diff mbox series

[RFC] kbuild: add CLANG_TRIPLE to prevent clang from compiling with wrong --target

Message ID 1631173363-40160-1-git-send-email-ashimida@linux.alibaba.com (mailing list archive)
State New, archived
Headers show
Series [RFC] kbuild: add CLANG_TRIPLE to prevent clang from compiling with wrong --target | expand

Commit Message

Dan Li Sept. 9, 2021, 7:42 a.m. UTC 
Kernel compiled with tool chain CROSS_COMPILE=aarch64-linux-android-
will panic during the startup phase.

Clang's --target option comes from $(CROSS_COMPILE). At the time
-fstack-protector-strong is enabled, and compiled with command:
make CC=clang HOSTCC=clang ARCH=arm64 CROSS_COMPILE=aarch64-linux-android-

clang will insert code like:
   mrs     x8, TPIDR_EL0	//default value is zero
   str     x8, [sp]
   ldr     x8, [x8, #40]	//access addr 0x40

instead of the code that accesses __stack_chk_guard to get the
canary, which will cause the kernel to crash due to 0x40
address access.

This patch (from android) is used to remind the user that current
tool chain cannot be used as the "--target" of clang, the user
should specify an additional "--target" through CLANG_TRIPLE.

Signed-off-by: ashimida <ashimida@linux.alibaba.com>
---
 Makefile                 | 6 +++++-
 scripts/clang-android.sh | 4 ++++
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100755 scripts/clang-android.sh

Comments

Nick Desaulniers Sept. 9, 2021, 5:19 p.m. UTC | #1 
On Thu, Sep 9, 2021 at 12:42 AM ashimida <ashimida@linux.alibaba.com> wrote:
>
> Kernel compiled with tool chain CROSS_COMPILE=aarch64-linux-android-
> will panic during the startup phase.
>
> Clang's --target option comes from $(CROSS_COMPILE). At the time
> -fstack-protector-strong is enabled, and compiled with command:
> make CC=clang HOSTCC=clang ARCH=arm64 CROSS_COMPILE=aarch64-linux-android-
>
> clang will insert code like:
>    mrs     x8, TPIDR_EL0        //default value is zero
>    str     x8, [sp]
>    ldr     x8, [x8, #40]        //access addr 0x40
>
> instead of the code that accesses __stack_chk_guard to get the
> canary, which will cause the kernel to crash due to 0x40
> address access.
>
> This patch (from android) is used to remind the user that current
> tool chain cannot be used as the "--target" of clang, the user
> should specify an additional "--target" through CLANG_TRIPLE.

Hi Ashimida,
Thanks for sending this patch; I recognize it from Android, which we
had to carry for years due to:
1. reliance on GNU `as` ie. "GAS"
2. not distributing binary prefixes of GNU binutils with a target
triple that clang recognized. (ie. Android's binutils were prefixed
aarch64-linux-android- while Clang expected something more like
aarch64-linux-gnu for --target=)

We solved this by working out the issues in clang's assembler.  With
LLVM=1 LLVM_IAS=1, we no longer rely on GNU binutils, and no longer
need such patch.  You'll find it's been dropped from Android Common
Kernels now.  With mainline, LLVM_IAS=1 is now the default when
building with LLVM=1, and CROSS_COMPILE is now inferred from ARCH for
LLVM=1 as well.

So all you should need is:
$ ARCH=arm64 make LLVM=1 -j$(nproc)

Is there a reason why the above doesn't work for you?  I do not wish
to see this patch upstream (or downstream; it should be unnecessary).

>
> Signed-off-by: ashimida <ashimida@linux.alibaba.com>
> ---
>  Makefile                 | 6 +++++-
>  scripts/clang-android.sh | 4 ++++
>  2 files changed, 9 insertions(+), 1 deletion(-)
>  create mode 100755 scripts/clang-android.sh
>
> diff --git a/Makefile b/Makefile
> index 61741e9..09bb314 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -586,7 +586,11 @@ CC_VERSION_TEXT = $(subst $(pound),,$(shell $(CC) --version 2>/dev/null | head -
>
>  ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
>  ifneq ($(CROSS_COMPILE),)
> -CLANG_FLAGS    += --target=$(notdir $(CROSS_COMPILE:%-=%))
> +CLANG_TRIPLE    ?= $(CROSS_COMPILE)
> +CLANG_FLAGS     += --target=$(notdir $(CLANG_TRIPLE:%-=%))
> +ifeq ($(shell $(srctree)/scripts/clang-android.sh $(CC) $(CLANG_FLAGS)), y)
> +$(error "Clang with Android --target detected. Did you specify CLANG_TRIPLE?")
> +endif
>  endif
>  ifeq ($(LLVM_IAS),1)
>  CLANG_FLAGS    += -integrated-as
> diff --git a/scripts/clang-android.sh b/scripts/clang-android.sh
> new file mode 100755
> index 0000000..9186c4f
> --- /dev/null
> +++ b/scripts/clang-android.sh
> @@ -0,0 +1,4 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +
> +$* -dM -E - </dev/null 2>&1 | grep -q __ANDROID__ && echo "y"
> --
> 2.7.4
>
Dan Li Sept. 11, 2021, 11:55 a.m. UTC | #2 
Hi Desaulniers,

I now understand the meaning here, the command works fine for me.

Thank you very much for the reply!

