[U-Boot] [PATCH v3 3/6] arm: provide a PCS-compliant setjmp implementation

[Alexander Graf <agraf@suse.de>]

On 21.09.17 10:19, Philipp Tomsich wrote:
> The previous setjmp-implementation (as a static inline function that
> contained an 'asm volatile' sequence) was extremely fragile: (some
> versions of) GCC optimised the set of registers.  One critical example
> was the removal of 'r9' from the clobber list, if -ffixed-reg9 was
> supplied.

I wouldn't call that fragile, but "works as intended". Gcc only saves 
the registers it really needs to save - and if r9 is fixed it can safely 
assume that between setjmp/longjmp it did not change.

Did you encounter other cases where it did something wrong?

> To increase robustness and ensure PCS-compliant behaviour, the setjmp
> and longjmp implementation are now in assembly and closely match what
> one would expect to find in a libc implementation.

I'm personally quite indifferent on which version we take, but I 
personally found the inline asm version more readable. At least it was 
half-way self-documenting and struct offset independent ;).

But again, I really don't have strong feelings. I only wrote the inline 
asm version because we didn't have any implementation at all. If you opt 
to maintain yours, be my guest :).


Alex