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| author | Moritz Angermann <moritz@lichtzwerge.de> | 2014-11-19 16:38:22 -0600 |
|---|---|---|
| committer | Austin Seipp <austin@well-typed.com> | 2014-11-19 17:03:06 -0600 |
| commit | 53a4742d037da2bfd00d1d34a8ea0d49d4cdb490 (patch) | |
| tree | 1922721e21e3b6618ff9b7184d9dc96e9145e535 /compiler/NOTES | |
| parent | 146dd138e2c3b4ec9b211dcbcedf752aeb79d3d1 (diff) | |
| download | haskell-53a4742d037da2bfd00d1d34a8ea0d49d4cdb490.tar.gz | |
Allow -dead_strip linking on platforms with .subsections_via_symbols
Summary:
This allows to link objects produced with the llvm code generator to be linked with -dead_strip. This applies to at least the iOS cross compiler and OS X compiler.
Signed-off-by: Moritz Angermann <moritz@lichtzwerge.de>
Test Plan: Create a ffi library and link it with -dead_strip. If the resulting binary does not crash, the patch works as advertised.
Reviewers: rwbarton, simonmar, hvr, dterei, mzero, ezyang, austin
Reviewed By: dterei, ezyang, austin
Subscribers: thomie, mzero, simonmar, ezyang, carter
Differential Revision: https://phabricator.haskell.org/D206
Diffstat (limited to 'compiler/NOTES')
| -rw-r--r-- | compiler/NOTES | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/compiler/NOTES b/compiler/NOTES new file mode 100644 index 0000000000..14a1f80b41 --- /dev/null +++ b/compiler/NOTES @@ -0,0 +1,16 @@ +Note [Subsections Via Symbols] + +If we are using the .subsections_via_symbols directive +(available on recent versions of Darwin), +we have to make sure that there is some kind of reference +from the entry code to a label on the _top_ of of the info table, +so that the linker will not think it is unreferenced and dead-strip +it. That's why the label is called a DeadStripPreventer (_dsp). + +The LLVM code gen already creates `iTableSuf` symbols, where +the X86 would generate the DeadStripPreventer (_dsp) symbol. +Therefore all that is left for llvm code gen, is to ensure +that all the `iTableSuf` symbols are marked as used. +As of this writing the documentation regarding the +.subsections_via_symbols and -dead_stip can be found at +<https://developer.apple.com/library/mac/documentation/DeveloperTools/Reference/Assembler/040-Assembler_Directives/asm_directives.html#//apple_ref/doc/uid/TP30000823-TPXREF101>
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