Bugs

This project involves different code bases with many inter-dependencies. As a result issues can be in different categories: LLVM, Clang, Linux Kernel, etc.

I you want to work on something from the list below, please assign it to yourself. Probably best first to discuss it on the mailing list or IRC Channel (#llvmlinux on OFTC).

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Clang/LLVM Issues

Architecture Independent Clang/LLVM Issues

0LLVM Issues: 2 (50%)4


LLVM Issues
Name Status Assigned BugID Description
QEMU build issue In Progress Tinti QEMU does not build with "android" toolchain but builds with "codesourcery". In theory these toolchains would not be used in QEMU build process. (needs to be re-checked)
LLVM meta In Progress 4068 Meta bug report about building the Linux Kernel with LLVM

(tracking meta-bug for LLVM/clang to work with the Linux kernel)

LLVM VLAIS Completed 9254 IPtables doesn't build with clang (VLAIS Issue)

(There is a patch for this in the Linux kernel patches which is being sent upstream)

SROA bug Completed Tinti 14034 Clang uses 100% of CPU and all system memory or crashes if new SROA code is enabled.

Workaround: use "-mllvm -use-new-sroa=false"

Fixed in http://llvm.org/bugs/show_bug.cgi?id=14034

LLVM IA Unassigned Integrated Assmebler cannoy be used to build the kernel

Clang/LLVM Issues Specific to ARM

</todo>

0LLVM ARM Issues: 3 (75%)4
LLVM ARM Issues
Name Status Assigned BugID Description
arm gcc asm Completed LLVM does not support the GCC inline assembly extensions used in atomic.h for 64bit instructions (%H0, etc)
64-bit types Completed QuIC 11753 Incorrect code generated for 64bit types on ARM

(Submitted fix to upstream, working on acceptance. LLVMLinux still using hack for now)

Clang Build with Linaro Completed Mark C Linaro 12698 When vexpress make kernel-build is used with CROSS_ARM_TOOLCHAIN=linaro the following error occurs:

It seems that the 4.6 version of the Linaro assembler handles -march=all differently than the Android 4.6 assembler. It seems to be an issue with the version of binutils used in the Linaro toolchain (2.22 vs 2.21).

The version of the Linaro assembler that I tried (2012.07-20120720) cannot successfully build the versatile express kernel.

/llvmlinux/toolchain/clang/install/bin/clang \
-ccc-host-triple arm-none-gnueabi -ccc-gcc-name arm-linux-gnueabihf-gcc -march=armv7-a \
-mfloat-abi=softfp -mfpu=neon -fno-builtin -Wp,-MD,arch/arm/boot/compressed/.head.o.d \
-nostdinc -isystem /llvmlinux/toolchain/clang/install/bin/../lib/clang/3.2/include \
-I/llvmlinux/targets/vexpress/src/linux/arch/arm/include -Iarch/arm/include/generated \
-Iinclude -include /llvmlinux/targets/vexpress/src/linux/include/linux/kconfig.h \
-D__KERNEL__ -Iarch/arm/mach-vexpress/include -Iarch/arm/plat-versatile/include \
-D__ASSEMBLY__ -D__LINUX_ARM_ARCH__=7 -march=armv7-a -include asm/unified.h \
-msoft-float -gdwarf-2 -Wa,-march=all -DTEXT_OFFSET=0x00008000 -c -o \
arch/arm/boot/compressed/head.o arch/arm/boot/compressed/head.S
arm-linux-gnueabihf-gcc: error: unrecognized argument in option '-march=all'
arm-linux-gnueabihf-gcc: note: valid arguments to '-march=' are: armv2 armv2a armv3 armv3m \
armv4 armv4t armv5 armv5e armv5t armv5te armv6 armv6-m armv6j armv6k armv6s-m armv6t2 armv6z \
armv6zk armv7 armv7-a armv7-m armv7-r armv7e-m ep9312 iwmmxt iwmmxt2 native
clang-3: error: assembler (via gcc) command failed with exit code 1 (use -v to see invocation)
make[3]: *** [arch/arm/boot/compressed/head.o] Error 1
make[2]: *** [arch/arm/boot/compressed/vmlinux] Error 2
make[1]: *** [zImage] Error 2
make[1]: Leaving directory `/llvmlinux/targets/vexpress/src/linux'

The flag is set in arch/arm/boot/compressed/Makefile:

asflags-y := -Wa,-march=all

The error does not occur when using the Android 4.6 assembler with clang.

