RFR: 8336849: Remove .llvm_addrsig section from JDK/VM static libraries (.a files)

[Magnus Ihse Bursie]

On Sat, 20 Jul 2024 00:20:19 GMT, Jiangli Zhou <jiangli at openjdk.org> wrote:

> Please review this PR that strips the `.llvm_addrsig` section from JDK and hotspot `.a` static libraries when building with clang. Please see https://bugs.openjdk.org/browse/JDK-8336849 description for details.

But why and how do you specify `-Wl,--icf=safe` when building libjvm.a? That is not part of the linker flags in the JDK build mainline. I have not encountered these problems when trying to link with lld. 

Is it something you turn on explicitly in a separate branch? Or is it turned on by default by your lld version?

In any case, the links you provided explains why this approach is catastrophically wrong: 

> Other linkers, notably LLVM lld, supports --icf=safe. It uses .llvm_addrsig sections to identify functions that are safe to merge. Functions that are not mentioned in the section are not address-taken (no one takes its pointer), so they are safe to merge.

If you were to remove these sections, then the linker will believe that all functions are safe to merge. 

Yes, you will "solve" the problem with the error message, but the price you pay is that you get a binary that violates the C++ specification. 

If you really want that, then you should pass `--icf=all` to the linker, and then it will stop caring about  the `.llvm_addrsig` sections.

But from reading the links you sent, the safe and sound approach seems to be to send `--icf=none` to lld when it should operate on a partially linked (ld -r) .o file.

In any case, heavyhandedly cutting out sections like this seem utterly wrong.

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PR Comment: https://git.openjdk.org/jdk/pull/20265#issuecomment-2271291483