On 04/05/2021 14:39, Matthias Klose wrote: > Using -flto exposes some new warnings in code, as seen in the both build logs > below, for upstream elfutils and systemd. I have seen others. These > upstreams > enable -Werror by default, but probably don't see these warnings turning to > errors themself, because the LTO flags are usually injected by the packaging > tools. > > e.g. > https://launchpadlibrarian.net/536740411/buildlog_ubuntu-hirsute-ppc64el.systemd_248.666.gd4d7127d94+21.04.20210503043716_BUILDING.txt.gz > e.g. > https://launchpadlibrarian.net/536683989/buildlog_ubuntu-hirsute-amd64.elfutils_0.183.43.g92980edc+21.04.20210502190301_BUILDING.txt.gz > > showing: > > ../src/shared/efi-loader.c: In function ‘efi_get_reboot_to_firmware’: > ../src/shared/efi-loader.c:168:16: error: ‘b’ may be used uninitialized in > this > function [-Werror=maybe-uninitialized] > > i386_lex.c: In function ‘i386_restart’: > i386_lex.c:1816:25: error: potential null pointer dereference > [-Werror=null-dereference] > 1816 | b->yy_bs_column = 0; > > A coworker worked out by review that these warnings are false positives. Now > the first option already has the *maybe* in it's name, the second option gives > this hint in the message (*potentially*). Now getting the complaint that > -Werror isn't usable with -flto anymore. > > Would it make sense to mark warnings with a high potential of false positives, > which are not turned into errors with -Werror? And only turn these into errors > with a new option, e.g. -Wall-errors? > > Matthias >
I don't think that would make sense. Compiling with -Werror is only appropriate if you have a specific compiler version and a specific set of warning flags - otherwise new warnings (either from different flags, or a different compiler version) may cause your build to fail. That's the price you pay for the benefits of static error analysis and for using -Werror to ensure that your code is checked against your set of warnings. Personally, I use -Werror in my own builds - but like most warning-related flags, it is a flag you use during development (and thus the solution in this case is probably to fix the possible issue in the code), not for a bundle of known-good code for distribution and builds. (That's my opinion on such flags. Other opinions are available elsewhere :-) ) David
