Re: [PATCH v2] x86: fix early boot crash on gcc-10

[Michael Matz]

Hello,

On Wed, 22 Apr 2020, Martin LiÅka wrote:

> One possible solution can be usage of a GCC pragma that will disable the
> tail-call optimization:
> 
> $ cat tail.c
> int foo(int);
> 
> #pragma GCC push_options
> #pragma GCC optimize("-fno-optimize-sibling-calls")

As we determined upthread (and the reason why we even still have this 
thread): the optimize attribute (and pragma) reset flags from the command 
line (the case in point was -fno-omit-frame-pointer).  So, that's not a
solution for now.

> And as I talked to Boris, I would recommend to come up with a 
> "configure" check that a compiler does not optimize the key code 
> sequence:

Right.  I think the traditional asm (i.e. one without operands) is good 
enough for the forseeable future from GCCs side: it relies on documented 
behaviour of traditional asms, and hence would be very hard to change.


Ciao,
Michael.