On Tue, Jun 16, 2020 at 11:12:53AM +0200, Peter Zijlstra wrote:
> On Fri, Jun 12, 2020 at 04:30:36PM +0200, Peter Zijlstra wrote:
> > +int elf_write_insn(struct elf *elf, struct section *sec,
> > + unsigned long offset, unsigned int len,
> > + const char *insn)
> > +{
> > + Elf_Data *data = sec->data;
> > +
> > + if (data->d_type != ELF_T_BYTE || data->d_off) {
> > + WARN("write to unexpected data for section: %s", sec->name);
> > + return -1;
> > + }
> > +
> > + memcpy(data->d_buf + offset, insn, len);
> > + elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
> > +
> > + sec->changed = true;
> > + elf->changed = true;
> > +
> > + return 0;
> > +}
> > +
> > +int elf_write_reloc(struct elf *elf, struct reloc *reloc)
> > +{
> > + struct section *sec = reloc->sec;
> > +
> > + if (sec->sh.sh_type == SHT_REL) {
> > + reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
> > + reloc->rel.r_offset = reloc->offset;
> > +
> > + if (!gelf_update_rel(sec->data, reloc->idx, &reloc->rel)) {
> > + WARN_ELF("gelf_update_rel");
> > + return -1;
> > + }
> > + } else {
> > + reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
> > + reloc->rela.r_addend = reloc->addend;
> > + reloc->rela.r_offset = reloc->offset;
> > +
> > + if (!gelf_update_rela(sec->data, reloc->idx, &reloc->rela)) {
> > + WARN_ELF("gelf_update_rela");
> > + return -1;
> > + }
> > + }
> > +
> > + sec->changed = true;
> > + elf->changed = true;
> > +
> > + return 0;
> > +}
>
> Doing the change Matt asked for #1, I realized that sec->changed is only
> required if we need to rewrite the section header, neither of these two
> changes requires that, they already mark the elf data dirty so
> elf_update() DTRT.
This is really useful information.
As long as you're adding the elf->changed flag it might make sense to add this
as a comment in the struct section definition or even rename sec->changed
to reflect this (e.g. sec->shdr_changed).
Cheers,
-Matt Helsley
