx2c4.com>, Will Deacon <will.deacon@arm.com> Cc: linux-arm-kernel@lists.infradead.org, lkml@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] arm: ensure symbol is a thumb symbol in new binutils Date: Tue, 21 Nov 2017 17:38:57 +0000 [thread overview] Message-ID: <20171121173857.GJ31757@n2100.armlinux.org.uk> (raw) In-Reply-To: <20171121172751.29545-1-Jason@zx2c4.com> On Tue, Nov 21, 2017 at 06:27:51PM +0100, Jason A. Donenfeld wrote: > On older versions of binutils, \sym points to an aligned address. On > newer versions of binutils, \sym sometimes points to the unaligned thumb > address in mysterious and buggy circumstances. In order to homogenize > this behavior, rather than adding 1, we simply OR in 1, so that already > unaligned instructions don't change. This fix is required for a > pedestrian THUMB2_KERNEL to boot without crashing when built with > non-old binutils. > > While it works, the downside is that we have to add an `orr` instruction > to a fast path. The assembler can't do this at assemble time via "|1" > because "invalid operands (.text and *ABS* sections) for `|'", so we're > forced to do this. A better solution would be to have consistent > binutils behavior, or to have some kind of \sym feature detection that > won't turn into a maze of version comparisons. However, it's at the > moment unclear how to achieve this. > > The rest of this commit message contains all of the relevant > information. > > My tests concerned these versions: > broken: GNU ld (Gentoo 2.29.1 p3) 2.29.1 > working: GNU ld (GNU Binutils for Ubuntu) 2.26.1 > > These produced the following code: > --- broken 2017-11-21 17:44:14.523416082 +0100 > +++ working 2017-11-21 17:44:44.548461234 +0100 > @@ -133,7 +133,7 @@ > 160: f01a 0ff0 tst.w sl, #240 ; 0xf0 > 164: d111 bne.n 18a <__sys_trace> > 166: f5b7 7fc8 cmp.w r7, #400 ; 0x190 > - 16a: f2af 1e6a subw lr, pc, #362 ; 0x16a > + 16a: f2af 1e6b subw lr, pc, #363 ; 0x16b > 16e: bf38 it cc > 170: f858 f027 ldrcc.w pc, [r8, r7, lsl #2] > 174: a902 add r1, sp, #8 > > The differing instruction corresponds with this actual line in > arch/arm/kernel/entry-common.S: > badr lr, ret_fast_syscall @ return address > > Running the broken kernel results in a runtime OOPS with: > PC is at ret_fast_syscall+0x4/0x52 > LR is at ret_fast_syscall+0x2/0x52 > > The disassembly of that function for the crashing kernel is: > .text:00000000 ret_fast_syscall ; CODE XREF: sys_syscall+1C↓j > .text:00000000 CPSID I ; jumptable 00000840 cases 15,18-376 > .text:00000002 > .text:00000002 loc_2 ; DATA XREF: sys_syscall-6BA↓o > .text:00000002 LDR.W R2, [R9,#8] > .text:00000006 CMP.W R2, #0xBF000000 > > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> As it just seems to be a limited range of binutils versions that are affected, I'd rather not impact the kernel fast-paths with extra cycles just because binutils decided to change behaviour. I'd prefer to inform people about the problem and get them to change to a non- buggy binutils. This seems to be the second binutils bug that's biting us within the last month... what's going on with binutils QA? arch/arm/Makefile | 7 +++++-- arch/arm/tools/Makefile | 5 ++++- arch/arm/tools/toolcheck | 24 ++++++++++++++++++++++++ 3 files changed, 33 insertions(+), 3 deletions(-) diff --git