[Bug dynamic-link/28453] New: ld.so segfaults when relocating x86 libstdc++.so compiled with -fno-plt

["alex_y_xu at yahoo dot ca" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=28453

            Bug ID: 28453
           Summary: ld.so segfaults when relocating x86 libstdc++.so
                    compiled with -fno-plt
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: alex_y_xu at yahoo dot ca
  Target Milestone: ---

Created attachment 13721
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13721&action=edit
x86 libstdc++.so.6.0.29 -fno-plt

after compiling gcc with -fno-plt, all c++ programs on x86 crash while
starting. I found that this is caused by SIGSEGV due to null dereference around
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/i386/dl-machine.h;hb=9d3c9a046a2d7cfc9cad18675612e5916c65d7d7#l78.
I can't recall 100% but I believe l->l_info[DT_PLTGOT] is NULL.

this can be reproduced by invoking ld-linux.so.2 on the attached file. invoking
it with LD_DEBUG=all results in printing "relocation processing:
./libstdc++.so.6.0.29 (lazy)", then segfaulting when accessing 0x4, whereas the
expected behavior would be printing "calling init: [library]" then segfaulting.

programs run successfully if LD_BIND_NOW=1 is set. normally, this issue should
not occur, since -fno-plt is usually paired with -Wl,-z,now. however, gcc
ignores LDFLAGS for this library, causing ld to default to lazy.

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