From: Ian Lance Taylor <iant@google.com>
To: John Marino <gnugcc@marino.st>
Cc: gcc-help <gcc-help@gcc.gnu.org>
Subject: Re: dl_iterate_phdr support
Date: Mon, 14 Feb 2011 08:11:00 -0000 [thread overview]
Message-ID: <mcrd3mvcibd.fsf@google.com> (raw)
In-Reply-To: <4D56F3A4.7010808@marino.st> (John Marino's message of "Sat, 12 Feb 2011 21:55:00 +0100")
John Marino <gnugcc@marino.st> writes:
> FreeBSD and openBSD have had dl_iterate_phdr support in their runtime
> linker since 2007. NetBSD-current added it in late 2010 and I just
> patched Dragonfly's RTLD to support it as well, which means the
> feature is fully supported by *BSD.
>
> I was a bit surprised when I checked the gcc configure log and saw the
> check for dl_iterate_phdr came back "unknown" so I checked the
> gcc/configure script.
>
> Basically the logic in the configure script is this:
> If target <> solaris2 then gcc_cv_target_dl_iterate_phdr=unknown
>
> Basically that means this feature is only possibly used by gcc when
> Solaris is the target.
>
> Is this intentional?
> Why are not Linux and BSD targets being tested?
>
> Is the problem only a deficient configure script, or is there missing
> support within gcc itself? I was told on the gcc-help mail list that
> using dl_iterate_phdr was a more efficient method of propagating
> exceptions and I'd like GNAT to take advantage of that.
The test in gcc/configure.ac is unfortunately rather misleading. That
result of that test is currently only used on Solaris.
The relevant code can be found in two places: gcc/unwind-dw2-fde-glibc.c
and gcc/crtstuff.c. In unwind-dw2-fde-glibc.c it looks like this:
#if !defined(inhibit_libc) && defined(HAVE_LD_EH_FRAME_HDR) \
&& (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2) \
|| (__GLIBC__ == 2 && __GLIBC_MINOR__ == 2 && defined(DT_CONFIG)))
# define USE_PT_GNU_EH_FRAME
#endif
#if !defined(inhibit_libc) && defined(HAVE_LD_EH_FRAME_HDR) \
&& defined(__FreeBSD__) && __FreeBSD__ >= 7
# define ElfW __ElfN
# define USE_PT_GNU_EH_FRAME
#endif
#if !defined(inhibit_libc) && defined(HAVE_LD_EH_FRAME_HDR) \
&& defined(TARGET_DL_ITERATE_PHDR) \
&& defined(__sun__) && defined(__svr4__)
# define USE_PT_GNU_EH_FRAME
#endif
The idea is that USE_PT_GNU_EH_FRAME should be defined on any system for
which the linker supports --eh-frame-hdr and the library supports
dl_iterate_phdr. As you can see, the test is being done based on the
library version. It is done this way because when gcc is being used to
build the C library, particularly when building a cross-compiler, there
is no way to test the features that the C library supports.
Ian
next prev parent reply other threads:[~2011-02-14 5:10 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-13 2:15 John Marino
2011-02-14 8:11 ` Ian Lance Taylor [this message]
2011-02-14 15:48 ` John Marino
2011-02-14 17:46 ` Ian Lance Taylor
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