Re: [patch] Fix resolving ELF symbols for live PIDs with deleted files

[Mark Wielaard <mjw@redhat.com>]

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On Thu, 2014-08-28 at 22:12 +0200, Jan Kratochvil wrote:
> Formerly shared libraries did not get resolved properly:
> 	#2  0x00007fc4d86c56d6
> 	#3  0x0000000000400938 main
> 
> Fixed elfutils produce:
> 	#2  0x00007f61094876d6 libfunc
> 	#3  0x0000000000400938 main
> 
> Signed-off-by: Jan Kratochvil <jan.kratochvil@redhat.com>

Nice, thanks. I would add the why to the commit message. "For deleted
shared library files the offsets to the symbol table were calculated
wrongly from the phdrs because the main_bias wasn't taken into account."

+2014-08-28  Jan Kratochvil  <jan.kratochvil@redhat.com>
> +
> +	* dwfl_module_getdwarf.c (find_offsets): Add parameter main_bias, use
> +	it.
> +	(find_dynsym): Pass the new parameter main_bias.
> 
Looks good.

+# Older Linux (such as 2.6.32) required PTRACE_ATTACH to read /proc/PID/mem.
> +sleep 60 & p=$!; sleep 0.1
> +addr=0x$(cat /proc/$p/maps|sed -n 's#^\([0-9a-f]*\)-[0-9a-f]* r[^ ]* 00* .*/sleep$#\1#p'|head -n1)
> +supported=$[$(dd if=/proc/$p/mem bs=1 skip=$[$addr] count=1|wc -c)]
> +kill -9 $p
> +if [ $supported -eq 0 ]; then
> +  exit 77
> +fi
 
I don't think this check is needed. eu-stack needs to be attached to get
the register values and dwfl_linux_proc_find_elf makes sure the process
is attached before calling elf_from_remote_memory.

Cheers,

Mark