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Michael Ellerman 78f0929884 powerpc/64: Always build with 128-bit long double 
The amdgpu driver builds some of its code with hard-float enabled,
whereas the rest of the kernel is built with soft-float.

When building with 64-bit long double, if soft-float and hard-float
objects are linked together, the build fails due to incompatible ABI
tags.

In the past there have been build errors in the amdgpu driver caused by
this, some of those were due to bad intermingling of soft & hard-float
code, but those issues have now all been fixed since commit 58ddbecb14
("drm/amd/display: move remaining FPU code to dml folder").

However it's still possible for soft & hard-float objects to end up
linked together, if the amdgpu driver is built-in to the kernel along
with the test_emulate_step.c code, which uses soft-float. That happens
in an allyesconfig build.

Currently those build errors are avoided because the amdgpu driver is
gated on 128-bit long double being enabled. But that's not a detail the
amdgpu driver should need to be aware of, and if another driver starts
using hard-float the same problem would occur.

All versions of the 64-bit ABI specify that long-double is 128-bits.
However some compilers, notably the kernel.org ones, are built to use
64-bit long double by default.

Apart from this issue of soft vs hard-float, the kernel doesn't care
what size long double is. In particular the kernel using 128-bit long
double doesn't impact userspace's ability to use 64-bit long double, as
musl does.

So always build the 64-bit kernel with 128-bit long double. That should
avoid any build errors due to the incompatible ABI tags. Excluding the
code that uses soft/hard-float, the vmlinux is identical with/without
the flag.

It does mean any code which is incorrectly intermingling soft &
hard-float code will build without error, so those bugs will need to be
caught by testing rather than at build time.

For more background see:
  - commit d11219ad53 ("amdgpu: disable powerpc support for the newer display engine")
  - commit c653c59178 ("drm/amdgpu: Re-enable DCN for 64-bit powerpc")
  - https://lore.kernel.org/r/dab9cbd8-2626-4b99-8098-31fe76397d2d@app.fastmail.com

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Link: https://msgid.link/20230404102847.3303623-1-mpe@ellerman.id.au
History 2023-04-11 23:13:11 +10:00
arch powerpc/64: Always build with 128-bit long double 2023-04-11 23:13:11 +10:00
block block, bfq: fix uaf for 'stable_merge_bfqq' 2023-03-08 07:34:50 -07:00
certs Kbuild updates for v6.3 2023-02-26 11:53:25 -08:00
crypto Networking changes for 6.3. 2023-02-21 18:24:12 -08:00
Documentation Bug fixes and regressions for ext4, the most serious of which is a 2023-03-12 08:55:55 -07:00
drivers powerpc/64: Always build with 128-bit long double 2023-04-11 23:13:11 +10:00
fs Fixes for 6.3-rc1: 2023-03-12 09:47:08 -07:00
include Bug fixes and regressions for ext4, the most serious of which is a 2023-03-12 08:55:55 -07:00
init Kbuild updates for v6.3 2023-02-26 11:53:25 -08:00
io_uring io_uring: silence variable ‘prev’ set but not used warning 2023-03-09 10:10:58 -07:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel kernel.fork.v6.3-rc2 2023-03-12 09:04:28 -07:00
lib cpumask: re-introduce constant-sized cpumask optimizations 2023-03-05 14:30:34 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm: avoid gcc complaint about pointer casting 2023-03-04 14:03:27 -08:00
net wifi: cfg80211: Partial revert "wifi: cfg80211: Fix use after free for wext" 2023-03-12 16:21:59 -07:00
rust Rust fixes for 6.3-rc1 2023-03-03 14:51:15 -08:00
samples LoongArch changes for v6.3 2023-03-01 09:27:00 -08:00
scripts Remove Intel compiler support 2023-03-05 10:49:37 -08:00
security capability: just use a 'u64' instead of a 'u32[2]' array 2023-03-01 10:01:22 -08:00
sound sound fixes for 6.3-rc1 2023-03-04 10:53:59 -08:00
tools selftests/powerpc: Make dd output quiet 2023-03-30 23:35:43 +11:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM/riscv changes for 6.3 2023-02-15 12:33:28 -05:00
.clang-format cpumask: re-introduce constant-sized cpumask optimizations 2023-03-05 14:30:34 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for *.dtso files 2023-02-26 15:28:23 +09:00
.gitignore .gitignore: ignore *.cover and *.mbx 2023-02-05 18:51:22 +09:00
.mailmap drm fixes for 6.3-rc2 2023-03-10 08:57:46 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS There is no particular theme here - mainly quick hits all over the tree. 2023-02-23 17:55:40 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS powerpc: Add myself to MAINTAINERS for Power VFIO support 2023-03-15 00:52:09 +11:00
Makefile Linux 6.3-rc2 2023-03-12 16:36:44 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.