On Wed, Mar 12, 2025 at 2:36 AM Ben Hutchings <ben@xxxxxxxxxxxxxxx> wrote: > > On Tue, 2025-03-11 at 20:03 +0900, Masahiro Yamada wrote: > > On Mon, Feb 17, 2025 at 10:23 PM Miguel Ojeda > > <miguel.ojeda.sandonis@xxxxxxxxx> wrote: > > > > > > On Mon, Feb 10, 2025 at 6:11 PM Thomas Weißschuh <linux@xxxxxxxxxxxxxx> wrote: > > > > > > > > Remap source path prefixes in all output, including compiler > > > > diagnostics, debug information, macro expansions, etc. > > > > > > Hmm... We don't do all the cases in the C side -- the docs ask to use > > > `KCFLAGS` when one wants to remove them in the debug info: > > > > > > https://docs.kernel.org/kbuild/reproducible-builds.html#absolute-filenames > > > > > > I am not sure if there is a reason not to cover all cases in C (Cc'ing Ben). > > I think we should use the prefix-map options by default, for both C and > Rust code. A patch is appreciated. (top-level Makefile change with updates in Documentation/kbuild/reproducible-builds.rst) > > The default of using absolute filenames only works when the build and > debug systems have their sources in the same absolute directory. For > some developers this will always be true because they're the same > system. In the general case, and particularly in production, it's > unlikely to be true. See below. > > > GCC manual mentions the below about the -fdebug-prefix-map=old=new > > > > > > "It can also be used to change an absolute path to > > a relative path by using . for new. > > This can give more reproducible builds, which are location > > independent, but may require an extra command to tell GDB > > where to find the source files." > > > > > > I guess "the extra command" might be a bit annoying. > > The command in question is "dir <source-root-directory>". It's not > particulary annoying. It also isn't needed when invoking gdb with the > kernel source root as its current directory. > > Running that command adds the directory to gdb's source search path, > causing it to look for sources referenced in debug info by: > > 1. Appending the full filename to that directory > 2. Appending the base filename to that directory > > (This is slightly simplified from the docuemntation at: > <https://sourceware.org/gdb/current/onlinedocs/gdb.html/Source-Path.html#Source-Path>.) > > When the debug info has relative filenames, case 1 should always work. > > When the debug info has absolute filenames, case 2 can work if all > sources are in the same directory. But the kernel has source files > spread across many directories, so there's no general way to make gdb > find them all. > > Ben. > > -- > Ben Hutchings > A free society is one where it is safe to be unpopular. > - Adlai Stevenson -- Best Regards Masahiro Yamada
