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Re: Register a signal handler in _dl_start to handle SIGSEGV for dynamic linker
- From: "Carlos O'Donell" <carlos at systemhalted dot org>
- To: wuxi <wu dot andrew dot xi at gmail dot com>
- Cc: glibc-help <libc-help at sourceware dot org>
- Date: Tue, 2 Sep 2008 08:08:11 -0400
- Subject: Re: Register a signal handler in _dl_start to handle SIGSEGV for dynamic linker
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- References: <48BC85CA.firstname.lastname@example.org>
On Mon, Sep 1, 2008 at 8:16 PM, wuxi <email@example.com> wrote:
> My problem is, when I hook signal handler at _dl_start (very start of the
> dynamic linker, according to my study of code) to enable taint tracking for
> dynamic linker, the special signal handler seems not work - that is, when I
> run ld.so, it reports Segment fault directly without trapping into my own
> signal handler. However, I dump the code and discover the hook function has
> been called before such access.
When asking a complex question please *also* post your patch to the
code. This allows the reviewer to read the patch, read your question,
and see if anything is missing.
> So, am I missing something here to register a signal handler for dynamic
Yes. You should not be making function calls into libc *before* the
dynamic loader has relocated itself.
You must only install a signal handler after
elf/rtld.c (_dl_start) line 539 in libc cvs head
e.g. bootstrap_map.l_relocated = 1;
Before this line it is not safe to make function calls into libc.