Hi. On Wed, 27 Jan 2021 at 14:06, Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote: > > Em Mon, Jan 25, 2021 at 01:06:21PM +0000, Giuliano Procida escreveu: > > Hi. > > > > This follows on from my change to improve the error handling around > > llvm-objcopy in libbtf.c. > > > > Note on recipients: Please let me know if I should adjust To or CC. > > > > Note on style: I've generally placed declarations as allowed by C99, > > closest to point of use. Let me know if you'd prefer otherwise. > > > > 1. Improve ELF error reporting > > applied > > > 2. Add .BTF section using libelf > > > > This shows the minimal amount of code needed to drive libelf. However, > > it leaves layout up to libelf, which is almost certainly not wanted. > > > > As an unexpcted side-effect, vmlinux is larger than before. It seems > > llvm-objcopy likes to trim down .strtab. > > We have to test this thoroughly, I'm adding support to gcc's -gdwarf-5 > DW_AT_data_bit_offset, I think I should get that done and release 1.20, > if some bug is still left on that new code, we can just fallback to > -gdwarf-4. > > Then get back to the last 2 patches in your series, ok? > That's fine. I've spent a little time digging into what llvm-objcopy (11.0.0) is doing. It turns out it will rewrite an ELF file even if you just do llvm-objcopy --dump-section .strtab=/dev/null elf_file, and even if the file is not writable. Our AOSP kernels have a lot symbols filtered out of the symbol table and perhaps this is what makes such a difference to the size of .strtab after llvm-objcopy has done its thing. I will try on a vanilla kernel. Giuliano. > - Arnaldo > > > 3. Manually lay out updated ELF sections > > > > This does full layout of new and updated ELF sections. If the update > > ELF sections were not the last ones in the file by offset, then it can > > leave gaps between sections. > > > > 4. Align .BTF section to 8 bytes > > > > This was my original aim. > > > > Regards. > > > > Giuliano Procida (4): > > btf_encoder: Improve ELF error reporting > > btf_encoder: Add .BTF section using libelf > > btf_encoder: Manually lay out updated ELF sections > > btf_encoder: Align .BTF section to 8 bytes > > > > libbtf.c | 222 +++++++++++++++++++++++++++++++++++++++++++------------ > > 1 file changed, 175 insertions(+), 47 deletions(-) > > > > -- > > 2.30.0.280.ga3ce27912f-goog > > > > -- > > - Arnaldo
