1. Feature Overview:
Feature Id: [66900]
a. Name of Feature: [6.1 FEAT] 64 bit register support in 31 bit emulation - Binutils
b. Feature Description
This feature provides a binutils extension marks binaries compiled with -m31 -mzarch with a flag in
the ELF header. This allows us to perform a run-time check in order to prevent such binaries from
being executed on kernels not providing the highgprs facility.

The intention is to mark binaries built with -m31 -mzarch with the EF_S390_HIGH_GPRS flag in the
e_flags field of the elf header.

Compiling code with -m31 -mzarch will in the future exploit the presence of 64 bit registers also in
32 bit applications. This requires the kernel to save/restore the upper halfs of 64 bit registers
and include these values in core dumps. For S/390 the Linux kernel supports that starting with
version 2.6.32 and indicates that fact in /proc/cpuinfo as "highgprs" and in the AT_HWCAPS field of
the auxiliary vector with the HWCAP_S390_HIGH_GPRS flag.

2. Feature Details:
Sponsor: LTC zSeries BOE
Architectures:
  zSeries - 31/32 compat, zSeries - 64 native, 

Arch Specificity: purely arch specific code
Affects Kernel Modules: Field does not exist
Delivery Mechanism: Backport
Category: other
Request Type: Toolchain - Enhancement from IBM
d. Upstream Acceptance: Field does not exist
Sponsor Priority P1
f. Severity: ship issue
IBM Confidential: No
Code Contribution: IBM code
g. Component Version Target:
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3. Business Case
ISVs and customers will benefit from major performance improvements and less cpu cost, which in turn
will result of more efficient usage of the System z HW and customer satisfaction.

4. Primary contact at Red Hat:
John Jarvis
jjarvis

5. Primary contacts at Partner:
Project Management Contact:
Hans-Georg Markgraf, mgrf.com

Technical contact(s):
Gonzalo Muelas Serrano, gmuelas.com