Re: dl_iterate_phdr() behaves differently on musl and glibc

[Luc Van Oostenryck <luc.vanoostenryck@gmail.com>]

On Mon, May 28, 2018 at 04:02:43PM -0400, Rich Felker wrote:
> On Mon, May 28, 2018 at 03:44:15PM +0200, Bob B. wrote:
> > Hi list.
> > 
> > I noticed a difference in behavior of dl_iterate_phdr() when playing with musl and glibc.
> > The program I tried was the example on the bottom of the page: https://linux.die.net/man/3/dl_iterate_phdr
> > 
> > What happens is that musl returns the program itself when run + shared objects.
> > glibc only returns the shared objects.
> > 
> > Not sure which one is right. Or if both are acceptable.
> > Any light to clear why the different behavior is appreciated.
>
> I was unaware of that difference, but omitting the main program seems
> like a serious limitation that makes the interface a lot less useful.
> I'm not sure if there's any other way to get the information.
> 
> The manual page documents the function as enumerating the "shared
> objects", which one could interpret only as libraries, but I usually
> consider a dynamic program as a "shared object" itself.
> 

On a recent Ubuntu, the example in the manpage clearly shows that
the entry for the program itself is also present. And I confirm
it effective does:
	Name: "" (9 segments)
	     0: [0x5582f02f5040; memsz:    1f8] flags: 0x4; PT_PHDR
	     1: [0x5582f02f5238; memsz:     1c] flags: 0x4; PT_INTERP
	     2: [0x5582f02f5000; memsz:    bf8] flags: 0x5; PT_LOAD
	     3: [0x5582f04f5da0; memsz:    278] flags: 0x6; PT_LOAD
	     4: [0x5582f04f5db0; memsz:    1f0] flags: 0x6; PT_DYNAMIC
	     5: [0x5582f02f5254; memsz:     44] flags: 0x4; PT_NOTE
	     6: [0x5582f02f5a8c; memsz:     44] flags: 0x4; PT_GNU_EH_FRAME
	     7: [0x5582f02f5000; memsz:      0] flags: 0x6; PT_GNU_STACK
	     8: [0x5582f04f5da0; memsz:    260] flags: 0x4; PT_GNU_RELRO
	Name: "linux-vdso.so.1" (4 segments)
	     0: [0x7ffc899fe000; memsz:   100b] flags: 0x5; PT_LOAD
	     1: [0x7ffc899fe348; memsz:    120] flags: 0x4; PT_DYNAMIC
	     2: [0x7ffc899fe7a8; memsz:     3c] flags: 0x4; PT_NOTE
	     3: [0x7ffc899fe7e4; memsz:     3c] flags: 0x4; PT_GNU_EH_FRAME
	Name: "/lib/x86_64-linux-gnu/libc.so.6" (10 segments)
	     0: [0x7f552960a040; memsz:    230] flags: 0x4; PT_PHDR
	     1: [0x7f55297c7d50; memsz:     1c] flags: 0x4; PT_INTERP
	     2: [0x7f552960a000; memsz: 1e6aa0] flags: 0x5; PT_LOAD
	     3: [0x7f55299f1620; memsz:   94c0] flags: 0x6; PT_LOAD
	     4: [0x7f55299f4b80; memsz:    1e0] flags: 0x6; PT_DYNAMIC
	     5: [0x7f552960a270; memsz:     44] flags: 0x4; PT_NOTE
	     6: [0x7f55299f1620; memsz:     90] flags: 0x4; PT_TLS
	     7: [0x7f55297c7d6c; memsz:   59dc] flags: 0x4; PT_GNU_EH_FRAME
	     8: [0x7f552960a000; memsz:      0] flags: 0x6; PT_GNU_STACK
	     9: [0x7f55299f1620; memsz:   39e0] flags: 0x4; PT_GNU_RELRO
	Name: "/lib64/ld-linux-x86-64.so.2" (7 segments)
	     0: [0x7f55299fb000; memsz:  26c24] flags: 0x5; PT_LOAD
	     1: [0x7f5529c22680; memsz:   1af0] flags: 0x6; PT_LOAD
	     2: [0x7f5529c22e68; memsz:    170] flags: 0x6; PT_DYNAMIC
	     3: [0x7f55299fb1c8; memsz:     24] flags: 0x4; PT_NOTE
	     4: [0x7f5529a1f144; memsz:    66c] flags: 0x4; PT_GNU_EH_FRAME
	     5: [0x7f55299fb000; memsz:      0] flags: 0x6; PT_GNU_STACK
	     6: [0x7f5529c22680; memsz:    980] flags: 0x4; PT_GNU_RELRO

The same manpage can be found at:
	http://man7.org/linux/man-pages/man3/dl_iterate_phdr.3.html

-- Luc