Re: musl built with pcc yields segfaults in dynlink.c

[Rich Felker <dalias@libc.org>]

On Tue, Jan 06, 2015 at 02:56:50PM -0800, Isaac Dunham wrote:
> On Tue, Jan 06, 2015 at 03:49:24PM -0500, Rich Felker wrote:
> > On Mon, Jan 05, 2015 at 11:48:50PM -0800, Isaac Dunham wrote:
> > > Hello,
> > > I'm trying to get a pcc-built libc.so that works.
> > > With the latest PCC, musl builds (lib/libc.so) and the result will display
> > > the proper messages if run from the command line without arguments.
> > > However, if I try to run a program with it 
> > > (even via -Wl,-dynamic-linker,`pwd`/lib/libc.so), I get a segfault
> > > in src/ldso/dynlink.c:
> > > (gdb) where
> > > #0  sysv_hash (s0=0x0, s0=0x0) at src/ldso/dynlink.c:177
> > > #1  0xb7f6f747 in find_sym (dso=0xbffffb18, rel=0xb7ffe1d4 <.L1502>, 
> > >     rel_size=<unknown type>, stride=<unknown type>, dso=0xbffffb18, 
> > >     rel=0xb7ffe1d4 <.L1502>, rel_size=<unknown type>, stride=<unknown type>)
> > >     at src/ldso/dynlink.c:251
> > >     #2  0xb7f6f916 in do_relocs () at src/ldso/dynlink.c:308
> > >     Backtrace stopped: frame did not save the PC
> > > 
> > > I'm using Alpine Linux edge, recently updated, with linux-vanilla.
> > 
> > It would be helpful to see the readelf -a output for libc.so and the
> > binary using it, and whatever information gdb can give on the value of
> > local vars at each of the above call frames.
> 
> Attaching a tar.xz containing the output of:
> - readelf -a lib/libc.so:	libc-pcc.readelf
> - readelf -a a.out:		argvname.readelf
> - echo -e 'run\nwhere\nbt full' |gdb ./a.out:	argvname.gdb
>  (which is substantially similar to the output for "lib/libc.so ./a.out")
> - and the source for a.out:	argvname.c
> 
> It's 51k, so I'm hoping it gets through.

It came through fine, but I suspect the debug info is bogus. The
values being shown don't seem to make sense. It might help more to
show the disassembly at eip and the value of all registers, or to post
the binaries somewhere I could download and analyze them. I looked at
the readelf outputs and didn't see any invalid relocs immediately, so
I'm not sure what's happening.

Rich