a/arch/arm/Makefile b/arch/arm/Makefile index 1cfac5119545..9e70d0435121 100644 --- a/arch/arm/Makefile +++ b/arch/arm/Makefile @@ -319,16 +319,19 @@ all: $(notdir $(KBUILD_IMAGE)) $(KBUILD_DTBS) archheaders: $(Q)$(MAKE) $(build)=arch/arm/tools uapi -archprepare: +archprepare: toolcheck $(Q)$(MAKE) $(build)=arch/arm/tools kapi +toolcheck: + $(Q)$(MAKE) $(build)=arch/arm/tools $@ + # Convert bzImage to zImage bzImage: zImage BOOT_TARGETS = zImage Image xipImage bootpImage uImage INSTALL_TARGETS = zinstall uinstall install -PHONY += bzImage $(BOOT_TARGETS) $(INSTALL_TARGETS) +PHONY += bzImage $(BOOT_TARGETS) $(INSTALL_TARGETS) toolcheck bootpImage uImage: zImage zImage: Image diff --git a/arch/arm/tools/Makefile b/arch/arm/tools/Makefile index ddb89a7db36f..fa77351ccefd 100644 --- a/arch/arm/tools/Makefile +++ b/arch/arm/tools/Makefile @@ -23,12 +23,15 @@ uapi-hdrs-y += $(uapi)/unistd-eabi.h targets += $(addprefix ../../../,$(gen-y) $(kapi-hdrs-y) $(uapi-hdrs-y)) -PHONY += kapi uapi +PHONY += kapi uapi toolcheck kapi: $(kapi-hdrs-y) $(gen-y) uapi: $(uapi-hdrs-y) +toolcheck: + @$(CONFIG_SHELL) '$(srctree)/$(src)/toolcheck' + # Create output directory if not already present _dummy := $(shell [ -d '$(kapi)' ] || mkdir -p '$(kapi)') \ $(shell [ -d '$(uapi)' ] || mkdir -p '$(uapi)') diff --git a/arch/arm/tools/toolcheck b/arch/arm/tools/toolcheck index e69de29bb2d1..97bbeeb691da 100644 --- a/arch/arm/tools/toolcheck +++ b/arch/arm/tools/toolcheck @@ -0,0 +1,24 @@ +#!/bin/sh -ex +if grep -q 'CONFIG_THUMB2_KERNEL=y' .config; then + tmp=$(mktemp -d /tmp/binutils-test.XXXXXXXXXX) + cat <<EOF | $AS $ASFLAGS -o $tmp/test.o + .syntax unified + .thumb + .macro badr, reg, sym + adr \reg, \sym + 1 + .endm + +test: + mov r0, #0 + badr lr, test +EOF + if ! $OBJDUMP -d $tmp/test.o | grep -q '4:\s*f2af 0e07'; then + echo "Error: your assembler version produces buggy kernels" >&2 + $AS --version | head -n1 >&2 + rm $tmp/*.o + rmdir $tmp + exit 1 + fi + rm $tmp/*.o + rmdir $tmp +fi -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up According to speedtest.net: 8.21Mbps down 510kbps up
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From: linux@armlinux.org.uk (Russell King - ARM Linux) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH] arm: ensure symbol is a thumb symbol in new binutils Date: Tue, 21 Nov 2017 17:38:57 +0000 [thread overview] Message-ID: <20171121173857.GJ31757@n2100.armlinux.org.uk> (raw) In-Reply-To: <20171121172751.29545-1-Jason@zx2c4.com> On Tue, Nov 21, 2017 at 06:27:51PM +0100, Jason A. Donenfeld wrote: > On older versions of binutils, \sym points to an aligned address. On > newer versions of binutils, \sym sometimes points to the unaligned thumb > address in mysterious and buggy circumstances. In order to homogenize > this behavior, rather than adding 1, we simply OR in 1, so that already > unaligned instructions don't change. This fix is required for a > pedestrian THUMB2_KERNEL to boot without crashing when built with > non-old binutils. > > While it works, the downside is that we have to add an `orr` instruction > to a fast path. The assembler can't do this at assemble time via "|1" > because "invalid operands (.text and *ABS* sections) for `|'", so we're > forced to do this. A better solution would be to have consistent > binutils behavior, or to have some kind of \sym feature detection that > won't turn into a maze of version comparisons. However, it's at the > moment unclear how to achieve this. > > The rest of this commit message contains all of the relevant > information. > > My tests concerned these versions: > broken: GNU ld (Gentoo 2.29.1 p3) 2.29.1 > working: GNU ld (GNU Binutils for Ubuntu) 2.26.1 > > These produced the following code: > --- broken 2017-11-21 17:44:14.523416082 +0100 > +++ working 2017-11-21 17:44:44.548461234 +0100 > @@ -133,7 +133,7 @@ > 160: f01a 0ff0 tst.w sl, #240 ; 0xf0 > 164: d111 bne.n 18a <__sys_trace> > 166: f5b7 7fc8 cmp.w r7, #400 ; 0x190 > - 16a: f2af 1e6a subw lr, pc, #362 ; 0x16a > + 16a: f2af 1e6b subw lr, pc, #363 ; 0x16b > 16e: bf38 it cc > 170: f858 f027 ldrcc.w pc, [r8, r7, lsl #2] > 174: a902 add r1, sp, #8 > > The differing instruction corresponds with this actual line in > arch/arm/kernel/entry-common.S: > badr lr, ret_fast_syscall @ return address > > Running the broken kernel results in a runtime OOPS with: > PC is at ret_fast_syscall+0x4/0x52 > LR is at ret_fast_syscall+0x2/0x52 > > The disassembly of that function for the crashing kernel is: > .text:00000000 ret_fast_syscall ; CODE XREF: sys_syscall+1C?j > .text:00000000 CPSID I ; jumptable 00000840 cases 15,18-376 > .text:00000002 > .text:00000002 loc_2 ; DATA XREF: sys_syscall-6BA?o > .text:00000002 LDR.W R2, [R9,#8] > .text:00000006 CMP.W R2, #0xBF000000 > > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> As it just seems to be a limited range of binutils versions that are affected, I'd rather not impact the kernel fast-paths with extra cycles just because binutils decided to change behaviour. I'd prefer to inform people about the problem and get them to change to a non- buggy binutils. This seems to be the second binutils bug that's biting us within the last month... what's going on with binutils QA? arch/arm/Makefile | 7 +++++-- arch/arm/tools/Makefile | 5 ++++- arch/arm/tools/toolcheck | 24 ++++++++++++++++++++++++ 3 files changed, 33 insertions(+), 3 deletions(-) diff --git a/arch/arm/Makefile b/arch/arm/Makefile index 1cfac5119545..9e70d0435121 100644 --- a/arch/arm/Makefile +++ b/arch/arm/Makefile @@ -319,16 +319,19 @@ all: $(notdir $(KBUILD_IMAGE)) $(KBUILD_DTBS) archheaders: $(Q)$(MAKE) $(build)=arch/arm/tools uapi -archprepare: +archprepare: toolcheck $(Q)$(MAKE) $(build)=arch/arm/tools kapi +toolcheck: + $(Q)$(MAKE) $(build)=arch/arm/tools $@ + # Convert bzImage to zImage bzImage: zImage BOOT_TARGETS = zImage Image xipImage bootpImage uImage INSTALL_TARGETS = zinstall uinstall install -PHONY += bzImage $(BOOT_TARGETS) $(INSTALL_TARGETS) +PHONY += bzImage $(BOOT_TARGETS) $(INSTALL_TARGETS) toolcheck bootpImage uImage: zImage zImage: Image diff --git a/arch/arm/tools/Makefile b/arch/arm/tools/Makefile index ddb89a7db36f..fa77351ccefd 100644 --- a/arch/arm/tools/Makefile +++ b/arch/arm/tools/Makefile @@ -23,12 +23,15 @@ uapi-hdrs-y += $(uapi)/unistd-eabi.h targets += $(addprefix ../../../,$(gen-y) $(kapi-hdrs-y) $(uapi-hdrs-y)) -PHONY += kapi uapi +PHONY += kapi uapi toolcheck kapi: $(kapi-hdrs-y) $(gen-y) uapi: $(uapi-hdrs-y) +toolcheck: + @$(CONFIG_SHELL) '$(srctree)/$(src)/toolcheck' + # Create output directory if not already present _dummy := $(shell [ -d '$(kapi)' ] || mkdir -p '$(kapi)') \ $(shell [ -d '$(uapi)' ] || mkdir -p '$(uapi)') diff --git a/arch/arm/tools/toolcheck b/arch/arm/tools/toolcheck index e69de29bb2d1..97bbeeb691da 100644 --- a/arch/arm/tools/toolcheck +++ b/arch/arm/tools/toolcheck @@ -0,0 +1,24 @@ +#!