On Wed, Mar 8, 2023 at 2:04 PM Martin Liška <mli...@suse.cz> wrote: > > On 3/3/23 12:12, Richard Biener via Gcc-patches wrote: > > On Fri, Mar 3, 2023 at 9:30 AM Alexandre Oliva <ol...@adacore.com> wrote: > >> > >> On Feb 17, 2023, Richard Biener <richard.guent...@gmail.com> wrote: > >> > >>>> * gimple-ssa-warn-access.cc > >>>> (pass_waccess::check_dangling_stores): Skip non-stores. > >>>> > >>>> for gcc/testsuite/ChangeLog > >>>> > >>>> * g++.dg/warn/Wdangling-pointer.C (warn_init_ref_member): Add > >>>> two new variants, one fixed, one xfailed. > >>>> * c-c++-common/Wdangling-pointer-5.c > >>>> (nowarn_store_arg_store_arg): Add now-expected warnings. > >> > >> Ping? > >> https://gcc.gnu.org/pipermail/gcc-patches/2023-February/612186.html > > > > I was hoping Martin would chime in, but he didn't. > > > > So - OK. > > > > Thanks, > > Richard. > > > >> > >> -- > >> Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ > >> Free Software Activist GNU Toolchain Engineer > >> Disinformation flourishes because many people care deeply about injustice > >> but very few check the facts. Ask me about <https://stallmansupport.org> > > Hi. > > I've just noticed this change triggered one more warning for qemu 7.1.0: > > cc -m64 -mcx16 -Ilibqemuutil.a.p -I. -I.. -Isubprojects/libvhost-user > -I../subprojects/libvhost-user -Iqapi -Itrace -Iui -Iui/shader > -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/libmount > -I/usr/include/blkid -I/usr/include/gio-unix-2.0 -I/usr/include/p11-kit-1 > -I/usr/include/pixman-1 -fdiagnostics-color=auto -Wall -Winvalid-pch -Werror > -std=gnu11 -O2 -isystem /home/abuild/rpmbuild/BUILD/qemu-7.1.0/linux-headers > -isystem linux-headers -iquote . -iquote > /home/abuild/rpmbuild/BUILD/qemu-7.1.0 -iquote > /home/abuild/rpmbuild/BUILD/qemu-7.1.0/include -iquote > /home/abuild/rpmbuild/BUILD/qemu-7.1.0/tcg/i386 -pthread -D_GNU_SOURCE > -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -Wstrict-prototypes > -Wredundant-decls -Wundef -Wwrite-strings -Wmissing-prototypes > -fno-strict-aliasing -fno-common -fwrapv -Wold-style-declaration > -Wold-style-definition -Wtype-limits -Wformat-security -Wformat-y2k > -Winit-self -Wignored-qualifiers -Wempty-body -Wnested-externs -Wendif-labels > -Wexpansion-to-defined -Wimplicit-fallthrough=2 -Wno-missing-include-dirs > -Wno-shift-negative-value -Wno-psabi -fstack-protector-strong -O2 -Wall > -fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables > -fstack-clash-protection -Werror=return-type -U_FORTIFY_SOURCE > -D_FORTIFY_SOURCE=2 -fPIE -MD -MQ libqemuutil.a.p/util_async.c.o -MF > libqemuutil.a.p/util_async.c.o.d -o libqemuutil.a.p/util_async.c.o -c > ../util/async.c > In file included from > /home/abuild/rpmbuild/BUILD/qemu-7.1.0/include/qemu/coroutine.h:18, > from > /home/abuild/rpmbuild/BUILD/qemu-7.1.0/include/block/aio.h:20, > from ../util/async.c:28: > ../util/async.c: In function 'aio_bh_poll': > /home/abuild/rpmbuild/BUILD/qemu-7.1.0/include/qemu/queue.h:303:22: error: > storing the address of local variable 'slice' in > '*ctx.bh_slice_list.sqh_last' [-Werror=dangling-pointer=] > 303 | (head)->sqh_last = &(elm)->field.sqe_next; > \ > | ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~ > ../util/async.c:161:5: note: in expansion of macro 'QSIMPLEQ_INSERT_TAIL' > 161 | QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, &slice, next); > | ^~~~~~~~~~~~~~~~~~~~ > ../util/async.c:156:17: note: 'slice' declared here > 156 | BHListSlice slice; > | ^~~~~ > ../util/async.c:156:17: note: 'ctx' declared here > > which I reduced to: > > $ cat util_async.i > typedef struct BHListSlice BHListSlice; > struct BHListSlice { > struct { > BHListSlice *sqe_next; > } next; > } *aio_bh_poll_s; > struct AioContext { > struct { > BHListSlice *sqh_first; > BHListSlice **sqh_last; > } bh_slice_list; > } aio_bh_dequeue(); > int aio_bh_poll_bh; > int aio_bh_poll(struct AioContext *ctx) { > BHListSlice slice; > (&ctx->bh_slice_list)->sqh_last = &(slice.next.sqe_next); > while (aio_bh_poll_s) { > unsigned flags; > aio_bh_dequeue(&flags); > if (aio_bh_poll_bh) { > (&ctx->bh_slice_list)->sqh_last = &(&ctx->bh_slice_list)->sqh_first; > continue; > } > } > return 0; > } > > $ gcc util_async.i -c -Werror=dangling-pointer > util_async.i: In function ‘aio_bh_poll’: > util_async.i:16:35: error: storing the address of local variable ‘slice’ in > ‘*ctx.bh_slice_list.sqh_last’ [-Werror=dangling-pointer=] > 16 | (&ctx->bh_slice_list)->sqh_last = &(slice.next.sqe_next); > | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~ > util_async.i:15:15: note: ‘slice’ declared here > 15 | BHListSlice slice; > | ^~~~~ > util_async.i:15:15: note: ‘ctx’ declared here > cc1: some warnings being treated as errors > > Is the emitted warning correct?
For the reduced testcase yes, if !aio_bh_poll_s (or !aio_bh_poll_bh) the stored pointer remains local. But I can imagine this to be known (to the programmer) to not happen for the original code and eventually GCC jump-threading some never reachable path (we've been there before). Richard. > Thank you, > Martin
