Bug#886506: busybox sh broken on i386 with glibc 2.26, leads to kernel panic
On Sun, Jan 21, 2018 at 12:18 PM, Aurelien Jarno <aurel32@debian.org> wrote:
> On 2018-01-21 00:47, Ben Hutchings wrote:
>> On Wed, 17 Jan 2018 12:31:06 +0100 Aurelien Jarno <aurel32@debian.org> wrote:
>> [...]
>> > busybox is compiled with -mpreferred-stack-boundary=2 on i386 which has
>> > the same effect of reducing the default stack alignment from 16 bytes to
>> > 2 bytes. This comes from arch/i386/Makefile:
>>
>> The argument is the log2 of the alignment, so this sets alignment to 4
>> bytes - which is compliant with the System V psABI for i386.
>
> This is correct, but it is not compliant with the i386 GCC ABI which
> assumes the stack is 16-byte aligned (not just 4-byte aligned) when the
> call instruction in the caller was executed.
gcc people simply broke ABI just because they could. There were other ways
to accomodate SSE alignment restrictions, such as aligning stack
only in functions which spill vector temporaries to stack,
but gcc chose a disruptive one.
The breakage appears *now* because SSE vector usage inside glibc is increasing.
If your libc is careful to not use SSE needlessly, it would work fine.
As to how to fix this for busybox, let's have a config option to disable it.
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