https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83174
Bug ID: 83174
Summary: -Wvla-larger-than reports wrong VLA size in some cases
Product: gcc
Version: 7.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: hao.hou at utah dot edu
Target Milestone: ---
Created attachment 42725
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42725&action=edit
The preprocessed source code repoduce the bug
There's some cases that -Wvla-lager-than only warns mistakenly only when the
strlen result is used as allocation size when -O2 or higher is turned on
Example code:
extern void f(void* ptr);
extern char* s;
void good(void)
{
unsigned long long l = __builtin_strlen(s);
if(l < 4)
{
char b[l&2];
f(b);
}
}
void bad(void)
{
unsigned long long l = __builtin_strlen(s);
if(l < 4)
{
char b[l&3];
f(b);
}
}
Compiler arguments:
$ gcc-7 -Wvla-larger-than=0x1000000 -O3 -S -c db.c
db.c: In function ‘bad’:
db.c:18:8: warning: argument to variable-length array may be too large
[-Wvla-larger-than=]
char b[l&3];
^
db.c:18:8: note: limit is 16777216 bytes, but argument may be as large as
9223372036854775806
It only warns the function uses l&3 as the VLA size.
Compiler Version:
Using built-in specs.
COLLECT_GCC=gcc-7
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
7.1.0-10ubuntu1~16.04.york0'
--with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-7
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib
--with-target-system-zlib --enable-objc-gc=auto --enable-multiarch
--disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 7.1.0 (Ubuntu 7.1.0-10ubuntu1~16.04.york0)
