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. > > > 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. > That means to build the first PGO-enabled kernel with clang-11 and rebuild in a second step again with the same clang-11. Just FYI: I was able to boot into a Linux-kernel rebuild with *no LLVM_IAS=1* (means use "GNU AS 2.35.1") set and DWARF5 using LLVM=1 from LLVM/Clang-12. - Sedat -
