linux-kernel - Problems with arm64 compat vdso

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Message-ID: <20190920142738.qlsjwguc6bpnez63@willie-the-truck>
Date:   Fri, 20 Sep 2019 15:27:39 +0100
From:   Will Deacon <will@...nel.org>
To:     vincenzo.frascino@....com
Cc:     linux-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, linux@...linux.org.uk,
        ard.biesheuvel@...aro.org, catalin.marinas@....com
Subject: Problems with arm64 compat vdso

Hi Vincenzo,

I've been running into a few issues with the COMPAT vDSO. Please could
you have a look?

If I do the following:

$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- defconfig
[...]
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfig
[set CONFIG_CROSS_COMPILE_COMPAT_VDSO="arm-linux-gnueabihf-"]
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-

Then I see the following warning:

arch/arm64/Makefile:62: CROSS_COMPILE_COMPAT not defined or empty, the compat vDSO will not be built

even though the compat vDSO *has* been built:

$ file arch/arm64/kernel/vdso32/vdso.so
arch/arm64/kernel/vdso32/vdso.so: ELF 32-bit LSB pie executable, ARM, EABI5 version 1 (SYSV), dynamically linked, BuildID[sha1]=c67f6c786f2d2d6f86c71f708595594aa25247f6, stripped

However, I also get some warnings because arm64 headers are being included
in the compat vDSO build:

In file included from ./arch/arm64/include/asm/thread_info.h:17:0,
                 from ./include/linux/thread_info.h:38,
                 from ./arch/arm64/include/asm/preempt.h:5,
                 from ./include/linux/preempt.h:78,
                 from ./include/linux/spinlock.h:51,
                 from ./include/linux/seqlock.h:36,
                 from ./include/linux/time.h:6,
                 from /usr/local/google/home/willdeacon/work/linux/lib/vdso/gettimeofday.c:7,
                 from <command-line>:0:
./arch/arm64/include/asm/memory.h: In function ‘__tag_set’:
./arch/arm64/include/asm/memory.h:233:15: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
  u64 __addr = (u64)addr & ~__tag_shifted(0xff);
               ^
In file included from ./arch/arm64/include/asm/pgtable-hwdef.h:8:0,
                 from ./arch/arm64/include/asm/processor.h:34,
                 from ./arch/arm64/include/asm/elf.h:118,
                 from ./include/linux/elf.h:5,
                 from ./include/linux/elfnote.h:62,
                 from arch/arm64/kernel/vdso32/note.c:11:
./arch/arm64/include/asm/memory.h: In function ‘__tag_set’:
./arch/arm64/include/asm/memory.h:233:15: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
  u64 __addr = (u64)addr & ~__tag_shifted(0xff);
               ^
Worse, if your compat binutils isn't up-to-date, you'll actually run into
a build failure:

/tmp/ccFCrjUg.s:80: Error: invalid barrier type -- `dmb ishld'
/tmp/ccFCrjUg.s:124: Error: invalid barrier type -- `dmb ishld'

There also appears to be a problem getting the toolchain prefix from Kconfig.
If, for example, I do:

$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- defconfig
[...]
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfig
[set CONFIG_CROSS_COMPILE_COMPAT_VDSO="vincenzo"]
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
arch/arm64/Makefile:64: *** vincenzogcc not found, check CROSS_COMPILE_COMPAT.  Stop.
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfig
[set CONFIG_CROSS_COMPILE_COMPAT_VDSO="arm-linux-gnueabihf-"]
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
arch/arm64/Makefile:64: *** vincenzogcc not found, check CROSS_COMPILE_COMPAT.  Stop.
$ grep CONFIG_CROSS_COMPILE_COMPAT_VDSO .config
CONFIG_CROSS_COMPILE_COMPAT_VDSO="arm-linux-gnueabihf-"

which is irritating, because it seems to force a 'mrproper' if you don't
get the prefix right first time.

Cheers,

Will