Debug info on macOS
Hi, I'm developing Emacs using its native compilation on macOS, which is based on libgccjit. In this context, I'm currently failing to get .eln files (= .so, .dylib, .dll depending on the platform) with debug info. This has probably its roots in the special handling of DWARF under macOS, a long-winded story leading to dSYM bundles... My question is: can I somehow configure libgccjit in a way that keeps the .o file that was used to produce the resulting .dylib, like it keeps/writes the various intermediate files that one can get? If that's possible, my hope would be to extract the debug info from the .o using dsymutil and use that with the .dylib. TIA!
Re: Debug info on macOS
David Malcolm writes: > As I understand it, Emacs is using libgccjit to do ahead-of-time > compilation, presumably compiling the optimized ELisp code to machine > code as a shared library. Correct. > Is Emacs using gcc_jit_context_compile_to_file with > GCC_JIT_OUTPUT_KIND_DYNAMIC_LIBRARY, or is it doing something more > complicated? Yes. (Sorry, I forgot to CC Andrea; he sent me here :-)). > If that's what it's doing, you might want to take a look > at playback::context::compile in gcc/jit-playback.cc (and try stepping > through it in the debugger). In particular, the > playback::compile_to_file::postprocess implementation of the > playback::context::postprocess vfunc is responsible for taking a .s in > a tempdir and turning it into the desired output. Perhaps there's some > macOS-specific special-casing needed there? > > You might also find it useful to look at the overview of how > libgccjit's internals here: > https://gcc.gnu.org/onlinedocs/jit/internals/index.html#overview-of-code-structure > > Hope this is helpful Yes it is. Thanks, David!
Re: Debug info on macOS
On 2024-05-11 05:39, Gerd Möllmann wrote: David Malcolm writes: As I understand it, Emacs is using libgccjit to do ahead-of-time compilation, presumably compiling the optimized ELisp code to machine code as a shared library. Correct. Is Emacs using gcc_jit_context_compile_to_file with GCC_JIT_OUTPUT_KIND_DYNAMIC_LIBRARY, or is it doing something more complicated? Yes. (Sorry, I forgot to CC Andrea; he sent me here :-)). If that's what it's doing, you might want to take a look at playback::context::compile in gcc/jit-playback.cc (and try stepping through it in the debugger). In particular, the playback::compile_to_file::postprocess implementation of the playback::context::postprocess vfunc is responsible for taking a .s in a tempdir and turning it into the desired output. Perhaps there's some macOS-specific special-casing needed there? You might also find it useful to look at the overview of how libgccjit's internals here: https://gcc.gnu.org/onlinedocs/jit/internals/index.html#overview-of-code-structure Hope this is helpful Yes it is. Thanks, David! Found something out. Passing -save-temps=obj to libgccjit makes it keep the .o file used to compile the .eln dylibs in Emacs/macOS. Libgccjit then performs the same way gcc-14 does on macOS when compiling with -g. Maybe one could check what gcc-14 does for -g on macOS, and do the same when libgccjit compiles with debug > 0. I'm not familiar enough with GCC to do that in a reasoanble time, sorry. And I can't build it easily.
