https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70188
Bug ID: 70188
Summary: gcc 4.9+ miscompiles code on hppa
Product: gcc
Version: 4.9.4
URL: https://patchwork.kernel.org/patch/8402441/
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: deller at gmx dot de
CC: dave.anglin at bell dot net
Target Milestone: ---
Target: hppa64-linux-gnu-gcc
Linux kernels above 4.3 don't boot any longer when compiled with gcc-4.9 or
gcc-5.
After some analysis, it seems gcc miscompiles the function
blk_bio_segment_split() in block/blk-merge.c. Compiling this function with -O0
or -O1 does produce a functional Linux kernel, but when compiled with -O2 the
kernel crashes during SCSI detection.
I was able to extract the function from the kernel source and attached is a
preprocessed file for easier analysis. It seems the variables bvprv and/or
bvprvp get optimized out when compiled with -O2.
This command is used to compile the file:
hppa64-linux-gnu-gcc-4.9 -Wp,-MD,block/.blk-merge_part.o.d -nostdinc -isystem
/usr/lib/gcc/hppa64-linux-gnu/4.9/include
-I/build/linux/linux-4.4.4/arch/parisc/include
-Iarch/parisc/include/generated/uapi -Iarch/parisc/include/generated
-I/build/linux/linux-4.4.4/include -Iinclude
-I/build/linux/linux-4.4.4/arch/parisc/include/uapi
-Iarch/parisc/include/generated/uapi -I/build/linux/linux-4.4.4/include/uapi
-Iinclude/generated/uapi -include
/build/linux/linux-4.4.4/include/linux/kconfig.h
-I/build/linux/linux-4.4.4/block -Iblock -D__KERNEL__ -Wall -Wundef
-Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common
-Werror-implicit-function-declaration -Wno-format-security -std=gnu89 -pipe
-mno-space-regs -mdisable-fpregs -ffunction-sections -march=2.0 -mschedule=8000
-fno-delete-null-pointer-checks -O2 --param=allow-store-data-races=0
-Wframe-larger-than=2048 -fno-stack-protector -Wno-unused-but-set-variable
-fno-omit-frame-pointer -fno-optimize-sibling-calls
-fno-var-tracking-assignments -Wdeclaration-after-statement -Wno-pointer-sign
-fno-strict-overflow -fconserve-stack -Werror=implicit-int
-Werror=strict-prototypes -Werror=date-time -DCC_HAVE_ASM_GOTO
-fno-cse-follow-jumps -D"KBUILD_STR(s)=#s"
-D"KBUILD_BASENAME=KBUILD_STR(blk_merge_part)"
-D"KBUILD_MODNAME=KBUILD_STR(blk_merge_part)" -c -o block/.tmp_blk-merge_part.o
/build/linux/linux-4.4.4/block/blk-merge_part.c
