Fix order of singlefilehost libarires passed to the linker #42094
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We give a list of arguments to the linker which includes a list of
static objects we want to be linked together and a set of system-wide
native libraries they should be dynamically linked against.
Some build environments, such as Fedora, use the `--as-needed` linker
flag. This makes the linker pay attention to the order in which
libraries appear and remove uneeded libararies.
When the linker sees this:
ld --as-needed -lz staticobject.a
It works from left to right and sess that nothing so far depends on
libz. The linker removes libz from the set of objects being linked. Then
it links staticobject.a, which needs symbols from libz. The linker then
complains that it contains an undefined reference.
We can fix that by changing the order so that dependencies appear last
in the linker command line:
ld --as-needed staticobject.a -lz
This makes the linker link staticobject.a against libz correctly.
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I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label. |
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I found this bug when trying to build .NET 5.0 Preview 8 (using source-build) on Fedora 32. cc @dleeapho |
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@janvorli Can you help me find some reviewers? I have a fix for #41768 (see dotnet/source-build#1755) that touches these lines too and I want to get this merged before doing a PR for that. |
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@omajid I'll review it. I am sorry for missing this PR before. |
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Thanks! |
This was referenced Sep 24, 2020
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We give a list of arguments to the linker which includes a list of static objects we want to be linked together and a set of system-wide native libraries they should be dynamically linked against.
Some build environments, such as Fedora, use the
--as-neededlinker flag. This makes the linker pay attention to the order in which libraries appear and remove uneeded libararies.When the linker sees this:
It works from left to right and sees that nothing so far depends on libz. The linker removes libz from the set of objects being linked. Then it links staticobject.a, which needs symbols from libz. The linker then complains that it contains an undefined reference.
We can fix that by changing the order so that dependencies appear last in the linker command line:
This makes the linker link staticobject.a against libz correctly.