Re: Reducing debug info for stack traces, while preserving for gdb
For example to give you some context. This is an example small app, the actual app is significantly larger (binary with debug symbols is about 20MB, without debug symbols only 2-3MB). ``` $ ~/bloaty/build/bloaty binary-O3-g-g3-gz # (original binary) FILE SIZEVM SIZE -- -- 19.8% 107Ki 39.3% 107Ki.text 17.0% 93.0Ki 0.0% 0.strtab 13.3% 72.4Ki 0.0% 0.debug_info # 72kB 12.0% 65.3Ki 23.8% 65.3Ki.dynstr 5.2% 28.5Ki 10.4% 28.5Ki.rodata 5.1% 27.9Ki 10.2% 27.9Ki.eh_frame 5.0% 27.5Ki 0.0% 0.debug_loclists # 27kB 4.5% 24.8Ki 0.0% 0.symtab 3.7% 20.4Ki 0.0% 0.debug_str# 20kB 3.4% 18.5Ki 0.0% 0.debug_line # 18.5kB 3.2% 17.6Ki 6.4% 17.6Ki.dynsym 1.3% 7.25Ki 0.0% 0[Unmapped] 1.2% 6.61Ki 2.1% 5.64Ki[27 Others] 1.1% 6.18Ki 2.3% 6.18Ki.eh_frame_hdr 0.9% 5.08Ki 1.9% 5.08Ki.gnu.hash 0.8% 4.31Ki 1.6% 4.31Ki.data.rel.ro 0.8% 4.12Ki 1.5% 4.12Ki.rela.dyn 0.5% 2.69Ki 0.0% 0[ELF Section Headers] 0.4% 2.38Ki 0.0% 0.debug_rnglists # small 0.3% 1.74Ki 0.0% 0.debug_abbrev # small 0.3% 1.52Ki 0.6% 1.52Ki.rela.plt 100.0% 545Ki 100.0% 273KiTOTAL ``` ``` $ ~/bloaty/build/bloaty binary-O3-g-g1-gz # binary with -g1, and compressed debug sections FILE SIZEVM SIZE -- -- 24.4% 107Ki 39.3% 107Ki.text 21.1% 93.0Ki 0.0% 0.strtab 14.8% 65.3Ki 23.8% 65.3Ki.dynstr 6.5% 28.5Ki 10.4% 28.5Ki.rodata 6.3% 27.9Ki 10.2% 27.9Ki.eh_frame 5.6% 24.8Ki 0.0% 0.symtab 4.0% 17.6Ki 6.4% 17.6Ki.dynsym 3.5% 15.5Ki 0.0% 0.debug_line # smaller 2.8% 12.2Ki 0.0% 0.debug_str # smaller 2.4% 10.4Ki 0.0% 0.debug_info # way smaller 1.6% 7.25Ki 0.0% 0[Unmapped] 1.4% 6.18Ki 2.3% 6.18Ki.eh_frame_hdr 1.2% 5.08Ki 1.9% 5.08Ki.gnu.hash 1.0% 4.31Ki 1.6% 4.31Ki.data.rel.ro 1.0% 4.20Ki 0.9% 2.43Ki[25 Others] 0.9% 4.12Ki 1.5% 4.12Ki.rela.dyn 0.6% 2.56Ki 0.0% 0[ELF Section Headers] 0.3% 1.52Ki 0.6% 1.52Ki.rela.plt 0.3% 1.47Ki 0.5% 1.47Ki.gnu.version 0.2% 1.03Ki 0.4% 1.03Ki.plt 0.2% 728 0.3% 728[ELF Program Headers] 100.0% 441Ki 100.0% 273KiTOTAL ``` (`.debug_rnglists` and `.debug_abbrev` do not even register). ``` $ ~/bloaty/build/bloaty binary-O3-g-g3.exe # without debug sections (broken lines in stack trace) FILE SIZEVM SIZE -- -- 26.9% 107Ki 39.3% 107Ki.text 23.2% 92.9Ki 0.0% 0.strtab 16.3% 65.3Ki 23.8% 65.3Ki.dynstr 7.1% 28.5Ki 10.4% 28.5Ki.rodata 6.9% 27.9Ki 10.2% 27.9Ki.eh_frame 6.2% 24.7Ki 0.0% 0.symtab 4.4% 17.6Ki 6.4% 17.6Ki.dynsym 1.8% 7.25Ki 0.0% 0[Unmapped] 1.5% 6.18Ki 2.3% 6.18Ki.eh_frame_hdr 1.3% 5.08Ki 1.9% 5.08Ki.gnu.hash 1.1% 4.31Ki 1.6% 4.31Ki.data.rel.ro 1.0% 4.12Ki 1.5% 4.12Ki.rela.dyn 0.5% 2.12Ki 0.0% 0[ELF Section Headers] 0.4% 1.52Ki 0.6% 1.52Ki.rela.plt 0.4% 1.47Ki 0.5% 1.47Ki.gnu.version 0.3% 1.18Ki 0.3% 881[18 Others] 0.3% 1.03Ki 0.4% 1.03Ki.plt 0.2% 728 0.3% 728[ELF Program Headers] 0.1% 552 0.2% 552.data 0.1% 544 0.2% 544.got.plt 0.1% 512 0.2% 512.dynamic 100.0% 401Ki 100.0% 273KiTOTAL ``` ``` $ ~/bloaty/build/bloaty binary-O3-g-g3.debug # only debug sections FILE SIZEVM SIZE -- -- 31.0% 178Ki 0.0% 0.debug_info 0.0% 0 39.3% 107Ki.text 18.5% 106Ki 0.0% 0.debug_loclists 16.8% 96.9Ki 0.0% 0.debug_str 16.1% 93.0Ki 0.0% 0.strtab 