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Re: Documenting the (dynamic) linking rules for symbol versioning


On 04/20/2017 02:58 PM, Siddhesh Poyarekar wrote:
On Thursday 20 April 2017 06:10 PM, Michael Kerrisk (man-pages) wrote:
I think that I have failed to provide enough detail for
you to understand what I meant. Consider the following:

1. We want to interpose some symbol in glibc (say, "malloc@GLIBC_2.0")
    with a symbol of our own (perhaps via a preloaded library).
2. In our preloaded shared library, the interposing "malloc"
    need not be a versioned symbol.

At least

Ah ok, got it.  The dlsym will result in picking up the latest symbol.

Note the last line: dlsym() found xyz@@VER_2 (not xyz@VER_3).

Hmm interesting, I thought 'latest' would imply the last version in the
sequence of versions in the map, but I guess it kinda makes sense that
it is the @@ default, similar to how a static linker would pick it up.

It might be another instance of bug 12977. At least its fix will involve preferring the default version in this case. I don't know what to do if there is no default version. We currently do not perform a topological sort on the version graph to find the maximum version.

Florian


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