[PATCH 2/3] ARM: convert to generated system call tables

Geert Uytterhoeven [off-list ref] writes:

On Sat, Oct 22, 2016 at 10:23 PM, Robert Jarzmik [off-list ref] wrote:

quoted

Arnd Bergmann [off-list ref] writes:

quoted

On Friday, October 21, 2016 4:48:56 PM CEST Russell King - ARM Linux wrote:

quoted

What's the point of the x32 mode?

On x86, the motivation is faster code for most use cases that
don't need a lot of memory, as the 64-bit opcodes have 16 registers
rather than 8 in 32-bit mode but 32-bit pointers have lower
cache footprint than 64-bit pointers.

For completness, the second point of x32 AFAIU is the IP-relative addressing
which is not available in standard 32 bit mode, which improves PIC code. For
simple not algorithmic code (think Android HAL for example) with many shared
libraries, it's better in the Hardware Abstraction Layer Libraries, instead of
the push-to-stack and pop register.

But that's not an advantage compared to full am64 mode, right?

Nope, the amd64 (that's what you have in mind with am64, not aarch64 right ?)
mode has the IP-relative has well, so x32 has no advantage over amd64 in this
area.

x32 over amd64 advantage is cache and memory footprint AFAICT, I don't see other
benefits. There doesn't seem to be any ISA differences, or I didn't really
notice in my daily system performance analysis job.

There was a nice presentation made by Peter Anvin at a Plumber conference, here
: http://linuxplumbersconf.org/2011/ocw/sessions/531

Cheers.

-- 
Robert