Aurelien Jarno wrote:
Hi all,
Since version 4.3, gcc changed its behaviour concerning the x86/x86-64
ABI and the direction flag, that is it now assumes that the direction
flag is cleared at the entry of a function and it doesn't clear once
more if needed.
This causes some problems with the Linux kernel which does not clear
the direction flag when entering a signal handler. The small code below
(for x86-64) demonstrates that.
If the signal handler is using code that need the direction flag cleared
(for example bzero() or memset()), the code is incorrectly executed.
I guess this has to be fixed on the kernel side, but also gcc-4.3 could
revert back to the old behaviour, that is clearing the direction flag
when entering a routine that touches it until most people are running a
fixed kernel.
Linux should definitely follow the ABI. This is a bug, and a pretty
serious such.
-hpa
