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Posted to commits@nuttx.apache.org by GitBox <gi...@apache.org> on 2022/10/10 14:40:21 UTC
[GitHub] [incubator-nuttx] fjpanag opened a new issue, #7274: Undefined behaviour within UBSAN.
fjpanag opened a new issue, #7274:
URL: https://github.com/apache/incubator-nuttx/issues/7274
It seems that there is undefined behaviour within UBSAN itself.
When it is triggered, it calls itself recursivelly, without limit, exhausting the stack.
The output I get is:
```
[10/10/22 14:25:58] [28] [ EMERG] ubsan_prologue: ================================================================================
[10/10/22 14:25:58] [28] [ EMERG] ubsan_prologue: UBSAN: shift-out-of-bounds in ubsan/ubsan.c:163:35
[10/10/22 14:25:58] [28] [ EMERG] ubsan_prologue: ================================================================================
[10/10/22 14:25:58] [28] [ EMERG] ubsan_prologue: UBSAN: shift-out-of-bounds in ubsan/ubsan.c:163:35
[10/10/22 14:25:58] [28] [ EMERG] ubsan_prologue: ================================================================================
[10/10/22 14:25:58] [28] [ EMERG] ubsan_prologue: UBSAN: shift-out-of-bounds in ubsan/ubsan.c:163:35
[10/10/22 14:25:58] [28] [ EMERG] ubsan_prologue: ================================================================================
[10/10/22 14:25:58] [28] [ EMERG] ubsan_prologue: UBSAN: shift-out-of-bounds in ubsan/ubsan.c:163:35
[10/10/22 14:25:58] [28] [ EMERG] ubsan_prologue: ================================================================================
```
*(And repeats several thousand times...)*
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[GitHub] [incubator-nuttx] fjpanag commented on issue #7274: Undefined behaviour within UBSAN.
Posted by GitBox <gi...@apache.org>.
fjpanag commented on issue #7274:
URL: https://github.com/apache/incubator-nuttx/issues/7274#issuecomment-1273644051
> So the following is UB?
Answering my own question, I think it is indeed UB, because `ulong_val` is cast to a signed type.
Changing it to the following seems to resolve the issue, but I would appreciate any input from @no1wudi .
```c
return (int64_t)(ulong_val << extra_bits >> extra_bits);
```
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[GitHub] [incubator-nuttx] xiaoxiang781216 closed issue #7274: Undefined behaviour within UBSAN.
Posted by GitBox <gi...@apache.org>.
xiaoxiang781216 closed issue #7274: Undefined behaviour within UBSAN.
URL: https://github.com/apache/incubator-nuttx/issues/7274
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[GitHub] [incubator-nuttx] xiaoxiang781216 commented on issue #7274: Undefined behaviour within UBSAN.
Posted by GitBox <gi...@apache.org>.
xiaoxiang781216 commented on issue #7274:
URL: https://github.com/apache/incubator-nuttx/issues/7274#issuecomment-1273586030
The only difference is that the new change pass "-fsanitize=undefined", not -fsanitize=undefined. Does this make the difference?
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[GitHub] [incubator-nuttx] xiaoxiang781216 commented on issue #7274: Undefined behaviour within UBSAN.
Posted by GitBox <gi...@apache.org>.
xiaoxiang781216 commented on issue #7274:
URL: https://github.com/apache/incubator-nuttx/issues/7274#issuecomment-1273611489
Could you provide a patch to strip out quote from option? Or wait @no1wudi take a look tomorrow.
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[GitHub] [incubator-nuttx] xiaoxiang781216 commented on issue #7274: Undefined behaviour within UBSAN.
Posted by GitBox <gi...@apache.org>.
xiaoxiang781216 commented on issue #7274:
URL: https://github.com/apache/incubator-nuttx/issues/7274#issuecomment-1273613383
Ok, anyway @no1wudi can take a look tomorrow.
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[GitHub] [incubator-nuttx] fjpanag commented on issue #7274: Undefined behaviour within UBSAN.
Posted by GitBox <gi...@apache.org>.
fjpanag commented on issue #7274:
URL: https://github.com/apache/incubator-nuttx/issues/7274#issuecomment-1273612261
No, the correct version seems to be **with** the quotes.
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[GitHub] [incubator-nuttx] fjpanag commented on issue #7274: Undefined behaviour within UBSAN.
Posted by GitBox <gi...@apache.org>.
fjpanag commented on issue #7274:
URL: https://github.com/apache/incubator-nuttx/issues/7274#issuecomment-1273437378
Hmm this is very odd.
By reverting specifically 32a21a1b6762081e2f925bc63b9daf61f5c8b15a, the problem goes away...
I get no UBSan warnings.
(Of course using the exact same flags: `-fsanitize=undefined`)
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[GitHub] [incubator-nuttx] fjpanag commented on issue #7274: Undefined behaviour within UBSAN.
Posted by GitBox <gi...@apache.org>.
fjpanag commented on issue #7274:
URL: https://github.com/apache/incubator-nuttx/issues/7274#issuecomment-1273630410
> Ok, anyway @no1wudi can take a look tomorrow.
Sure! Just adding my findings, in the hope that I will help.
The offending line seems to be:
```
return ((int64_t)ulong_val) << extra_bits >> extra_bits;
```
I printed the value of `extra_bits` and it is 0 at the time of the problem.
So the following is UB?
```
return ((int64_t)ulong_val) << 0 >> 0;
```
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[GitHub] [incubator-nuttx] fjpanag commented on issue #7274: Undefined behaviour within UBSAN.
Posted by GitBox <gi...@apache.org>.
fjpanag commented on issue #7274:
URL: https://github.com/apache/incubator-nuttx/issues/7274#issuecomment-1273424556
Forgot to mention, this is on simulator.
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[GitHub] [incubator-nuttx] fjpanag commented on issue #7274: Undefined behaviour within UBSAN.
Posted by GitBox <gi...@apache.org>.
fjpanag commented on issue #7274:
URL: https://github.com/apache/incubator-nuttx/issues/7274#issuecomment-1273600103
> The only difference is that the new change pass "-fsanitize=undefined", not -fsanitize=undefined. Does this make the difference?
Yes, you are correct.
When I use:
```
ifeq ($(CONFIG_SIM_UBSAN),y)
ARCHOPTIMIZATION += -fsanitize=undefined
else ifeq ($(CONFIG_MM_UBSAN_ALL),y)
ARCHOPTIMIZATION += -fsanitize=undefined
endif
```
I get no UBSan warnings at all.
When I use:
```
ifeq ($(CONFIG_SIM_UBSAN),y)
ARCHOPTIMIZATION += "-fsanitize=undefined"
else ifeq ($(CONFIG_MM_UBSAN_ALL),y)
ARCHOPTIMIZATION += "-fsanitize=undefined"
endif
```
I get some warnings, both for UBSan and my code.
So it seems like in the first case UBSan is not actually working.
Anyway, the original issue remains: UBSan fails itself.
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