Re: dynamic linker command line invocation

[Rich Felker <dalias@libc.org>]

On Tue, Jan 05, 2016 at 01:00:37PM -0500, N Jain wrote:
> > You never answered whether
> > you were setting up the aux vector right, but if not, that's
> > definitely going to cause problems.
> 
> I am not setting any aux vectors. I only pass argv = "app.elf" and argc = 1
> to dynamic linker.
> What and where I need to set "aux" vectors ? Any pointers will help..

The ELF entry point ABI is that the initial stack pointer points to an
array of word-sized cells containing:

argc argv[0] argv[1] ... argv[argc-1] argv[argc](=0) anviron[0]
environ[1] ... 0 auxv[0].key auxv[0].val auxv[1].key auxv[1].val ... 0

The auxv items are key,val pairs where the key is one of the AT_*
constants from elf.h and the value is either an integer or pointer
(depending on which key it's for). At the very least you should be
passing:

AT_PHDR - points to the start of elf program headers
AT_PHENT - size of each program header
AT_PHNUM - number of program headers

If you load both the main program and "interpreter" (dynamic linker)
from the kernel, then these values should be for the main program's
headers, and in addition you need to pass:

AT_BASE - load address of the "interpreter" (dynamic linker)
AT_ENTRY - entry point address of the main program, from its header

On the other hand, if you only load the dynamic linker (treating it as
the main program), then the program header auxv entries should hold
the right values for the dynamic linker.

Rich