[PATCH] D74927: [MC][ARM] make Thumb function also if type attribute is set

[Peter Smith via Phabricator via llvm-commits]

psmith added a comment.

The mapping symbols $a, $t and $d are emitted whenever there is a state change. See the EmitMappingSymbol() functions in ARMELFStreamer.cpp . As an example:

  .thumb
  label:
  bx lr
  .arm
  bx lr
  .type label, %function

would result in an object file with:

  label:
  $t
  bx lr
  $a
  bx lr

The last mapping symbol emitted is cached in LastEMSInfo, and the last mapping symbol for a section is cached in LastMappingSymbols for when ChangeSection() is called. IIUC this doesn't help us very much as LastEMSInfo will only give us the same information as IsThumb. For the example above at the point that the .type label, %function directive were encountered we'd have LastEMSInfo pointing to the $a and IsThumb = false. What we need to do is find the closest mapping symbol at or after label, the "$t" in this case. I can think of a couple of approaches:
1.) Set up a map from MCSymbol to EmitMappingSymbolInfo that records the first "$a" or "$t" mapping symbol seen after each Symbol, if we then encounter a .type symbol, %function we can look up the state.
2.) All symbols, including mapping symbols will be stored in MCAssembler::Symbols. These are accessible via symbol_begin(), symbol_end() and symbols(). In theory we could walk the symbols in reverse on encountering the .type directive, stopping when we encounter the label we are setting the .type for. There are some details that will need to be resolved; symbols, including mapping symbols that are pending, will need to be flushed. I'm making the assumption that symbols are added to MCAssembler::Symbols in source order, but this will need to be checked.

Apologies for all the details, there may be a simpler way of doing this.


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  https://reviews.llvm.org/D74927/new/

https://reviews.llvm.org/D74927