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Unportable usage of bit fields #143

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akruis opened this issue Nov 5, 2017 · 1 comment
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Unportable usage of bit fields #143

akruis opened this issue Nov 5, 2017 · 1 comment
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2.7-slp 3.5-slp 3.6-slp bug main-slp minor stackless python
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v3.6.x-slp

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akruis commented Nov 5, 2017

The "flags" member of Stackless tasklets and channels is a bit-field structure (PyTaskletFlagStruc and PyChannelFlagStruc). The methods tasklet_new, channel_new, tasklet_reduce, channel_reduce, tasklet_setstate and channel_setstate access the "flags" structure in an undefined (strict aliasing violation) or implementation defined way. Using bit-fields in a portable way is difficult and has been discussed widely. In short: placement of bit-field members in the storage unit is implementation defined. For details consult the language definition.

My fix will default to a slow but portable solution with the option to use the native memory layout, if we know that the compiler uses the conventional placement (first member starts at the least significant bit of the storage unit, other members follows immediately). Currently I know that x86 and amd64 are safe.
@akruis akruis added this to the v3.6.x-slp milestone Nov 5, 2017
akruis pushed a commit that referenced this issue Nov 5, 2017
Stackless issue #143: fix non-portable usage of bit fields #143
b9c243a 
- avoid type punning / strict aliasing violations
- don't rely on implementation defined placement of bit-fields in the
storage unit.
akruis pushed a commit that referenced this issue Nov 5, 2017
Stackless issue #143: fix non-portable usage of bit fields #143
4f9d807 
- avoid type punning / strict aliasing violations
- don't rely on implementation defined placement of bit-fields in the
storage unit.
(cherry picked from commit b9c243a)
akruis pushed a commit that referenced this issue Nov 5, 2017
Stackless issue #143: fix non-portable usage of bit fields
959abe1 
- avoid type punning / strict aliasing violations
- don't rely on implementation defined placement of bit-fields in the
storage unit.

(cherry picked from commit 5512131)
akruis pushed a commit that referenced this issue Nov 5, 2017
Stackless issue #143: fix non-portable usage of bit fields
5512131 
- avoid type punning / strict aliasing violations
- don't rely on implementation defined placement of bit-fields in the
storage unit.
(cherry picked from commit b9c243a)
@akruis akruis self-assigned this Nov 5, 2017
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akruis commented Nov 5, 2017

Fixed. I had to backport the macro Py_BUILD_ASSERT_EXPR(cond) from 3.x to 2.7.

@akruis akruis closed this as completed Nov 5, 2017
akruis pushed a commit that referenced this issue Dec 21, 2017
Stackless issue #145: fix test_doctest
7327e4b 
Stackless contributes two tests to builtins: TaskletExit and
TaskletExit.__init__. Therefore we have to adjust the limit.

Add missing changelog entries (#143, #144).
akruis pushed a commit that referenced this issue Dec 21, 2017
Stackless issue #145: fix test_doctest
8d02cf8 
Stackless contributes two tests to builtins: TaskletExit and
TaskletExit.__init__. Therefore we have to adjust the limit.

Add missing changelog entries (#143, #144).

(cherry picked from commit 7327e4b)
akruis pushed a commit that referenced this issue Dec 21, 2017
Stackless issue #145: fix test_doctest
0c66149 
Stackless contributes two tests to builtins: TaskletExit and
TaskletExit.__init__. Therefore we have to adjust the limit.

Add missing changelog entries (#143, #144).

(cherry picked from commit 7327e4b)
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