Hello,
Nathan Chancellor wrote:
> 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.
Applied to mips-next.
> commit c2869aafe719
> https://git.kernel.org/mips/c/c2869aafe719
>
> 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 <natechancel...@gmail.com>
> Signed-off-by: Paul Burton <paul.bur...@mips.com>
Thanks,
Paul
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