[llvm-bugs] [Bug 44522] New: “-use-unknown-locations” option support is missing for Codeview debug info

via llvm-bugs llvm-bugs at lists.llvm.org
Sat Jan 11 19:08:29 PST 2020


            Bug ID: 44522
           Summary: “-use-unknown-locations” option support is missing for
                    Codeview debug info
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: steven.shi at intel.com
                CC: llvm-bugs at lists.llvm.org

Problem Background: 
We meet an LLD PDB issue that if we link assembly code with C code and set >=
-O1 level optimization, the executable's PDB will contain wrong zero Lines for
the assembly code in DEBUG_S_LINES subsection, and then our COFF source
debuggers will fail to do the source-level debug on the executable. 

I checked the LLVM master code and find that the “-use-unknown-locations”
option and its related logic is only supported in Dwarf debug info as below.
These codes are missing in the Codeview side. It looks the
“-use-unknown-locations” option logic is not complex, could we port the code
logic into  llvm\lib\CodeGen\AsmPrinter\CodeViewDebug.cpp as well?

... ...
static cl::opt<DefaultOnOff> UnknownLocations(
    "use-unknown-locations", cl::Hidden,
    cl::desc("Make an absence of debug location information explicit."),
    cl::values(clEnumVal(Default, "At top of block or after label"),
               clEnumVal(Enable, "In all cases"), clEnumVal(Disable, "Never")),
... ... 
    // If user said Don't Do That, don't do that.
    if (UnknownLocations == Disable)

This issue blocks the LLVM toolchain debugging capability for UEFI firmware.
Please help to add the support. Thank you in advance!

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