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prog: some bitfields are laid out incorrectly #1542

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dvyukov opened this issue Dec 13, 2019 · 0 comments
Closed

prog: some bitfields are laid out incorrectly #1542

dvyukov opened this issue Dec 13, 2019 · 0 comments
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dvyukov commented Dec 13, 2019 •
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See a5c1ab0. We lay out all these bitfields incorrectly and there are precedents in linux descriptions where such bitfields are used.
dvyukov added a commit that referenced this issue Dec 13, 2019
@dvyukov
sys/test: add more tests for bitfields
a5c1ab0 
Add tests for issue #1542

The correct results are obtained with the following program:

struct foo {
	unsigned char	f0;
	unsigned int	f1:4;
	unsigned short	f2:4;
};

struct bar {
	char f0;
	struct foo foo;
};

int main() {
	struct bar y;
	memset(&y, 0, sizeof(y));
	y.f0 = 0x12;
	y.foo.f0 = 0x34;
	y.foo.f1 = 0x56;
	y.foo.f2 = 0x78;
	int i;
	for (i = 0; i < sizeof(y); i++)
		printf("%02x", ((unsigned char*)&y)[i]);
	printf("\n");
}
@dvyukov dvyukov added the bug label Dec 13, 2019
dvyukov added a commit to dvyukov/syzkaller that referenced this issue Dec 17, 2019
@dvyukov
tools/syz-check: add description checking utility
3cf2eb3 
syz-check parses vmlinux dwarf, extracts struct descriptions,
compares them with what we have (size, fields, alignment, etc)
and produces .warn files.
This is first raw version, it can be improved in a number of ways.
But it already helped to identify a critical issue google#1542
and shows some wrong struct descriptions.

Update google#590
dvyukov added a commit that referenced this issue Dec 17, 2019
@dvyukov
tools/syz-check: add description checking utility
64ca0a3 
syz-check parses vmlinux dwarf, extracts struct descriptions,
compares them with what we have (size, fields, alignment, etc)
and produces .warn files.
This is first raw version, it can be improved in a number of ways.
But it already helped to identify a critical issue #1542
and shows some wrong struct descriptions.

Update #590
dvyukov added a commit that referenced this issue Dec 18, 2019
@dvyukov
sys/test: add few other tests for tricky bitfields
52395b6 
Update #1542
dvyukov added a commit that referenced this issue Dec 19, 2019
@dvyukov
sys/test: and another bitfield test
e30cbda 
Just trying to get my head around it (and fix this in tests).

Update #1542
@dvyukov dvyukov reopened this Dec 20, 2019
dvyukov added a commit that referenced this issue Dec 20, 2019
@dvyukov
pkg/compiler: refactor struct layout
9be5bbc 
Combine markBitfields and addAlignment functions.
Fixing #1542 will require doing both at the same time,
they are not really independent.
Also remove the special case for packed structs,
pad them as part of the common procedure.
No functional changes.
dvyukov added a commit that referenced this issue Dec 20, 2019
@dvyukov
sys/test: and another set of bitfield tests
08f0467 
Just trying to get my head around it (and fix this in tests).

Update #1542
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