RFR: 8331541: [i386] linking with libjvm.so fails after JDK-8283326

[Magnus Ihse Bursie]

On Thu, 2 May 2024 08:23:38 GMT, Vladimir Petko <vpetko at openjdk.org> wrote:

> Hi, 
> 
> The     `.type _SafeFetch32_impl, at function` symbol declaration contains a spurious underscore causing an undefined symbol in libjvm.so.
> 
> I am not sure about change in default flags. I have removed the flag that allows linking with undefined symbols
> because having the flag on might cause bugs like this one or https://bugs.openjdk.org/browse/JDK-8329983 as the build succeeds even if some symbols are not defined.
> Openjdk builds successfully without it on amd64, i386, armhf, arm64, s390, ppc64el and riscv64 with this change[1]. riscv64 build was done locally inside vm:
> 
> Finished building target 'images' in configuration 'linux-riscv64-server-release'
> ubuntu at ubuntu:~/jdk$ 
> 
> Unfortunately I do not know why it was introduced, so I might be missing something.
> I am happy to drop it from this one or move it to a separate issue/pr.
>  
> [1] https://launchpad.net/~vpa1977/+archive/ubuntu/october-21/+sourcepub/16076564/+listing-archive-extra

So, after sleeping on this, here is my analysis/verdict:
1) The fix on renaming the `.type` directive looks good. This is the actual bug fix.

2) We can remove `--allow-shlib-undefined`. That just overrides `--no-allow-shlib-
undefined`, which has been the default for years and years, and there is no good reason to have it. It is not strictly related to the bug fix per se, but we can do that in this PR as well to keep things simpler.

3) The reason this could happen was since we used assembler code. A similar problem in C++ code would not have been allowed by the compiler.

4) If we introduce a common macro as I suggest, we can avoid this ever happening again. So while the linker cannot guarantee the consistency when linking libjvm.so (which I really would have liked), by using a stricter scheme when defining symbols in assembly code, we can make sure to avoid it.

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Marked as reviewed by ihse (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/19048#pullrequestreview-2045354117