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#[link_section] static FOO can contain undefined bytes on wasm #60633

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oli-obk opened this issue May 8, 2019 · 3 comments · Fixed by #62749
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#[link_section] static FOO can contain undefined bytes on wasm #60633

oli-obk opened this issue May 8, 2019 · 3 comments · Fixed by #62749
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A-const-eval Area: constant evaluation (mir interpretation) A-linkage Area: linking into static, shared libraries and binaries C-cleanup Category: PRs that clean code up or issues documenting cleanup. E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. O-wasm Target: WASM (WebAssembly), http://webassembly.org/

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@oli-obk
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oli-obk commented May 8, 2019 •
edited by rustbot
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https://github.com/rust-lang/rust/blob/e80c86c535b74cdd65c4b75b94ce38342d0bb946/src/librustc_typeck/check/mod.rs#L1444-L1467 only checks that the link section contains no pointers, but there may be arbitrary bytes in the data, even undefined bytes (e.g. due to padding).

cc @alexcrichton is that ok? llvm may insert undef whereever there are undefined bytes. Or should we lint/error on such statics?

This issue has been assigned to @Chocol4te via this comment.
@oli-obk oli-obk added A-const-eval Area: constant evaluation (mir interpretation) A-linkage Area: linking into static, shared libraries and binaries O-wasm Target: WASM (WebAssembly), http://webassembly.org/ labels May 8, 2019
@alexcrichton
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@oli-obk that should be ok yeah, I think that's what happens on all other platforms and it's up to the consumer to ensure that all bytes they read have defined values if they want.

@oli-obk oli-obk added C-cleanup Category: PRs that clean code up or issues documenting cleanup. E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. labels May 8, 2019
@oli-obk
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oli-obk commented May 8, 2019

Ok, I guess we should probably just document that in the code segment that I linked above.

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@rustbot claim

@rustbot rustbot self-assigned this Jul 17, 2019
@fmckeogh fmckeogh mentioned this issue Jul 17, 2019
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Mark-Simulacrum added a commit to Mark-Simulacrum/rust that referenced this issue Jul 18, 2019
@Mark-Simulacrum
Rollup merge of rust-lang#62749 - chocol4te:fix_60633, r=estebank
9c08b2b 
Document link_section arbitrary bytes

Closes rust-lang#60633.
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A-const-eval Area: constant evaluation (mir interpretation) A-linkage Area: linking into static, shared libraries and binaries C-cleanup Category: PRs that clean code up or issues documenting cleanup. E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. O-wasm Target: WASM (WebAssembly), http://webassembly.org/
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Document link_section arbitrary bytes
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@alexcrichton @oli-obk @fmckeogh @rustbot