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ccompilationobjdump

llvm objdump: generated assembler not intermixed with C source despite using --source. Why?

I can't seem to generate assembler with intermixed C source with assembler when using Apple LLVM objdump on macOS Sonoma with the --source objdump option. What am I missing?

Environment:

  • OS: macOS Sonoma 14.5, Apple M2

  • cc --version:

    Apple clang version 15.0.0 (clang-1500.3.9.4)
Target: arm64-apple-darwin23.5.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

  • objdump --version:

    Apple LLVM version 15.0.0
Optimized build.
Default target: arm64-apple-darwin23.5.0
Host CPU: apple-m1

  • compilation and objdump command lines I used:

    cc FILE.c -o FILE
objdump --disassemble --demangle --source --no-addresses FILE > FILE.asm
    • Where FILE is the name of a single C file program executable output file name.

With FILE being hello, hello.c being present, I end up with the hello executable and hello.asm. Same for other larger single-file C programs. I can see the ARM assembler code, but I never get the embedded C source inside the objdump output.

I looked for bug reports in LLVM but did not find any. Is there a problem with the command line options I used?

Solution

  • The issue is your compile command:

    cc FILE.c -o FILE

    You cannot extract what you don't put in the file. Normally, debug information (like the coresponding source file and line for a given instruction) is not included in created output file.

    You can tell the compiler to add this information using option -g.