/bin/sh -ex +if grep -q 'CONFIG_THUMB2_KERNEL=y' .config; then + tmp=$(mktemp -d /tmp/binutils-test.XXXXXXXXXX) + cat <<EOF | $AS $ASFLAGS -o $tmp/test.o + .syntax unified + .thumb + .macro badr, reg, sym + adr \reg, \sym + 1 + .endm + +test: + mov r0, #0 + badr lr, test +EOF + if ! $OBJDUMP -d $tmp/test.o | grep -q '4:\s*f2af 0e07'; then + echo "Error: your assembler version produces buggy kernels" >&2 + $AS --version | head -n1 >&2 + rm $tmp/*.o + rmdir $tmp + exit 1 + fi + rm $tmp/*.o + rmdir $tmp +fi -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up According to speedtest.net: 8.21Mbps down 510kbps up
next prev parent reply other threads:[~2017-11-21 17:39 UTC|newest] Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-11-21 17:27 [PATCH] arm: ensure symbol is a thumb symbol in new binutils Jason A. Donenfeld 2017-11-21 17:27 ` Jason A. Donenfeld 2017-11-21 17:38 ` Russell King - ARM Linux [this message] 2017-11-21 17:38 ` Russell King - ARM Linux 2017-11-21 17:46 ` Jason A. Donenfeld 2017-11-21 17:46 ` Jason A. Donenfeld 2017-11-21 17:49 ` Russell King - ARM Linux 2017-11-21 17:49 ` Russell King - ARM Linux 2017-11-22 23:34 ` Jason A. Donenfeld 2017-11-22 23:34 ` Jason A. Donenfeld 2017-11-23 10:35 ` Russell King - ARM Linux 2017-11-23 10:35 ` Russell King - ARM Linux 2017-11-23 10:47 ` Fwd: " Jason A. Donenfeld 2017-11-23 10:47 ` Jason A. Donenfeld 2017-11-23 11:48 ` [PATCH] arm: detect buggy binutils when in thumb2 mode Jason A. Donenfeld 2017-11-23 11:48 ` Jason A. Donenfeld 2017-11-23 11:50 ` [PATCH v2] " Jason A. Donenfeld 2017-11-23 11:50 ` Jason A. Donenfeld 2017-11-23 12:01 ` Martin Storsjö 2017-11-23 12:01 ` Martin Storsjö 2017-11-23 14:02 ` Fwd: [PATCH] arm: ensure symbol is a thumb symbol in new binutils Russell King - ARM Linux 2017-11-23 14:02 ` Russell King - ARM Linux 2017-11-23 14:26 ` Ard Biesheuvel 2017-11-23 14:26 ` Ard Biesheuvel 2017-11-23 14:26 ` Ard Biesheuvel [not found] ` <765227b5-981d-0cea-c831-73cfe2f58721@redhat.com> [not found] ` <aaf57bb5-13e6-852c-0f67-f72aedef0e79@gmail.com> [not found] ` <254af731-459b-1f1d-2d93-27c5a91e7bfb@redhat.com> 2018-05-31 21:16 ` [Buildroot] " Romain Naour 2018-06-01 8:28 ` Christophe PRIOUZEAU [not found] ` <2a8151c1-644e-a6b0-9a21-2c570ac7000b@redhat.com> 2018-06-05 8:52 ` Christophe PRIOUZEAU [not found] ` <ec2b0134-6c4a-53ff-4ae2-69c3f0646ded@redhat.com> 2018-06-05 14:11 ` Christophe PRIOUZEAU [not found] ` <1d8f302b-5ece-9921-b930-8c4bca61743e@redhat.com> 2018-06-11 14:47 ` Christophe PRIOUZEAU [not found] ` <1d8f302b-5ece-9921-b930-8c4bca61743e@redhat. com> [not found] ` <CAJA7tRbsNa7oTS-1sLs0WpA74RZr0R-v=sCyQxbDam5Gb7fYHA@mail.gmail.com> [not found] ` <be2db8d4-7c12-2706-5084-322aa659c3bc@redhat.com> 2018-06-18 15:04 ` Christophe PRIOUZEAU 2018-06-18 18:29 ` Romain Naour [not found] ` <062a421f-a669-fc1c-91e0-88cf73794414@redhat.com> 2018-06-19 12:27 ` Christophe PRIOUZEAU 2018-01-16 8:43 ` Chen-Yu Tsai
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