https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92904
Bug ID: 92904
Summary: GCC generates movdqa instructions to unaligned memory
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: jesse.huard at dellteam dot com
Target Milestone: ---
Created attachment 47467
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47467&action=edit
Preprocessed test source file for reproducing the issue.
Compiling the attached test program on x86_64 with optimisations enabled
produces code which segfaults in a movdqa instruction accessing unaligned
memory. This was observed in code which passes an unsigned __int128 as a
variadic function argument when we attempt to retrieve the argument with
va_arg().
movdqa is expecting a 16-byte aligned memory location, but instead we get an
unaligned address on the stack pointing to our variadic argument within the
va_list's reg_save_area. This results in a segmentation fault.
12 b = va_arg(args, unsigned __int128);
0x000055555555517b <+50>: movl $0x18,(%rsp)
=> 0x0000555555555182 <+57>: movdqa 0x28(%rsp),%xmm0 # segfault
here!
0x0000555555555188 <+63>: movaps %xmm0,0x2ec1(%rip) #
0x555555558050 <b>
(gdb) p $rsp+0x28
$1 = (void *) 0x7fffffffe2d8
(gdb) p args
$2 = {{gp_offset = 24, fp_offset = 0, overflow_arg_area = 0x7fffffffe310,
reg_save_area = 0x7fffffffe2d0}}
Compiler invocation:
gcc -g -O1 test.c -o test
GCC information:
$ 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)
libc information:
$ /usr/lib/libc.so.6
GNU C Library (GNU libc) stable release version 2.30.
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 9.2.0.
libc ABIs: UNIQUE IFUNC ABSOLUTE
