Hi. On Thu, 4 Feb 2021 at 04:13, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Mon, Feb 1, 2021 at 9:26 AM Giuliano Procida <gprocida@xxxxxxxxxx> wrote: > > > > pahole -J needs to do the following to an ELF file: > > > > * add or update the ".BTF" section > > * maybe update the section name string table > > * update the Section Header Table (SHT) > > > > libelf either takes full control of layout or requires the user to > > specify offset, size and alignment of all new and updated sections and > > headers. > > > > To avoid libelf moving program segments in particular, we position the > > It's not clear to me what's wrong with libelf handling all the layout. > Even if libelf will move program segments around, what's the harm? > Does it break anything if we just let libelf do this? > It doesn't hurt the userspace case I care about. I've no idea what it means in terms of vmlinux. However, I wrote that text before I discovered that pahole -J isn't actually used to modify kernel images. One thing I haven't tried is to try to make .BTF loadable but leave placement to libelf. > > ".BTF" and section name string table (typically named ".shstrtab") > > sections after all others. The SHT always lives at the end of the file. > > > > Note that the last section in an ELF file is normally the section name > > string table and any ".BTF" section will normally be second last. > > However, if these sections appear earlier, then we'll waste some space > > in the ELF file when we rewrite them. > > > > Signed-off-by: Giuliano Procida <gprocida@xxxxxxxxxx> > > --- > > libbtf.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-- > > 1 file changed, 62 insertions(+), 2 deletions(-) > > > > [...]
