[PATCH] D129107: [BOLT][HUGIFY] adds huge pages support of PIE/no-PIE binaries

[Rafael Auler via Phabricator via llvm-commits]

rafauler added a comment.

I tried to repro your test case and I can't actually get it to work, then I realized that the problem is the -fPIE flag to build hugify.cpp. This is also a good reason why we probably should put a special 'pie' test case here (a new line in user-func-reorder.c that also builds it with -pie). If we had that, we would more easily detect this problem earlier in the review.

Here's the problem. If you are going to build hugify.cpp with -fPIE, you have to use the same trick that @yota9 used here https://github.com/llvm/llvm-project/commit/af58da4ef3fbd766b2c44cfdbdb859a21022d10a (reviewed here https://github.com/facebookincubator/BOLT/pull/192).

When building a PIE object file, the compiler will address data objects through a GOT table, and our rudimentary linker that brings in hugify.o into the final binary is unable to properly handle GOT table creation. So, at least in my environment, when I try to run BOLT with hugify option using as input a PIE binary, I end up with hugify trying to copy the wrong start pointers because we failed to create runtime relocations to fix the addresses in the GOT table.

Hopefully by using the "#pragma GCC visibility push(hidden)" trick, you should easily fix this.


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https://reviews.llvm.org/D129107