Hello Masami Hiramatsu, Sorry for long delay, was out of town. >On Sun, Mar 27, 2022 at 11:55:26AM +0900, Masami Hiramatsu wrote: > Hi Padmanabha, > > On Sun, 27 Mar 2022 08:53:06 +0900 > Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > > > > > KNOWN ISSUE: > > > > According to the report from Padmanabha[3], the embedded bootconfig data may not > > be updated if you do incremental build the kernel with CONFIG_LTO. This is > > under investigation. > > I tried to test this version with LTO_CLANG_FULL and LTO_CLANG_THIN with > switching the embedded bootconfig file by CONFIG_EMBED_BOOT_CONFIG_FILE (on x86). > > I found that when I use LTO_CLANG_FULL, the embedded bootconfig was updated > correctly. > But with the LTO_CLANG_THIN, the embedded bootconfig was *NOT* updated. > > I used the latest prebuild llvm 15.0.0 on x86 [4]. Padmanabha, can you confirm > with this latest LLVM? I guess something wrong with your old LLVM. > > [4] https://download.01.org/0day-ci/cross-package/clang-latest/clang-latest/clang.tar.xz > Thanks for the link for prebuilt llvm 15.0.0. [p1] https://www.spinics.net/lists/kernel/msg4307362.html With llvm 15.0.0 and latest patchset v8 for bootconfig [p1] on arm64 the test observations are: For bootconfig: I dont observe anymore an issue with incremental builds, irresepctive of LTO type selected: FULL/THIN. For config.gz: The test observations is exactly similar to yours. With LTO_CLANG_THIN configs were *NOT* updated. But with LTO_CLANG_FULL confs were updated. Test results validates and confirms your earlier analysis on issue with inline asm and .incbin directive and THIN_LTO. > Here is the test procedure. > > 1. Prepare 2 different bootconfig files (bconf1, bconf2). > 2. Configure kernel with LTO_CLANG and setting the full path of bconf1 to > CONFIG_EMBED_BOOT_CONFIG_FILE. > 3. Build the kernel > 4. Boot the kernel with "bootconfig" in the kernel cmdline. > 5. Check the /proc/bootconfig is same as bconf1. > 6. Reconfigure kernel with the full path of *bconf2* to CONFIG_EMBED_BOOT_CONFIG_FILE. > 7. Rebuild the kernel (no cleanup) > 8. Boot the kernel with "bootconfig" in the kernel cmdline. > 9. Check the /proc/bootconfig is same as bconf2. > > So with LTO_CLANG_FULL, at the step 9 /proc/bootconfig shows bconf2, but with > LTO_CLANG_THIN, it shows bconf1. > > In both cases, build log showed that the default.bconf was updated (I confirmed the > lib/default.bconf is updated) > > UPD lib/default.bconf > CC lib/bootconfig.o > AR lib/lib.a > > > Here is my guess. I found that when we enable LTO_CLANG, the compiler compiles > C source file into LLVM IR bitcode. > > $ file work/linux/build-x86_64/lib/bootconfig.o > work/linux/build-x86_64/lib/bootconfig.o: LLVM IR bitcode > > This means at this point the object file doesn't include the lib/default.bconf > because it will be embedded by assembler. The bitcode seems only have the > inline asm code (which only has an .incbin directive) as a constatns block[5]. > > [5] > Block ID #11 (CONSTANTS_BLOCK): > Num Instances: 32 > Total Size: 54305b/6788.12B/1697W > Percent of file: 19.9792% > Average Size: 1697.03/212.13B/53W > Tot/Avg SubBlocks: 0/0.000000e+00 > Tot/Avg Abbrevs: 4/1.250000e-01 > Tot/Avg Records: 486/1.518750e+01 > Percent Abbrevs: 80.8642% > > Record Histogram: > Count # Bits b/Rec % Abv Record Kind > 219 4860 22.2 100.00 INTEGER > 144 1728 12.0 100.00 SETTYPE > 41 656 16.0 NULL > 39 2970 76.2 CE_INBOUNDS_GEP > 26 3504 134.8 100.00 CSTRING > 10 37720 3772.0 INLINEASM > 4 96 24.0 100.00 CE_CAST > 1 58 CE_CMP > 1 52 CE_SELECT > 1 46 CE_BINOP > > And when the LLVM runs LTO with THIN mode, it might not update (not rebuild to > machine code) that inline asm code block because that block is not updated. > I confirmed that the block (bootconfig.o) is not updated after rebuilding > the kernel as below. > Yes, thanks for details. Analysis is in sync with observations from test results. Thanks and Regards, Padmanabha.S > After step 3. > $ llvm-bcanalyzer work/linux/build-x86_64/lib/bootconfig.o > bconf.dump1 > After step 7. > $ llvm-bcanalyzer work/linux/build-x86_64/lib/bootconfig.o > bconf.dump2 > $ diff bconf.dump* > (No difference) > > Thank you, > > > > > [3] https://lore.kernel.org/all/20220321183500.GA4065@pswork/T/#u > > > > Thank you, > > > > --- > > > > Masami Hiramatsu (3): > > bootconfig: Check the checksum before removing the bootconfig from initrd > > bootconfig: Support embedding a bootconfig file in kernel > > docs: bootconfig: Add how to embed the bootconfig into kernel > > > > > > Documentation/admin-guide/bootconfig.rst | 30 ++++++++++++++++++++++++++--- > > include/linux/bootconfig.h | 10 ++++++++++ > > init/Kconfig | 21 ++++++++++++++++++++ > > init/main.c | 31 +++++++++++++++--------------- > > lib/.gitignore | 1 + > > lib/Makefile | 10 ++++++++++ > > lib/bootconfig.c | 23 ++++++++++++++++++++++ > > 7 files changed, 108 insertions(+), 18 deletions(-) > > > > -- > > Masami Hiramatsu (Linaro) <mhiramat@xxxxxxxxxx> > > > -- > Masami Hiramatsu <mhiramat@xxxxxxxxxx>
