How can I tell if a binary was compiled with debug symbols?

Linux

Check whether it contains the .debug... sections:

$ readelf -S <binary> | grep .debug
  [30] .debug_info       PROGBITS         0000000000000000  0001404c
  [31] .debug_abbrev     PROGBITS         0000000000000000  0003ddbe
  [32] .debug_aranges    PROGBITS         0000000000000000  0003f81f
  [33] .debug_ranges     PROGBITS         0000000000000000  00041c0f
  [34] .debug_line       PROGBITS         0000000000000000  000440af
  [35] .debug_str        PROGBITS         0000000000000000  00048e3b

Mac

dsymutil -s <binary> | grep N_OSO

... should produce non-empty output.

Windows

• When compiling with MS Visual C++, or targeting -msvc with Rust, check whether a <binary>.pdb file exists next to the binary. You may also use the symchk utility to locate/validate debug symbols.
• When compiling with MinGW, or targeting -gnu with Rust, the debugging symbols will be stored in .debug... sections, just like in the Linux case. Use tools like dumpbin /headers <binary> or objdump -P sections <binary> to confirm that these sections exist.