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-Wsometimes-uninitialized in net/atm/resources.c #386

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nickdesaulniers opened this issue Feb 26, 2019 · 5 comments
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-Wsometimes-uninitialized in net/atm/resources.c #386

nickdesaulniers opened this issue Feb 26, 2019 · 5 comments
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@nathanchance
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-Wsometimes-uninitialized [ARCH] arm32 This bug impacts ARCH=arm [BUG] linux A bug that should be fixed in the mainline kernel. [FIXED][LINUX] 5.1 This bug was fixed in Linux 5.1

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@nickdesaulniers
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from #381

net/atm/resources.c:256:6: error: variable 'number' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
net/atm/resources.c:212:7: error: variable 'iobuf_len' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
@nickdesaulniers nickdesaulniers added good first issue Good for newcomers [BUG] linux A bug that should be fixed in the mainline kernel. low priority This bug is not critical and not a priority [ARCH] arm32 This bug impacts ARCH=arm -Wsometimes-uninitialized labels Feb 26, 2019
@nickdesaulniers
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This case looks trickier. Also, I don't get the same line numbers in my checkout of -next, so maybe that's making it hard to spot. The dual preprocessor and runtime check for compat is very odd.

@nickdesaulniers nickdesaulniers removed the good first issue Good for newcomers label Feb 26, 2019
@nathanchance
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Hmm odd... Here is the full warning:

net/atm/resources.c:256:6: warning: variable 'number' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
        if (compat) {
            ^~~~~~
net/atm/resources.c:283:47: note: uninitialized use occurs here
        dev = try_then_request_module(atm_dev_lookup(number), "atm-device-%d",
                                                     ^~~~~~
include/linux/kmod.h:41:4: note: expanded from macro 'try_then_request_module'
        ((x) ?: (__request_module(true, mod), (x)))
          ^
net/atm/resources.c:256:2: note: remove the 'if' if its condition is always false
        if (compat) {
        ^~~~~~~~~~~~~
net/atm/resources.c:199:24: note: initialize the variable 'number' to silence this warning
        int error, len, number, size = 0;
                              ^
                               = 0
net/atm/resources.c:212:7: warning: variable 'iobuf_len' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
                if (compat) {
                    ^~~~~~
net/atm/resources.c:227:21: note: uninitialized use occurs here
                if (get_user(len, iobuf_len))
                                  ^~~~~~~~~
arch/arm/include/asm/uaccess.h:237:23: note: expanded from macro 'get_user'
                __get_user_check(x, p);                                 \
                                    ^
arch/arm/include/asm/uaccess.h:197:50: note: expanded from macro '__get_user_check'
                register typeof(*(p)) __user *__p asm("r0") = (p);      \
                                                               ^
net/atm/resources.c:212:3: note: remove the 'if' if its condition is always false
                if (compat) {
                ^~~~~~~~~~~~~
net/atm/resources.c:204:23: note: initialize the variable 'iobuf_len' to silence this warning
        int __user *iobuf_len;
                             ^
                              = NULL
2 warnings generated.

My guess is it is one of those "Clang does analysis before optimization" because when CONFIG_COMPAT isn't set, compat is always 0 so the true case will never happen.

@nathanchance
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I'm not proud of this one: https://lore.kernel.org/lkml/20190307165741.19870-1-natechancellor@gmail.com/

@nathanchance nathanchance added [PATCH] Submitted A patch has been submitted for review and removed low priority This bug is not critical and not a priority labels Mar 7, 2019
@nathanchance nathanchance self-assigned this Mar 7, 2019
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Patch accepted: https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/?id=f9d19a7494e5341a7f256823e32788ae560ca22f

@nathanchance nathanchance added [PATCH] Accepted A submitted patch has been accepted upstream and removed [PATCH] Submitted A patch has been submitted for review labels Mar 7, 2019
fengguang pushed a commit to 0day-ci/linux that referenced this issue Mar 7, 2019
@nathanchance @davem330
net: atm: Use IS_ENABLED in atm_dev_ioctl
f9d19a7 
When building with -Wsometimes-uninitialized, Clang warns:

net/atm/resources.c:256:6: warning: variable 'number' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
net/atm/resources.c:212:7: warning: variable 'iobuf_len' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]

Clang won't realize that compat is 0 when CONFIG_COMPAT is not set until
the constant folding stage, which happens after this semantic analysis.
Use IS_ENABLED instead so that the zero is present at the semantic
analysis stage, which eliminates this warning.

Link: ClangBuiltLinux#386
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
fengguang pushed a commit to 0day-ci/linux that referenced this issue Mar 10, 2019
@nathanchance @intel-lab-lkp
net: atm: Use IS_ENABLED in atm_dev_ioctl
0222d9d 
When building with -Wsometimes-uninitialized, Clang warns:

net/atm/resources.c:256:6: warning: variable 'number' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
net/atm/resources.c:212:7: warning: variable 'iobuf_len' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]

Clang won't realize that compat is 0 when CONFIG_COMPAT is not set until
the constant folding stage, which happens after this semantic analysis.
Use IS_ENABLED instead so that the zero is present at the semantic
analysis stage, which eliminates this warning.

Link: ClangBuiltLinux#386
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
@nathanchance
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Merged into mainline (second was a follow up fix):

https://git.kernel.org/torvalds/c/f9d19a7494e5341a7f256823e32788ae560ca22f

https://git.kernel.org/torvalds/c/0805a4b894a8daaf76ad99934563d8ecfc6e7aed

@nathanchance nathanchance added [FIXED][LINUX] 5.1 This bug was fixed in Linux 5.1 and removed [PATCH] Accepted A submitted patch has been accepted upstream labels Mar 11, 2019
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-Wsometimes-uninitialized [ARCH] arm32 This bug impacts ARCH=arm [BUG] linux A bug that should be fixed in the mainline kernel. [FIXED][LINUX] 5.1 This bug was fixed in Linux 5.1
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