0.0% 0 23.8% 65.3Ki.dynstr 10.5% 60.7Ki 0.0% 0.debug_line 0.0% 0 10.4% 28.5Ki.rodata 0.0% 0 10.2% 27.9Ki.eh_frame 4.3% 24.8Ki 0.0% 0.symtab 0.0% 0 6.4% 17.6Ki.dynsym 0.0% 0 2.3% 6.18Ki.eh_frame_hdr 1.0% 5.86Ki 0.0% 0.debug_rnglists 0.0% 0 1.9% 5.08Ki.gnu.hash 0.8% 4.54Ki 0.0% 0.debug_abbrev 0.0% 0 1.6% 4.31Ki.data.rel.ro 0.5% 2.79Ki 1.5% 4.17Ki[27 Others] 0.0% 0 1.5% 4.12Ki.rela.dyn 0.5% 2.69Ki 0.0% 0[ELF Section Headers] 0.0% 0 0.6% 1.52Ki.rela.plt 0.0% 0 0.5% 1.47Ki
Reducing debug info for stack traces, while preserving for gdb
Hi, I am trying to split debug symbols out of final binary, to reduce its size. But I would like to preserve at least line numbers in the stacktraces from `Exception`s. Linux, amd64. gdc 12.2.0 on Debian testing. Binary is compiled using `-O3 -g -g3` (and possibly -gz). I then use `objcopy` to split debug info from final ELF binary file into .exe and .debug files. I use `objcopy --only-keep-debug --compress-debug-sections=zlib binary binary.debug` to produce .debug file. Then I use normally `objcopy --strip-debug binary binary.exe` (possibly with --compress-debug-sections=zlib) to produce binary. This makes it possibly to use in gdb without issues (using `gdb -s binary.debug -e binary` for example, or by utilizing `--add-gnu-debuglink=` option in `objcopy`). But this causes stacktraces to miss line numbers (and columns). (function names are still there, as these are derived from symbol tables instead). I tried selectively removing DWARF debug sections, but it looks that at least these are required: `.debug_info` `.debug_aranges` `.debug_abbrev` `.debug_line` `.debug_str` `.debug_line_str` `.debug_rnglists` So, I can only remove these: `objcopy -R .debug_loc -R .debug_macro -R .debug_ranges -R .debug_loclists` (`.debug_loc` and `.debug_ranges` are not even generated by gcc, so it does not matter probably). The issue is, this saves me very little space. `.debug_macro` and `.debug_loclists` are rather small. The bulk of information is in `.debug_info`. But I believe it contains way more information than is really needed to just produce line numbers. I did inspect final binaries , and it is using DWARF version 5. I also tried `-gas-loc-support` , but no change. Using `-g1` makes stack traces work nicely, by making `.debug_info` smaller, but then debugging in `gdb` is very limited. One option would be to compile application twice, once with `-g1` and once with `-g3`. But I really do not think this is supported, or reliable, even if I enable deterministic builds. In one article ( https://support.backtrace.io/hc/en-us/articles/360040105792-DWARF#RemovingDebugInformation ) I read that for C/C++ in GCC, it is enough to preserve only `.debug_frame` and `.debug_line` to get function, source filenames and line numbers. But that is not true for gdc and its stacktrace handler. I did read about this gdb extension, which is interesting, https://sourceware.org/gdb/onlinedocs/gdb/MiniDebugInfo.html , but I did not try, and it is probably only supported in gdb (i.e. addr2libe, Phobos, libunwind do not support it). Any ideas?
