On Mon, Jan 18, 2021 at 10:56 PM Bill Wendling <morbo@xxxxxxxxxx> wrote: > > On Mon, Jan 18, 2021 at 9:26 AM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote: > > > > On Mon, Jan 18, 2021 at 1:39 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote: > > > > > > On Mon, Jan 18, 2021 at 3:32 AM Bill Wendling <morbo@xxxxxxxxxx> wrote: > > > > > > > > On Sun, Jan 17, 2021 at 4:27 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote: > > > > > > > > > > [ big snip ] > > > > > > > > [More snippage.] > > > > > > > > > [ CC Fangrui ] > > > > > > > > > > With the attached... > > > > > > > > > > [PATCH v3] module: Ignore _GLOBAL_OFFSET_TABLE_ when warning for > > > > > undefined symbols > > > > > > > > > > ...I was finally able to boot into a rebuild PGO-optimized Linux-kernel. > > > > > For details see ClangBuiltLinux issue #1250 "Unknown symbol > > > > > _GLOBAL_OFFSET_TABLE_ loading kernel modules". > > > > > > > > > Thanks for confirming that this works with the above patch. > > > > > > > > > @ Bill Nick Sami Nathan > > > > > > > > > > 1, Can you say something of the impact passing "LLVM_IAS=1" to make? > > > > > > > > The integrated assembler and this option are more-or-less orthogonal > > > > to each other. One can still use the GNU assembler with PGO. If you're > > > > having an issue, it may be related to ClangBuiltLinux issue #1250. > > > > > > > > > 2. Can you please try Nick's DWARF v5 support patchset v5 and > > > > > CONFIG_DEBUG_INFO_DWARF5=y (see attachments)? > > > > > > > > > I know Nick did several tests with PGO. He may have looked into it > > > > already, but we can check. > > > > > > > > > > Reproducible. > > > > > > LLVM_IAS=1 + DWARF5 = Not bootable > > > > > > I will try: > > > > > > LLVM_IAS=1 + DWARF4 > > > > > > > I was not able to boot into such a built Linux-kernel. > > > PGO will have no effect on debugging data. If this is an issue with > DWARF, then it's likely orthogonal to the PGO patch. > > > For me worked: DWARF2 and LLVM_IAS=1 *not* set. > > > > Of course, this could be an issue with my system's LLVM/Clang. > > > > Debian clang version > > 12.0.0-++20210115111113+45ef053bd709-1~exp1~20210115101809.3724 > > > Please use the official clang 11.0.1 release > (https://releases.llvm.org/download.html), modifying the > kernel/pgo/Kconfig as I suggested above. The reason we specify clang > 12 for the minimal version is because of an issue that was recently > fixed. > I downgraded to clang-11.1.0-rc1. ( See attachment. ) Doing the first build with PGO enabled plus DWARF5 and LLVM_IAS=1 works. But again after generating vmlinux.profdata and doing the PGO-rebuild - the resulting Linux-kernel does NOT boot in QEMU or on bare metal. With GNU/as I can boot. So this is independent of DWARF v4 or DWARF v5 (LLVM_IAS=1 and DWARF v2 is not allowed). There is something wrong (here) with passing LLVM_IAS=1 to make when doing the PGO-rebuild. Can someone please verify and confirm that the PGO-rebuild with LLVM_IAS=1 boots or boots not? Thanks. - Sedat - > > Can you give me a LLVM commit-id where you had success with LLVM_IAS=1 > > and especially CONFIG_DEBUG_INFO_DWARF5=y? > > Success means I was able to boot in QEMU and/or bare metal. > > > The DWARF5 patch isn't in yet, so I don't want to rely upon it too much. > > -bw
From a69dcc377c601525d8c760e7b20c5d06eaf1fe76 Mon Sep 17 00:00:00 2001 From: Sedat Dilek <sedat.dilek@xxxxxxxxx> Date: Tue, 19 Jan 2021 00:44:36 +0100 Subject: [PATCH] pgo: Allow to use clang >= v11.0.1 --- kernel/pgo/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/pgo/Kconfig b/kernel/pgo/Kconfig index 76a640b6cf6e..5fe9635ac64c 100644 --- a/kernel/pgo/Kconfig +++ b/kernel/pgo/Kconfig @@ -8,7 +8,7 @@ config PGO_CLANG bool "Enable clang's PGO-based kernel profiling" depends on DEBUG_FS depends on ARCH_SUPPORTS_PGO_CLANG - depends on CC_IS_CLANG && CLANG_VERSION >= 120000 + depends on CC_IS_CLANG && CLANG_VERSION >= 120000 || CLANG_VERSION >= 110001 help This option enables clang's PGO (Profile Guided Optimization) based code profiling to better optimize the kernel. -- 2.30.0
