[Bug dynamic-link/29567] New: when `dlopen` glibc itself, it needs `__ctype_init`

[Bug dynamic-link/29567] New: when `dlopen` glibc itself, it needs `__ctype_init`

[linjy0410 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29567

            Bug ID: 29567
           Summary: when `dlopen` glibc itself, it needs `__ctype_init`
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: linjy0410 at gmail dot com
  Target Milestone: ---

We met an issue that while `dlopen("libc.so.6")` and using dlsym to call the
functions inside, some will crash because of ctype TLS is not initialized, e.g.
`iconv` that uses `isspace` which would access ctype.
By manual dlsym and calling `__ctype_init`, it can work normally.
I'm not sure whether this is a bug or dlopen a glibc is not intended.

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[Bug dynamic-link/29567] when `dlopen` glibc itself, it needs `__ctype_init`

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29567

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-09-13
                 CC|                            |fweimer at redhat dot com
             Status|UNCONFIRMED                 |WAITING
     Ever confirmed|0                           |1

--- Comment #1 from Florian Weimer <fweimer at redhat dot com> ---
Could you share a reproducer, please? Does it involve static dlopen? Thanks.

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[Bug dynamic-link/29567] when `dlopen` glibc itself, it needs `__ctype_init`

[linjy0410 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29567

--- Comment #2 from jy l <linjy0410 at gmail dot com> ---
Created attachment 14334
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14334&action=edit
iconv_open segfault poc

I pull the latest glibc and build/install it to `glibcinstallamd64`, with gcc
9.4.0.
And compile this poc by `gcc poc.c -ldl` with my system libc which is 2.31.
It segfault on my machine when calling the `func` (iconv_open), didn't have any
static dlopen I think.

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[Bug dynamic-link/29567] when `dlopen` glibc itself, it needs `__ctype_init`

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29567

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |INVALID

--- Comment #3 from Florian Weimer <fweimer at redhat dot com> ---
I'm afraid this is expected: the dynamic loader from the system libc is not
able to load libc.so.6 from the version you just built. Dynamic loader and
libc.so.6 must come from the exact same build.

You need to run your application with the new dynamic loader, too. Use an
explicit ld.so invocation (see the testrun.sh in the build tree for an
example), or set the loader with the -Wl,--dynamic-linker= option. You may also
have to link to the new glibc startup files,
<https://sourceware.org/glibc/wiki/Testing/Builds#Build100PctNew> has the
details.

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