Re: [Elftoolchain-developers] [patch] experiment of porting libelf to Debian

[Joseph K. <jk...@us...>]

> I've been trying to port libelf to Debian today, and I managed
> make it basically working. There are some issues unclear to me:

Thanks.  Giridhar (yganag@) had sent in a patch for a prior revision
of libelf, enabling compilation for GNU/Linux, GNU/Hurd, and
GNU/kFreeBSD.

I'll take a stab at merging the information in both patches.

kaiw> I found that there are two versions of ELF header files which
kaiw> contain ELF structures and other definitions. One is provided by
kaiw> GNU libc, the other one is linux/elf.h(includes asm/elf.h, etc,
kaiw> provided by kernel? ).  I noticed that the one provided by GNU
kaiw> libc has more definitions thus maybe better for us to use. But
kaiw> asm/elf.h provides arch-dependent defines.

kaiw> So, in the patch I included asm/elf.h in _libelf_config.h to get
kaiw> arch-dependent defines (ELF_CLASS, ELF_ARCH, ELF_DATA), and
kaiw> included elf.h(GNU libc) in libelf.h.

This seems ok.

kaiw> 2. strlcat/strlcpy

kaiw> These two functions are very convenient but unfortunately not inside
kaiw> GNU libc. I guess there are two solutions for this:

kaiw> a) Use portable strncpy/strncat, as a result, the code will become
kaiw>    less elegant.
kaiw> b) define strlcpy/strlcat.

kaiw> In the patch I chose b), I added a file called libelf_util.c which
kaiw> defines these two function. (stolen from FreeBSD libc)

yganag> For Debian, these definitions are provided in the libbsd
yganag> package.  For other Linuxes, we would have to define these.

The strl*() APIs are cleaner, but I'm wondering if we should just bite
the bullet and stick to the portable APIs.

For example:

Index: elf_errmsg.c
===================================================================
--- elf_errmsg.c	(revision 209)
+++ elf_errmsg.c	(working copy)
@@ -27,6 +27,7 @@
 #include <sys/cdefs.h>
 
 #include <libelf.h>
+#include <stdio.h>
 #include <string.h>
 
 #include "_libelf.h"
@@ -74,11 +75,9 @@
 	if (error < 0 || error >= ELF_E_NUM)
 		return _libelf_errors[ELF_E_NUM];
 	if (oserr) {
-		strlcpy(LIBELF_PRIVATE(msg), _libelf_errors[error],
-		    sizeof(LIBELF_PRIVATE(msg)));
-		strlcat(LIBELF_PRIVATE(msg), ": ", sizeof(LIBELF_PRIVATE(msg)));
-		strlcat(LIBELF_PRIVATE(msg), strerror(oserr),
-		    sizeof(LIBELF_PRIVATE(msg)));
+		(void) snprintf(LIBELF_PRIVATE(msg),
+		    sizeof(LIBELF_PRIVATE(msg)), "%s: %s",
+		    _libelf_errors[error], strerror(oserr));
 		return (const char *)&LIBELF_PRIVATE(msg);
 	}
 	return _libelf_errors[error];


Comments?

kaiw> 3. STAILQ Should we just add missing STAILQ defines like we did
kaiw> for NetBSD?

Question 1: Is there a package that provides <sys/queue.h> for
GNU/Linux?

Question 2: is there a way to distinguish between Debian GNU/Linux and
the other distributions at compile time?  E.g., is a __Debian__ or
other pre-processor symbol defined at compile time?

kaiw> 4. pmake compatibility

kaiw> a) Seems that header files (gelf.h, libelf.h) can not be
kaiw> installed.  After I typed "pmake install", libraries and manual
kaiw> pages got installed, but not header files.

If there's a port of NetBSD `bmake', could you try that instead of
pmake?

    http://www.crufty.net/help/sjg/bmake.html

kaiw> b) GNU and BSD tsort are probably incompatibible, you can see some
kaiw> tsort warnings during compiling, but I don't know if that affects the
kaiw> resulting files.

What are these warnings?  Our Makefiles don't invoke tsort directly
so if there are warnings we would need to look at the packaged
<bsd.lib.mk>.

Koshy