On Sat, Jul 13, 2024 at 7:52 PM Max Filippov <jcmvb...@gmail.com> wrote:
>
> On Wed, Jul 10, 2024 at 12:49 PM Ian Lance Taylor <i...@google.com> wrote:
> > On Sun, May 26, 2024 at 11:51 PM Max Filippov <jcmvb...@gmail.com> wrote:
> > > diff --git a/libbacktrace/internal.h b/libbacktrace/internal.h
> > > index 4fa0af8cb6c9..456911166026 100644
> > > --- a/libbacktrace/internal.h
> > > +++ b/libbacktrace/internal.h
> > > @@ -323,10 +323,22 @@ struct dwarf_sections
> > >
> > > struct dwarf_data;
> > >
> > > +#if defined (HAVE_DL_ITERATE_PHDR) && defined (__FDPIC__)
> > > +typedef struct elf32_fdpic_loadaddr base_address_type;
> > > +#define __RELOC_UINTPTR(ptr, base) ((uintptr_t)__RELOC_POINTER (ptr,
> > > base))
> > > +#define no_base_address ((struct elf32_fdpic_loadaddr){0})
> > > +#else
> > > +typedef uintptr_t base_address_type;
> > > +#define __RELOC_POINTER(ptr, base) ((ptr) + (base))
> > > +#define __RELOC_UINTPTR(ptr, base) ((uintptr_t)__RELOC_POINTER (ptr,
> > > base))
> > > +#define no_base_address ((uintptr_t)0)
> > > +#endif
> > > +
> > > +
> >
> > When I look at the uClibc sources, I don't understand how this works.
> > This sets no_base_address to have a zero map field. But
> > __RELOC_POINTER will crash when given a zero map field.
>
> That's right. But __RELOC_POINTER should never be called for base
> address set to no_base_address, that's what the following hunk ensures:
>
> --->8---
> @@ -6636,9 +6636,15 @@ elf_add (struct backtrace_state *state, const
> char *filename, int descriptor,
>
> /* If the executable is ET_DYN, it is either a PIE, or we are running
> directly a shared library with .interp. We need to wait for
> - dl_iterate_phdr in that case to determine the actual base_address. */
> + dl_iterate_phdr in that case to determine the actual base_address.
> + In case of FDPIC we always need the actual base_address. */
> +#ifndef __FDPIC__
> if (exe && ehdr.e_type == ET_DYN)
> return -1;
> +#else
> + if (exe)
> + return -1;
> +#endif
>
> shoff = ehdr.e_shoff;
> shnum = ehdr.e_shnum;
I see. The code is using dl_iterate_phdr for everything. This is a
confusing execution flow. It means that we do some pointless work.
Ian
