Create inlinedFunctions.md -- high-ish level write up on how we curre…

…ntly find inlined functions

doc/inlinedFunctions.md

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+# Inlined Function Identification
+
+This file describes the process of identifying functions that have been inlined by the Go compiler. 
+It also details how this process is implemented in GoReSym and lists known TODOs.
+
+## Finding []runtime__inlinedCall
+
+These steps calculate where to find the inline tree for a function `f` . 
+The inline tree holds information about any and all functions that were inlined into `f` by the Go compiler.
+The documentation implies that each function that contains inlined functions will have its own distinct tree.
+
+1. Choose a function `f`
+2. Get `funcData` for `f`.
+3. Check whether `funcData.funcdata[FUNCDATA_InlTree]` exists (want `funcData.nfuncdata` >= `FUNCDATA_InlTree`)
+4. Check whether `funcData.funcdata[FUNCDATA_InlTree]` is valid (want `funcData.funcdata[FUNCDATA_InlTree]` != `^uint32(0)`)
+5. Save `funcData.funcdata[FUNCDATA_InlTree]` -- this is the inline tree offset for `f`
+6. Get `go:func.*` via `moduledata`. (there are other ways but this is the least complicated)
+7. Adjust `go:func.*` from absolute address to file offset by subtracting the preferred base address (in file header). `go:func.* -= baseAddress`
+9. Go to inline tree. InlineTreeAddress = `go:func.*` + `funcData.funcdata[FUNCDATA_InlTree]`.
+
+   *NOTE: the inline tree and `go:func.*` addresses may be earlier in the binary than `pclntab`*
+   Therefore whatever component resolves inline functions MUST have access to the full file.
+
+## Resolving a single runtime__inlinedCall
+
+
+
+## Known issues
+
+### How to calculate size of inline tree for a given `f`.
+
+Right now we start at a function's inline tree base and
+process inline call data until we hit invalid data. If two inline trees for functions `f` and `j` are next to each other
+with no buffer then `j`'s tree will be mistakenly included in `f`'s tree. The functions that were inlined into `j` 
+will be listed twice as inlined inside `f` as well as `j`. 
+
+### Using pcdata
+
+We don't currently use `funcData.pcdata[PCDATA_InlineTreeIndex]`. 
+Use `funcData.pcdata[PCDATA_InlineTreeIndex]` + `pcHeader.pctabOffset` to go to relevant offset in `pcdata`. 
+(N.B. Some docs call `pcdata` the `pctab`. These are distinct from `pclntab`.)
+The inline tree index could be used to check whether any given PC in a function kicks off inlined function instructions. 
+Since we want every inlined function and are not iterating over every PC in every function, we're not currently using this. HOWEVER. 
+This info might be helpful in determining how many functions were inlined into `f`. We would then be able to separate inline trees.
+
+
+## References
+
+[pclntab structs reference](https://github.com/elastic/otel-profiling-agent/blob/main/docs/gopclntab.md)