* Jason Merrill: > On 6/30/25 5:22 PM, Florian Weimer wrote: >> * Jason Merrill: >> >>> On 6/28/25 3:17 PM, Florian Weimer wrote: >>>> * Jason Merrill: >>>> >>>>> Since r10-6069[1] we control the call to __cxa_finalize with >>>>> DEFAULT_USE_CXA_ATEXIT, so there's no need to also declare it as a weak >>>>> reference; if the target has __cxa_atexit, it must also have >>>>> __cxa_finalize. >> >>>> I expect that most targets do not need __cxa_finalize. They can run >>>> the registered destructors directly, without waiting for a call to >>>> __cxa_finalize. >>> >>> AFAICT glibc still uses __cxa_finalize to run destructors on dlclose; >>> at least that's what its comment says. >> Yes, but for most target processors, there is a variety of targets >> which >> don't do this (no dlclose …), hence “most targets” is still true. >> Maybe. 8-) > > But if those targets don't have dlclose, they don't need __cxa_atexit > and should (and probably do) leave default_use_cxa_atexit off in > config.gcc.
Hmm, that's a fair point. I didn't realize that they could use atexit directly. >>>> I think with your patch, libc will is always linked in as well, >>>> assuming that it's the source of the __cxa_finalize definition. >>> >>> True, so that's not a difference for __cxa_atexit targets. >> Existing targets that reuse the glibc toolchain will have to do >> something about __cxa_finalize after your change goes in, though. > > If they're linking shared libraries (which seems unlikely in your > bootloader scenario below). It just occurred to me that linking shared libraries usually doesn't use -Wl,-z,defs yet, so you would just get underlinking as before. So -nostartfiles probably is not needed after all. >> I'm not sure if that's what our users expect. Common practice is to >> use *-linux-gnu targets to build bootloaders, kernels and whatnot >> using the same toolchain, and not create a separate *-none target >> with different configure options. I think that's … not great for >> full libc targets (where the toolchain may end up supporting >> GNU-style symbol versions, but the dynamic linker does not). But for >> more limited bootloader-type scenarios (no full libc, no dynamic >> linking), it evidently works quite well so far. > > Interesting point, are there in fact such packages that rely on > -fno-use-cxa-atexit? I found this one: <https://sources.debian.org/src/firefox-esr/128.12.0esr-1/third_party/libwebrtc/build/config/coverage/BUILD.gn/?hl=31#L31> Possibly more could be discovered by poking around in Debian Code Search <https://codesearch.debian.net/search?q=fno-use-cxa-atexit&literal=1>. Thanks, Florian
