On Fri, Jan 22, 2021 at 2:43 AM Nick Desaulniers <ndesaulni...@google.com> wrote: > > On Wed, Jan 20, 2021 at 6:03 PM Sedat Dilek <sedat.di...@gmail.com> wrote: > > > > On Mon, Jan 18, 2021 at 10:56 PM Bill Wendling <mo...@google.com> wrote: > > > > > > On Mon, Jan 18, 2021 at 9:26 AM Sedat Dilek <sedat.di...@gmail.com> wrote: > > > > > > > > On Mon, Jan 18, 2021 at 1:39 PM Sedat Dilek <sedat.di...@gmail.com> > > > > wrote: > > > > > > > > > > On Mon, Jan 18, 2021 at 3:32 AM Bill Wendling <mo...@google.com> > > > > > wrote: > > > > > > > > > > > > On Sun, Jan 17, 2021 at 4:27 PM Sedat Dilek <sedat.di...@gmail.com> > > > > > > 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? > > I was able to build+boot with LLVM_IAS=1 on my personal laptop (no > dwarf 5, just mainline+v5). >
To clarify: I can build a PGO-enabled Linux-kernel and boot it. Afterwards generate a vmlinux.profdata. In a next step: A rebuild without PGO-Kconfig disabled + LLVM_IAS=1 does not boot. - Sedat - > > > > 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. > > I agree, providing test results with patches that haven't landed yet > can cloud the interpretation of results. It would be helpful to drop > local patch sets before trying this. > > If the resulting image still isn't working for you, can you please > provide your config? Surely we'd be able to reproduce boot failures in > QEMU? Nothing comes to mind about a change of assemblers causing an > issue; I would assume assembly cannot be instrumented by the compiler > (even though the compiler is the "driver" of the assembler). > > The hash warnings are certainly curious. > IndexedInstrProfReader::getInstrProfRecord() is the only place in LLVM > sources that can emit that. > -- > Thanks, > ~Nick Desaulniers