Linaro:

$ arm-linux-gnueabihf-as -v
GNU assembler version 2.22 (arm-linux-gnueabihf) using BFD version \
(crosstool-NG linaro-1.13.1-2012.07-20120720 - Linaro GCC 2012.07) 2.22

Android:

$ arm-linux-androideabi-as -v
GNU assembler version 2.21 (arm-linux-androideabi) using BFD version (GNU Binutils) 2.21

Interestingly, the linaro compiler can compile the kernel (without clang) as it seems to work around the problem in the gcc front end.

Linaro toolchain lead said this will be fixed in binutils 2.23. Waiting for a newrer version of the compiler based on binutils 2.23.

aapcs Unassigned 11326 -mabi=aapcs-linux generates incorrect code

(Current workaround is to remove this flag, but enum lengths may not be 4 bytes)

(low priority, needs to be rec-confirmed)

Clang/LLVM Issues Specific to x86/x86_64

0LLVM x86 Issues: 4 (50%)8
LLVM x86 Issues
Name Status Assigned BugID Description
register variables Completed 2522 Global register variables not supported. Workarounds for the kernel possible (rewrite w/o global register variable).

(high priority)

.macro args On Hold jsm 9248 No support for .macro with arguments - WIP upstream - rechecking

(high priority)

segment override In Progress wash 9385 MC assembler doesn't accept segment override for movs/lods

(high priority)

udivdi3 Completed jsm 9387 LLVM generates call to __udivdi3 by constant instead of inlining multiply sequence

--> Work around in the Linux Kernel patches (do_div())

Note: LLVM Bug 9387 now marked closed.

Implicit conversion In Progress wash 9425 Implicit conversion warning for impossible path

(medium priority)

missing cc args Unassigned 9457 Clang's missing -ffixed-REG, -fcall-used-REG, -fcall-saved-REG (optimization - HARD!)

(low priority)

codegen Completed 9506 CodeGen assert on invalid inline assembly

(low priority)

extra brackets Completed 9379 MC assembler doesn't recognize inl (%%dx)

(upstream won't fix)

Clang/LLVM Issues Specific to MIPS

0LLVM Mips Issues: 1 (50%)2
LLVM Mips Issues
Name Status Assigned BugID Description
register variables Completed Global register variables not supported.
IAS Unassigned Integrated Assembler does not accept all assembly used in Linux

Checker: Static Analyzer

0Clang Checker: 1 (100%)1
Clang Checker
Name Status Assigned BugID Description
output crash Completed wash Checker crashes when output directory is specified

(high priority)

Linux Kernel Issues

Architecture Independent Linux Kernel Issues

There are instances where the Linux Kernel uses non C99 compliant features of GCC that the LLVM maintainers currently do not plan to support.

0Kernel Issues: 10 (83.33%)12
Kernel Issues
Name Status Assigned BugID Description
operand widths On Hold Warning while compiling the kernel:

"the size being stored is truncated, use a modifier to specify the size [-Wasm-operand-widths]"

Currently disabled with "-Wno-asm-operand-widths"

Expicit Registers Completed Mark C Explicit register variables (non C99 compliant GCC feature)
VLAIS Completed Mark C behanw Variable length arrays in structs (non C99 compliant GGC feature)

Work around for LLVM Bug 9254

All patches sent upstream to the various subsystem maintainers.

Nested Funtions Completed Mark C Local/nested functions (non C99 compliant GCC feature)
segments Completed Mark C, JSM Differences in the way the segments are resolved requiring more data and functions to be marked with __refdata. __initdata, or __exitdata.

(Working patch but underlying cause not yet known) (x86 build issues/patch splitup block research there)

Update1: https://88.198.106.157/pad/p/llvm-section-mismatch

Result: Added -mno-merge-globals

module unloading Completed JSM Module unloading is broken (minimally on x86_64)

Update: works on ARM

CC Stack Protector Completed Mark C Enabling CONFIG_CC_STACKPROTECTOR produces the following error:
arch/arm/boot/compressed/decompress.o: In function `zlib_inflate_table':
/rootdir/llvmlinux/targets/vexpress/src/linux/arch/arm/boot/compressed/\
../../../../lib/zlib_inflate/inftrees.c:315: undefined reference to `__stack_chk_fail'
/rootdir/llvmlinux/targets/vexpress/src/linux/arch/arm/boot/compressed/\
../../../../lib/zlib_inflate/inftrees.c:313: undefined reference to `__stack_chk_guard'
make[3]: *** [arch/arm/boot/compressed/vmlinux] Error 1)

Might be related to segment reference issues ?!

