On Thu, Jan 28, 2021 at 10:12 PM Nick Desaulniers
[off-list ref] wrote:

On Thu, Jan 28, 2021 at 12:46 PM Sedat Dilek [off-list ref] wrote:

quoted

[ LLVM ]

Today, I switched over to LLVM version 12.0.0-rc1.


[ Step #1: 5.11.0-rc5-5-amd64-clang12-pgo ]

My first kernel was built with CONFIG_PGO_CLANG=y and LLVM=1 plus LLVM_IAS=1.

[ start-build_5.11.0-rc5-5-amd64-clang12-pgo.txt ]
dileks    193090  193065  0 06:54 pts/2    00:00:00 /usr/bin/perf_5.10
stat make V=1 -j4 HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
LD=ld.lld LLVM=1 LLVM_IAS=1 PAHOLE=/opt/pahole/bin/pahole
LOCALVERSION=-5-amd64-clang12-pgo KBUILD_VERBOSE=1
KBUILD_BUILD_HOST=iniza KBUILD_BUILD_USER=sedat.dilek@gmail.com
KBUILD_BUILD_TIMESTAMP=2021-01-28 bindeb-pkg
KDEB_PKGVERSION=5.11.0~rc5-5~bullseye+dileks1

Config: config-5.11.0-rc5-5-amd64-clang12-pgo


[ Step #2: x86-64 defconfig & vmlinux.profdata ]

Booted into 5.11.0-rc5-5-amd64-clang12-pgo and built an x86-64
defconfig to generate/merge a vmlinux.profdata file.

[ start-build_x86-64-defconfig.txt ]
dileks     18430   15640  0 11:15 pts/2    00:00:00 make V=1 -j4
HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang LD=ld.lld LLVM=1
LLVM_IAS=1

Script: profile_clang-pgo.sh
Config: dot-config.x86-64-defconfig


[ Step #3.1: 5.11.0-rc5-6-amd64-clang12-pgo & GNU-AS ]

The first rebuild with CONFIG_PGO_CLANG=n and "LLVM=1
KCFLAGS=-fprofile-use=vmlinux.profdata".
I was able to boot into this one.
Used assembler: GNU-AS 2.35.1

[ start-build_5.11.0-rc5-6-amd64-clang12-pgo.txt ]
dileks     65734   65709  0 11:54 pts/2    00:00:00 /usr/bin/perf_5.10
stat make V=1 -j4 HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
LD=ld.lld PAHOLE=/opt/pahole/bin/pahole
LOCALVERSION=-6-amd64-clang12-pgo KBUILD_VERBOSE=1
KBUILD_BUILD_HOST=iniza KBUILD_BUILD_USER=sedat.dilek@gmail.com
KBUILD_BUILD_TIMESTAMP=2021-01-28 bindeb-pkg
KDEB_PKGVERSION=5.11.0~rc5-6~bullseye+dileks1 LLVM=1
KCFLAGS=-fprofile-use=vmlinux.profdata

Config: config-5.11.0-rc5-6-amd64-clang12-pgo


[ Step #3.2: 5.11.0-rc5-7-amd64-clang12-pgo & Clang-IAS ]

The second rebuild with CONFIG_PGO_CLANG=n and "LLVM=1
KCFLAGS=-fprofile-use=vmlinux.profdata" plus LLVM_IAS=1.
Compilable but NOT bootable in QEMU and on bare metal.
Used assembler: Clang-IAS v12.0.0-rc1

[ start-build_5.11.0-rc5-7-amd64-clang12-pgo.txt ]
dileks      6545    6520  0 16:31 pts/2    00:00:00 /usr/bin/perf_5.10
stat make V=1 -j4 HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
LD=ld.lld PAHOLE=/opt/pahole/bin/pahole
LOCALVERSION=-7-amd64-clang12-pgo KBUILD_VERBOSE=1
KBUILD_BUILD_HOST=iniza KBUILD_BUILD_USER=sedat.dilek@gmail.com
KBUILD_BUILD_TIMESTAMP=2021-01-28 bindeb-pkg
KDEB_PKGVERSION=5.11.0~rc5-7~bullseye+dileks1 LLVM=1
KCFLAGS=-fprofile-use=vmlinux.profdata LLVM_IAS=1

Config: config-5.11.0-rc5-7-amd64-clang12-pgo


[ Conclusion ]

The only statement I can tell you is a "PGO optimized" rebuild with
LLVM_IAS=1 is compilable but NOT bootable.

Thanks for the extensive testing and report. Can you compress, upload,
and post a link to your kernel image? I would like to take it for a
spin in QEMU and see if I can find what it's doing, then work
backwards from there.

Which files do you need?
For QEMU: bzImage and initrd.img enough?

- Sedat -