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Re: resolving kernel addresses to symbol names via /proc/kallsyms
- From: Mark Wielaard <mjw at redhat dot com>
- To: Milian Wolff <mail at milianw dot de>
- Cc: elfutils-devel at sourceware dot org
- Date: Wed, 01 Feb 2017 12:16:25 +0100
- Subject: Re: resolving kernel addresses to symbol names via /proc/kallsyms
- Authentication-results: sourceware.org; auth=none
- References: <3094525.5gWoQJ3HEP@milian-kdab2>
On Tue, 2017-01-31 at 14:39 +0100, Milian Wolff wrote:
> should I be able to resolve kernel addresses to symbol names with elfutils
Yes. See also eu-addr2line -k -S which I believe does what you are
trying to do below.
> I did something like this:
> m_dwfl = dwfl_begin(m_callbacks);
> auto i_k = dwfl_linux_kernel_report_kernel(m_dwfl);
> auto i_m = dwfl_linux_kernel_report_modules(m_dwfl);
> Both i_k and i_m returned 0. Then, I picked a random address from my /proc/
> kallsyms, e.g.:
> ffffffff81001000 T hypercall_page
> and try to find that symbol:
> auto module = dwfl_addrmodule(m_dwfl, 0xffffffff81001000ll);
> The module is non-null and points me at this module (comparing to output I get
> from dwfl_getmodules):
> 0x61400000fa40 kernel ffffffff81000000
You could also use dwfl_module_info () to get the name and other
information about the module found for that address.
> But when I try to get a symbol, I get a nullptr:
> auto sym = dwfl_module_addrname(module, 0xffffffff81001000ll);
> So, what am I missing?
I don't immediately know without seeing the full program.
You could try using dwfl_module_addrinfo () to see if you can get more
information about the address in that module.
You could also try calling dwfl_module_getsymtab () on the module and
look at some of the symbols found with dwfl_module_getsym_info () to see
if libdwfl found the symbol table for that module.
> Also, it doesn't seem to be possible to specify the path to the kallsyms file
> with the current dwfl_linux_kernel_report_kernel API - how is this intended to
> be handled? Should one instead use dwfl_linux_kernel_report_offline when one
> wants to support cross-machine analysis?
Yes, one should use dwfl_linux_kernel_report_offline when cross-machine
(or even just cross kernel version) analysis. The /proc/kallsyms file is
only used to estimate some running kernel address boundaries (but isn't