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Date: Thu, 16 Jun 2022 19:16:59 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106008

            Bug ID: 106008
           Summary: [12 Regression] warning: =E2=80=98(((char *)loadcmds.11=
3_68 +
                    _933 + 16))[329406144173384849].mapend=E2=80=99 may be =
used
                    uninitialized [-Wmaybe-uninitialized]
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
  Target Milestone: ---

Created attachment 53156
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D53156&action=3Dedit
A testcase

When building glibc master branch with -mavx512f, I got

[hjl@gnu-tgl-2 tmp]$ gcc -O2 -march=3Dx86-64 -S -Wall x.i -mavx512f=20
dl-load.c: In function =E2=80=98_dl_map_object_from_fd.constprop=E2=80=99:
dl-load.c:1158:30: warning: =E2=80=98(((char *)loadcmds.113_68 + _933 +
16))[329406144173384849].mapend=E2=80=99 may be used uninitialized
[-Wmaybe-uninitialized]
[hjl@gnu-tgl-2 tmp]$=20

The code looks like

          struct loadcmd *c =3D &loadcmds[nloadcmds++];
          c->mapstart =3D ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize));
          c->mapend =3D ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pages=
ize));
          c->dataend =3D ph->p_vaddr + ph->p_filesz;
          c->allocend =3D ph->p_vaddr + ph->p_memsz;
          /* Remember the maximum p_align.  */
          if (powerof2 (ph->p_align) && ph->p_align > p_align_max)
            p_align_max =3D ph->p_align;
          c->mapoff =3D ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));

          /* Determine whether there is a gap between the last segment
             and this one.  */
          if (nloadcmds > 1 && c[-1].mapend !=3D c->mapstart)
            has_holes =3D true;

c[-1].mapend should always be initialized.=