Only strip the producers' section in optimized builds #11996
Conversation
| # the specific difference is that LLVM emits language info (C_plus_plus_14) | ||
| # when emitting debug info, but not otherwise. | ||
| self.assertLess(no_size, line_size) | ||
| self.assertEqual(line_size, full_size) |
There was a problem hiding this comment.
Do we need this change, given that we already test this specifically below?
I find this test already to be a little to long/complex for a unittest.
There was a problem hiding this comment.
This test is important in general for checking what happens with debug info when compiling to object files first and then linking them. That is not checked by the main test for the producer's section that you mentioned lower down (it compiles straight to an executable, and it doesn't look at debug info). I think it's worth adding this as I found a curious interaction between the two (mentioned in the comment here) which confused me when working on this. The test addition here both explains that, and will prevent accidentally breaking anything with the producers' section / debugging interaction as we make changes on both sides.
ChangeLog.md
Outdated
| in release builds, which is not changing here; if you want to not have a | ||
| producer's section in debug builds, you can either tell LLVM to not emit it in | ||
| the first place, or you can run `wasm-opt --strip-producers` (which is what | ||
| Emscripten does in release builds). |
There was a problem hiding this comment.
I don’t remember having an LLVM option to skip the producer’s section. I think it may be unconditional. It would be simple to add an LLVM option for this if you think it is important.
There was a problem hiding this comment.
Maybe we don't need an LLVM option, if it hasn't come up yet. We can wait to see if people ask for it I guess.
…opt (#12075) As part of WebAssembly/binaryen#3043 we stopped stripping the producers section in unoptimized builds in #11996 However there is a way to still strip it with very little overhead, using llvm-objcpy. This PR makes us strip it using wasm-opt normally if we are running wasm-opt anyhow, but if we are not (as we hope to get to soon in some builds) then it uses llvm-objcpy. This does a little more work after link but it's pretty trivial and does not rewrite code or anything like that. This does add some complexity, but it is complexity we'll need anyhow for not running wasm-opt when it isn't needed. Fixes #12071
In
-O0builds we want to leave the wasm from LLVM unmodified as much aspossible (see WebAssembly/binaryen#3043), so this PR makes us stop modifying it to remove the
producers section.
There is no change to optimized builds (
-O1+), so release builds are not changed inany way.
There is also no change if the user told LLVM to not emit a producer's section
in the first place. We basically just do less things on
-O0builds after this PR,and leave it to LLVM.