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Diffstat (limited to 'docs/users_guide/debug-info.rst')
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diff --git a/docs/users_guide/debug-info.rst b/docs/users_guide/debug-info.rst index e18f0287a4..ce640691a2 100644 --- a/docs/users_guide/debug-info.rst +++ b/docs/users_guide/debug-info.rst @@ -335,3 +335,61 @@ Further Reading For more information about the debug information produced by GHC see Peter Wortmann's PhD thesis, `*Profiling Optimized Haskell: Causal Analysis and Implementation* <http://etheses.whiterose.ac.uk/8321/>`__. + + +Direct Mapping +-------------- + +In addition to the DWARF debug information, which can be used by many +standard tools, there is also a GHC specific way to map info table pointers +to a source location. This lookup table is generated by using the ``-finfo-table-map`` flag. + + +.. ghc-flag:: -finfo-table-map + :shortdesc: Embed a lookup table in the generated binary which + maps the address of an info table to the source position + the closure originated from. + :type: dynamic + :category: debugging + + :since: 9.2 + + This flag enables the generation of a table which maps the address of + an info table to an approximate source position of where that + info table statically originated from. If you + also want more precise information about constructor info tables then you + should also use :ghc-flag:`-fdistinct-constructor-tables`. + + This flag will increase the binary size by quite a lot, depending on how + big your project is. For compiling a project the size of GHC the overhead was + about 200 megabytes. + +.. ghc-flag:: -fdistinct-constructor-tables + :shortdesc: Generate a fresh info table for each usage + of a data constructor. + :type: dynamic + :category: debugging + + :since: 9.2 + + For every usage of a data constructor in the source program + a new info table will be created. This is useful for debugging + as if each usage has a unique info table then the info table map + and profiling modes can distinguish the allocation sites of + a data constructor. + + + +Querying the Info Table Map +--------------------------- + +If it is generated then the info table map can be used +in two ways. + +1. The ``whereFrom`` function can be used to determine the source + position which we think a specific closure was created. +2. The complete mapping is also dumped into the eventlog. + +If you are using gdb then you can use the ``lookupIPE`` function +directly in order to find any information which is known +about the info table for a specific closure. |