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?
Thanks,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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