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| author | Ben Gamari <ben@smart-cactus.org> | 2019-12-27 12:38:27 -0500 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2020-11-11 03:20:00 -0500 |
| commit | c6264a2d652517954b7cd076c7bc4487ed17c97d (patch) | |
| tree | bd11c475186c63a147f5b58958458c9fc4eef68e /docs | |
| parent | 6e23695e7d84aa248e7ca20bdb8d133f9b356548 (diff) | |
| download | haskell-c6264a2d652517954b7cd076c7bc4487ed17c97d.tar.gz | |
codeGen: Produce local symbols for module-internal functions
It turns out that some important native debugging/profiling tools (e.g.
perf) rely only on symbol tables for function name resolution (as
opposed to using DWARF DIEs). However, previously GHC would emit
temporary symbols (e.g. `.La42b`) to identify module-internal
entities. Such symbols are dropped during linking and therefore not
visible to runtime tools (in addition to having rather un-helpful unique
names). For instance, `perf report` would often end up attributing all
cost to the libc `frame_dummy` symbol since Haskell code was no covered
by any proper symbol (see #17605).
We now rather follow the model of C compilers and emit
descriptively-named local symbols for module internal things. Since this
will increase object file size this behavior can be disabled with the
`-fno-expose-internal-symbols` flag.
With this `perf record` can finally be used against Haskell executables.
Even more, with `-g3` `perf annotate` provides inline source code.
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/phases.rst | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/docs/users_guide/phases.rst b/docs/users_guide/phases.rst index 1d22372889..88b6659a05 100644 --- a/docs/users_guide/phases.rst +++ b/docs/users_guide/phases.rst @@ -720,6 +720,19 @@ Options affecting code generation all target platforms. See the :ghc-flag:`--print-object-splitting-supported` flag to check whether your GHC supports object splitting. +.. ghc-flag:: -fexpose-internal-symbols + :shortdesc: Produce symbols for all functions, including internal functions. + :type: dynamic + :category: codegen + + Request that GHC emits verbose symbol tables which include local symbols + for module-internal functions. These can be useful for tools like + :ref:`perf <https://perf.wiki.kernel.org/>` but increase object file sizes. + + :ghc-flag:`-fno-expose-internal-symbols` suppresses all non-global symbol + table entries, resulting in smaller object file sizes at the expense of + debuggability. + .. _options-linker: Options affecting linking |