On 9/10/21 1:19 AM, Nick Desaulniers wrote:
 > On Thu, Sep 9, 2021 at 12:42 AM ashimida <ashimida@linux.alibaba.com> 
wrote:
 >>
 >> Kernel compiled with tool chain CROSS_COMPILE=aarch64-linux-android-
 >> will panic during the startup phase.
 >>
 >> Clang's --target option comes from $(CROSS_COMPILE). At the time
 >> -fstack-protector-strong is enabled, and compiled with command:
 >> make CC=clang HOSTCC=clang ARCH=arm64 
CROSS_COMPILE=aarch64-linux-android-
 >>
 >> clang will insert code like:
 >>     mrs     x8, TPIDR_EL0        //default value is zero
 >>     str     x8, [sp]
 >>     ldr     x8, [x8, #40]        //access addr 0x40
 >>
 >> instead of the code that accesses __stack_chk_guard to get the
 >> canary, which will cause the kernel to crash due to 0x40
 >> address access.
 >>
 >> This patch (from android) is used to remind the user that current
 >> tool chain cannot be used as the "--target" of clang, the user
 >> should specify an additional "--target" through CLANG_TRIPLE.
 >
 > Hi Ashimida,
 > Thanks for sending this patch; I recognize it from Android, which we
 > had to carry for years due to:
 > 1. reliance on GNU `as` ie. "GAS"
 > 2. not distributing binary prefixes of GNU binutils with a target
 > triple that clang recognized. (ie. Android's binutils were prefixed
 > aarch64-linux-android- while Clang expected something more like
 > aarch64-linux-gnu for --target=)
 >
 > We solved this by working out the issues in clang's assembler.  With
 > LLVM=1 LLVM_IAS=1, we no longer rely on GNU binutils, and no longer
 > need such patch.  You'll find it's been dropped from Android Common
 > Kernels now.  With mainline, LLVM_IAS=1 is now the default when
 > building with LLVM=1, and CROSS_COMPILE is now inferred from ARCH for
 > LLVM=1 as well.
 >
 > So all you should need is:
 > $ ARCH=arm64 make LLVM=1 -j$(nproc)
 >
 > Is there a reason why the above doesn't work for you?  I do not wish
 > to see this patch upstream (or downstream; it should be unnecessary).
 >
 >>
 >> Signed-off-by: ashimida <ashimida@linux.alibaba.com>
 >> ---
 >>   Makefile                 | 6 +++++-
 >>   scripts/clang-android.sh | 4 ++++
 >>   2 files changed, 9 insertions(+), 1 deletion(-)
 >>   create mode 100755 scripts/clang-android.sh
 >>
 >> diff --git a/Makefile b/Makefile
 >> index 61741e9..09bb314 100644
 >> --- a/Makefile
 >> +++ b/Makefile
 >> @@ -586,7 +586,11 @@ CC_VERSION_TEXT = $(subst $(pound),,$(shell 
$(CC) --version 2>/dev/null | head -
 >>
 >>   ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
 >>   ifneq ($(CROSS_COMPILE),)
 >> -CLANG_FLAGS    += --target=$(notdir $(CROSS_COMPILE:%-=%))
 >> +CLANG_TRIPLE    ?= $(CROSS_COMPILE)
 >> +CLANG_FLAGS     += --target=$(notdir $(CLANG_TRIPLE:%-=%))
 >> +ifeq ($(shell $(srctree)/scripts/clang-android.sh $(CC) 
$(CLANG_FLAGS)), y)
 >> +$(error "Clang with Android --target detected. Did you specify 
CLANG_TRIPLE?")
 >> +endif
 >>   endif
 >>   ifeq ($(LLVM_IAS),1)
 >>   CLANG_FLAGS    += -integrated-as
 >> diff --git a/scripts/clang-android.sh b/scripts/clang-android.sh
 >> new file mode 100755
 >> index 0000000..9186c4f
 >> --- /dev/null
 >> +++ b/scripts/clang-android.sh
 >> @@ -0,0 +1,4 @@
 >> +#!/bin/sh
 >> +# SPDX-License-Identifier: GPL-2.0
 >> +
 >> +$* -dM -E - </dev/null 2>&1 | grep -q __ANDROID__ && echo "y"
 >> --
 >> 2.7.4
 >>
 >
 >
diff mbox series

Patch

diff --git a/Makefile b/Makefile
index 61741e9..09bb314 100644
--- a/Makefile
+++ b/Makefile
@@ -586,7 +586,11 @@  CC_VERSION_TEXT = $(subst $(pound),,$(shell $(CC) --version 2>/dev/null | head -
 
 ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
 ifneq ($(CROSS_COMPILE),)
-CLANG_FLAGS	+= --target=$(notdir $(CROSS_COMPILE:%-=%))
+CLANG_TRIPLE    ?= $(CROSS_COMPILE)
+CLANG_FLAGS     += --target=$(notdir $(CLANG_TRIPLE:%-=%))
+ifeq ($(shell $(srctree)/scripts/clang-android.sh $(CC) $(CLANG_FLAGS)), y)
+$(error "Clang with Android --target detected. Did you specify CLANG_TRIPLE?")
+endif
 endif
 ifeq ($(LLVM_IAS),1)
 CLANG_FLAGS	+= -integrated-as
diff --git a/scripts/clang-android.sh b/scripts/clang-android.sh
new file mode 100755
index 0000000..9186c4f
--- /dev/null
+++ b/scripts/clang-android.sh
@@ -0,0 +1,4 @@ 
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+$* -dM -E - </dev/null 2>&1 | grep -q __ANDROID__ && echo "y"