c2869aafe7
clang warns:
arch/mips/kernel/branch.c:148:8: error: variable 'bc_false' is used
uninitialized whenever switch case is taken
[-Werror,-Wsometimes-uninitialized]
case mm_bc2t_op:
^~~~~~~~~~
arch/mips/kernel/branch.c:157:8: note: uninitialized use occurs here
if (bc_false)
^~~~~~~~
arch/mips/kernel/branch.c:149:8: error: variable 'bc_false' is used
uninitialized whenever switch case is taken
[-Werror,-Wsometimes-uninitialized]
case mm_bc1t_op:
^~~~~~~~~~
arch/mips/kernel/branch.c:157:8: note: uninitialized use occurs here
if (bc_false)
^~~~~~~~
arch/mips/kernel/branch.c:142:4: note: variable 'bc_false' is declared
here
int bc_false = 0;
^
2 errors generated.
When mm_bc1t_op and mm_bc2t_op are taken, the bc_false initialization
does not happen, which leads to a garbage value upon use, as illustrated
below with a small sample program.
$ mipsel-linux-gnu-gcc --version | head -n1
mipsel-linux-gnu-gcc (Debian 8.3.0-2) 8.3.0
$ clang --version | head -n1
ClangBuiltLinux clang version 9.0.0 (git://github.com/llvm/llvm-project
544315b4197034a3be8acd12cba56a75fb1f08dc) (based on LLVM 9.0.0svn)
$ cat test.c
#include <stdio.h>
static void switch_scoped(int opcode)
{
switch (opcode) {
case 1:
case 2: {
int bc_false = 0;
bc_false = 4;
case 3:
case 4:
printf("\t* switch scoped bc_false = %d\n", bc_false);
}
}
}
static void function_scoped(int opcode)
{
int bc_false = 0;
switch (opcode) {
case 1:
case 2: {
bc_false = 4;
case 3:
case 4:
printf("\t* function scoped bc_false = %d\n", bc_false);
}
}
}
int main(void)
{
int opcode;
for (opcode = 1; opcode < 5; opcode++) {
printf("opcode = %d:\n", opcode);
switch_scoped(opcode);
function_scoped(opcode);
printf("\n");
}
return 0;
}
$ mipsel-linux-gnu-gcc -std=gnu89 -static test.c && \
qemu-mipsel a.out
opcode = 1:
* switch scoped bc_false = 4
* function scoped bc_false = 4
opcode = 2:
* switch scoped bc_false = 4
* function scoped bc_false = 4
opcode = 3:
* switch scoped bc_false = 2147483004
* function scoped bc_false = 0
opcode = 4:
* switch scoped bc_false = 2147483004
* function scoped bc_false = 0
$ clang -std=gnu89 --target=mipsel-linux-gnu -m32 -static test.c && \
qemu-mipsel a.out
opcode = 1:
* switch scoped bc_false = 4
* function scoped bc_false = 4
opcode = 2:
* switch scoped bc_false = 4
* function scoped bc_false = 4
opcode = 3:
* switch scoped bc_false = 2147483004
* function scoped bc_false = 0
opcode = 4:
* switch scoped bc_false = 2147483004
* function scoped bc_false = 0
Move the definition up so that we get the right behavior and mark it
__maybe_unused as it will not be used when CONFIG_MIPS_FP_SUPPORT
isn't enabled.
Fixes: 6a1cc218b9cc ("MIPS: branch: Remove FP branch handling when CONFIG_MIPS_FP_SUPPORT=n")
Link: https://github.com/ClangBuiltLinux/linux/issues/603
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: clang-built-linux@googlegroups.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.