From: Paul Burton <paul.burton@mips.com>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>,
Paul Burton <pburton@wavecomp.com>,
James Hogan <jhogan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"clang-built-linux@googlegroups.com"
<clang-built-linux@googlegroups.com>,
Nathan Chancellor <natechancellor@gmail.com>,
"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>
Subject: Re: [PATCH 1/5] MIPS: Don't use bc_false uninitialized in __mm_isBranchInstr
Date: Mon, 12 Aug 2019 04:47:15 +0000 [thread overview]
Message-ID: <MWHPR2201MB127785F4CEC464CB6F11F3DAC1D30@MWHPR2201MB1277.namprd22.prod.outlook.com> (raw)
In-Reply-To: <20190812033120.43013-2-natechancellor@gmail.com>
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 <natechancellor@gmail.com>
> Signed-off-by: Paul Burton <paul.burton@mips.com>
Thanks,
Paul
[ This message was auto-generated; if you believe anything is incorrect
then please email paul.burton@mips.com to report it. ]
next prev parent reply other threads:[~2019-08-12 4:47 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-12 3:31 [PATCH 0/5] Clang build fixes for MIPS Nathan Chancellor
2019-08-12 3:31 ` [PATCH 1/5] MIPS: Don't use bc_false uninitialized in __mm_isBranchInstr Nathan Chancellor
2019-08-12 4:47 ` Paul Burton [this message]
2019-08-12 3:31 ` [PATCH 2/5] MIPS/ptrace: Update mips_get_syscall_arg's return type Nathan Chancellor
2019-08-12 4:47 ` Paul Burton
2019-08-12 3:31 ` [PATCH 3/5] lib/mpi: Fix for building for MIPS32 with Clang Nathan Chancellor
2019-08-12 5:23 ` Nathan Chancellor
2019-08-12 5:26 ` Nathan Chancellor
2019-08-12 12:28 ` Herbert Xu
2019-08-12 17:58 ` Paul Burton
2019-08-12 7:35 ` Jussi Kivilinna
2019-08-12 17:14 ` Nathan Chancellor
2019-08-12 19:40 ` Jussi Kivilinna
2019-08-12 19:45 ` Nathan Chancellor
2019-08-12 3:31 ` [PATCH 4/5] lib/mpi: Fix for building for MIPS64 " Nathan Chancellor
2019-08-12 5:25 ` Nathan Chancellor
2019-08-12 17:42 ` Nick Desaulniers
2019-08-12 17:45 ` Nathan Chancellor
2019-08-12 3:31 ` [PATCH 5/5] MIPS: tlbex: Explicitly cast _PAGE_NO_EXEC to a boolean Nathan Chancellor
2019-08-12 4:47 ` Paul Burton
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