Update: retested 1/31/13 - no longer an issue for vexpress

(high priority)

GCC specific macros Completed Manuel S The uninitialized_var() macro is gcc dependent and does not work with clang:
#define uninitialized_var(x) x = x

Clang supports the following:

#define uninitialized_var(x) x = *(&x) 
GCC specific behavior Unassigned 4898 The compiler builtin __builtin_constant_p() must be allowed to fail.

BUILD_BUG_ON(!__builtin_constant_p(offset));

This fails for Clang and according to LLVM community arguement, should be allowed to fail. Clang can't determine this at parsing time due to the separation of the front end and back end of the compiler.

There is no clear way to implement the expected GCC behavior with clang but it is unclear if it is really needed in the first place.

(medium priority)

Clang warning flags Completed Mark C Need to add -Wunused-value if supported, to suppress enable warnings for all of the return values not assigned or cast as void. This option is disabled by default as it provides a overwhelming amount of warnings.

KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)

warning-1 += $(call cc-option, -Wunused-value)

Note: Now also fixed in LLVM Bug 13747

conditional infixes Completed Mark C Fix warning "conditional infixes are deprecated in unified syntax"

Seems to be a warning from gas (GNU assembler). It's inline assembly code from arch/arm/include/asm/uaccess.h

/* We use 33-bit arithmetic here... */
#define __range_ok(addr,size) ({ \
       unsigned long flag, roksum; \
       __chk_user_ptr(addr);   \
       __asm__("adds %1, %2, %3; sbcccs %1, %1, %0; movcc %0, #0" \
               : "=&r" (flag), "=&r" (roksum) \
               : "r" (addr), "Ir" (size), "0" (current_thread_info()->addr_limit) \
               : "cc"); \
       flag; })

Which ends up with clang inserting something like this into it's own ASM code which gas then doesn't like.

adds r5, r1, #4; sbcccs r5, r5, r4; movcc r4, #0

This is a problem with the Linux ARM code, not with Clang nor gas.

(medium priority)

Ftrace return_address Completed Mark C The declaration of return_address in ftrace and the later implementaion is GNU89 only (non C99 compliant GCC feature)

extern inline void *return_address(unsigned int)

needs to be:

extern inline __attribute__((gnu_inline)) void *return_address(unsigned int level)

Linux Kernel Issues Specific to ARM

0ARM Kernel Issues: 1 (100%)1
ARM Kernel Issues
Name Status Assigned BugID Description
kallsyms data Completed Mark C When enabling more config options, ARM produced the following error:
/bin/sh /rootdir/llvmlinux/targets/vexpress/src/linux/scripts/mksysmap  .tmp_System.map
cmp -s System.map .tmp_System.map || (echo Inconsistent kallsyms data; \
echo This is a bug - please report about it; echo Try "make KALLSYMS_EXTRA_PASS=1" as a workaround; \
rm .tmp_kallsyms* ; /bin/false )
Inconsistent kallsyms data
This is a bug - please report about it
Try make KALLSYMS_EXTRA_PASS=1 as a workaround
make[1]: *** [vmlinux] Error 1

This seems to not be an LLVM/Clang issue. See this thread.

Changed common/arm/bin/make-kernel.sh:

$MAKE CONFIG_DEBUG_SECTION_MISMATCH=y ARCH=arm CONFIG_DEBUG_INFO=1 \
CC="$CC_FOR_BUILD" HOSTCC=$HOSTCC_FOR_BUILD ${PARALLEL}

to

$MAKE KALLSYMS_EXTRA_PASS=1 CONFIG_DEBUG_SECTION_MISMATCH=y ARCH=arm CONFIG_DEBUG_INFO=1 \
CC="$CC_FOR_BUILD" HOSTCC=$HOSTCC_FOR_BUILD ${PARALLEL}

Linux Kernel Issues Specific to Raspberry Pi

0rpi Kernel Issues: 0 (0%)1
Kernel rpi Todos
Name Status Assigned Description
rpi usb/ethernet In Progress tinti USB still isn't working on Raspberry-pi. Need to track down issues with USB initialization. Raspberry Pi uses a SMSC95XX chip which is a USB hub with an Ethernet controller.

Recently, Jan-Simon discovered that khubd kernel thread is consuming a lot of CPU. We are debugging with KGDB.


Linux Kernel Issues Specific to MIPS

0MIPS Kernel Issues: 1 (50%)2
MIPS Kernel Issues
Name Status Assigned BugID Description
slab initialization Completed Slab memory allocator is not initialized correctly for Mips
I6400 fails to boot Unassigned I6400-specific: Kernel hangs after mounting RFS

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