Re: [Libunwind-devel] [PATCH] Check that the CIE is within the segment

[Milian Wolff]

On Tuesday 25 November 2014 22:10:33 Peter Wu wrote:
> Due to a bug in the gold linker[1], the .eh_frame and .eh_frame_hdr
> sections contains garbage. When dwarf_extract_proc_info_from_fde tried
> to look up the begin of the CIE subsection, it would underflow the
> .eh_frame segment, resulting in a crash[2].
> 
> This patch avoids that crash by checking whether the CIE pointer is
> located after the begin of the .eh_frame section. The variable "base"
> was misused in various places as a boolean (decode as .debug_frame or
> decode as .eh_frame). These instances have been renamed to
> is_debug_frame where applicable.
> 
> Tested on Linux x86_64.
> 
>  [1]: https://sourceware.org/bugzilla/show_bug.cgi?id=17639
>  [2]:
> http://lists.nongnu.org/archive/html/libunwind-devel/2014-11/msg00009.html

Hello Peter,

I have an issue with your patch on my machine. With it applied, my tool fails 
to find backtraces. Attached, you find the libunwind debug output of current 
master with and without your patch applied. I've also modified libunwind to 
output a debug message when your patch hits, i.e. the cie_offset_addr < base 
conditional is met.

This apparently completely breaks libunwind on my machine...

3.17.6-1-ARCH
Intel(R) Core(TM)2 Quad CPU    Q9550  @ 2.83GHz
GNU gold (GNU Binutils 2.24) 1.11
gcc (GCC) 4.9.2

Do you need any other information?

Bye
-- 
Milian Wolff
address@hidden
http://milianw.de

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