Opened 5 months ago

Last modified 3 months ago

#14531 new bug

dlopen: program symbols override the one used by library

Reported by: leorize Owned by: nobody
Priority: high Milestone: Unscheduled
Component: System/runtime_loader Version: R1/Development
Keywords: Cc:
Blocked By: Blocking:
Has a Patch: no Platform: All


The snippet attached below describe this problem.

How to run:

$ gcc -o dl dl.c
$ gcc -DLIBRARY -shared -o dl.c


from library


from program

The snippet has been tested on Linux, OpenBSD, FreeBSD and so far only Haiku exhibit this behavior.

Attachments (1)

dl.c (504 bytes) - added by leorize 5 months ago.

Download all attachments as: .zip

Change History (8)

Changed 5 months ago by leorize

Attachment: dl.c added

comment:1 Changed 4 months ago by leorize

As a walkaround, the binary can be compiled with -fvisibility=hidden to get the desired behavior

comment:2 Changed 4 months ago by leorize

It's found that if the binary was compiled with -pie, we can get the desired behavior.

comment:3 Changed 4 months ago by korli

Priority: highnormal

comment:4 Changed 3 months ago by waddlesplash

Component: System/POSIXSystem/runtime_loader
Priority: normalhigh

You don't even need dlopen, this will happen with just regular shared libraries; and the symbols can even be "semi-hidden" as they are when a static library is linked into a regular library.

So this is a higher-priority issue, then.

comment:5 Changed 3 months ago by jackburton

Does this happen also on x64 or only or x86/gcc2 ?

comment:6 Changed 3 months ago by waddlesplash

Actually it happens on GCC7 only, GCC2 is unaffected. Further testing finds that this affects regular library loads, not just dlopen ones. E.g. a library can have a local function called calloc and then it will override the one from libroot. I'll attach a test binary later.

Adding -Xlinker -Bsymbolic to GCC7 linkspec fixes the issue. Why aren't we doing that already?

comment:7 Changed 3 months ago by leorize

It's a separate issue. Using -Bsymbolic does not solve the problem for dlopen(), only for linked libraries.

The linkspec of gcc2 is vastly different from gcc7, and I still haven't know why. I'll push a PR to adjust gcc7 linkspec later.

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