On Fri, Sep 15, 2017 at 10:33:09AM +0200, Michael Kerrisk (man-pages) wrote:
> Hi Yubin,
>
> On 15 September 2017 at 10:44, Yubin Ruan <ablacktshirt@xxxxxxxxx> wrote:
> > i,
> > I need some clarification on dl_iterate_phdr(3):
> >
> > it is claimed that the returned "struct dl_phdr_info" argument has the
> > following structure:
> >
> > struct dl_phdr_info {
> > ElfW(Addr) dlpi_addr; /* Base address of object */
> > const char *dlpi_name; /* (Null-terminated) name of
> > object */
> > const ElfW(Phdr) *dlpi_phdr; /* Pointer to array of
> > ELF program headers
> > for this object */
> > ElfW(Half) dlpi_phnum; /* # of items in dlpi_phdr */
> >
> > /* The following fields were added in glibc 2.4, after the first
> > version of this structure was available. Check the size
> > argument passed to the dl_iterate_phdr callback to determine
> > whether or not each later member is available. */
> >
> > unsigned long long int dlpi_adds;
> > /* Incremented when a new object may
> > have been added */
> > unsigned long long int dlpi_subs;
> > /* Incremented when an object may
> > have been removed */
> > size_t dlpi_tls_modid;
> > /* If there is a PT_TLS segment, its module
> > ID as used in TLS relocations, else zero */
> > void *dlpi_tls_data;
> > /* The address of the calling thread's instance
> > of this module's PT_TLS segment, if it has
> > one and it has been allocated in the calling
> > thread, otherwise a null pointer */
> > };
> >
> > and:
> >
> > The dlpi_addr field indicates the base address of the shared object
> > (i.e., the difference between the virtual memory address of the
> > shared object and the offset of that object in the file from which it
> > was loaded). The dlpi_name field is a null-terminated string giving
> > the pathname from which the shared object was loaded.
> >
> > What does it mean by "the offset of that object in the file from which it was
> > loaded"??? For a shared object, can I assume that this value is always 0? And
> > in what circumstance will it not be 0?
> >
> > The same statement has also been seen at the old man page[1], so I guess the
> > author
>
> (That would be me.)
>
> > might have done some copy&paste and overlook this detail.
>
> Can I suggest that as a first step to investigating that you modify
> the example program in thepage to print out the values of these
> fields?
Hmm..based on my understanding of the ELF format and linker/loader, that
`p_vaddr' should be 0 for a executable, and should be the runtime address for a
share object. But I have to take some time and look into the source first. If
that is indeed the case, I would suggest some modification to this man page...
Yubin
--
To unsubscribe from this list: send the line "unsubscribe linux-man" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
