https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93302
Bug ID: 93302
Summary: -O2 -fno-inline produces wrong results
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: lifeibiren at gmail dot com
Target Milestone: ---
Created attachment 47665
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47665&action=edit
preprocessed file
I am code to do tcp checksum and find that output binary doesn't work as
expected with compilation option -O2 -fno-inline.
Partial source code is uploaded as an attachment and it seems to work with any
compilation options but -O2 -fno-inline.
Test Env:
gcc 9.2.0 (Arch Linux)
gcc 5.3.0 (Ubuntu 16.04)
Expected output:
12345678 87654321 40 12
5678 5678
1234 68ac
4321 abcd
8765 13332
600 13932
2800 16132
I disassemble the output binary and find that the instructions to store saddr
and daddr to stack memory are optimized out so hdr's first two members stay
uninitialized.
If a memory barrier 'asm volatile("": : :"memory");' is put before access
'hdr', gcc could get it right.
Env Info:
GCC VERSION:
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib
--libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++,d --enable-shared
--enable-threads=posix --with-system-zlib --with-isl --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch
--disable-libssp --enable-gnu-unique-object --enable-linker-build-id
--enable-lto --enable-plugin --enable-install-libiberty
--with-linker-hash-style=gnu --enable-gnu-indirect-function --enable-multilib
--disable-werror --enable-checking=release --enable-default-pie
--enable-default-ssp --enable-cet=auto gdc_include_dir=/usr/include/dlang/gdc
Thread model: posix
gcc version 9.2.0 (GCC)
BUG COMMAND:
$ gcc test3.c -O2 -fno-inline
COMPILER OUTPUT:
NOTHING
OS:
$ cat /etc/issue
Arch Linux \r (\l)
PREP FILE:
ATTACHMENT
