diff mbox series

[v2] elf: Silence GCC 12 false positive warning

Message ID 20220617015718.1086832-1-hjl.tools@gmail.com
State Superseded
Headers
Series [v2] elf: Silence GCC 12 false positive warning |

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Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent
dj/TryBot-32bit success Build for i686

Commit Message

H.J. Lu June 17, 2022, 1:57 a.m. UTC 
  Silence GCC 12 false positive warning with -mavx512f on dl-load.c:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106008

$ gcc -O2 -fPIC -march=x86-64 -mavx512f -S -Wall ...
dl-load.c: In function ‘_dl_map_object_from_fd.constprop’:
dl-load.c:1158:30: warning: ‘(((char *)loadcmds.113_68 + _933 + 16))[329406144173384849].mapend’ may be used uninitialized [-Wmaybe-uninitialized]
---
 elf/dl-load.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

Comments

Noah Goldstein June 17, 2022, 2:31 a.m. UTC | #1 
On Thu, Jun 16, 2022 at 6:57 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> Silence GCC 12 false positive warning with -mavx512f on dl-load.c:
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106008
>
> $ gcc -O2 -fPIC -march=x86-64 -mavx512f -S -Wall ...
> dl-load.c: In function ‘_dl_map_object_from_fd.constprop’:
> dl-load.c:1158:30: warning: ‘(((char *)loadcmds.113_68 + _933 + 16))[329406144173384849].mapend’ may be used uninitialized [-Wmaybe-uninitialized]
> ---
>  elf/dl-load.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index 2e4a010fc5..806d7a9a62 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -1152,11 +1152,21 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
>             p_align_max = ph->p_align;
>           c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
>
> +         DIAG_PUSH_NEEDS_COMMENT;
> +
> +#if __GNUC_PREREQ (12, 0)
> +         /* Suppress valid GCC warning:
> +            ‘(((char *)loadcmds.113_68 + _933 + 16))[329406144173384849].mapend’ may be used uninitialized [-Wmaybe-uninitialized]
> +          */
> +         DIAG_IGNORE_NEEDS_COMMENT (12, "-Wmaybe-uninitialized");
> +#endif

I get this issue with CC="gcc-11 x86-64-v4" aswell.
>           /* Determine whether there is a gap between the last segment
>              and this one.  */
>           if (nloadcmds > 1 && c[-1].mapend != c->mapstart)
>             has_holes = true;
>
> +         DIAG_POP_NEEDS_COMMENT;
> +
>           /* Optimize a common case.  */
>  #if (PF_R | PF_W | PF_X) == 7 && (PROT_READ | PROT_WRITE | PROT_EXEC) == 7
>           c->prot = (PF_TO_PROT
> --
> 2.36.1
>
Noah Goldstein June 17, 2022, 2:39 a.m. UTC | #2 
On Thu, Jun 16, 2022 at 7:31 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> On Thu, Jun 16, 2022 at 6:57 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > Silence GCC 12 false positive warning with -mavx512f on dl-load.c:
> >
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106008
> >
> > $ gcc -O2 -fPIC -march=x86-64 -mavx512f -S -Wall ...
> > dl-load.c: In function ‘_dl_map_object_from_fd.constprop’:
> > dl-load.c:1158:30: warning: ‘(((char *)loadcmds.113_68 + _933 + 16))[329406144173384849].mapend’ may be used uninitialized [-Wmaybe-uninitialized]
> > ---
> >  elf/dl-load.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/elf/dl-load.c b/elf/dl-load.c
> > index 2e4a010fc5..806d7a9a62 100644
> > --- a/elf/dl-load.c
> > +++ b/elf/dl-load.c
> > @@ -1152,11 +1152,21 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> >             p_align_max = ph->p_align;
> >           c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
> >
> > +         DIAG_PUSH_NEEDS_COMMENT;
> > +
> > +#if __GNUC_PREREQ (12, 0)
> > +         /* Suppress valid GCC warning:
> > +            ‘(((char *)loadcmds.113_68 + _933 + 16))[329406144173384849].mapend’ may be used uninitialized [-Wmaybe-uninitialized]
> > +          */
> > +         DIAG_IGNORE_NEEDS_COMMENT (12, "-Wmaybe-uninitialized");
> > +#endif
>
> I get this issue with CC="gcc-11 x86-64-v4" aswell.

No issue with gcc-10.

What about:

#if __GNUC_PREREQ (11, 0) && defined __AVX512F__?
> >           /* Determine whether there is a gap between the last segment
> >              and this one.  */
> >           if (nloadcmds > 1 && c[-1].mapend != c->mapstart)
> >             has_holes = true;
> >
> > +         DIAG_POP_NEEDS_COMMENT;
> > +
> >           /* Optimize a common case.  */
> >  #if (PF_R | PF_W | PF_X) == 7 && (PROT_READ | PROT_WRITE | PROT_EXEC) == 7
> >           c->prot = (PF_TO_PROT
> > --
> > 2.36.1
> >
H.J. Lu June 17, 2022, 2:53 a.m. UTC | #3 
On Thu, Jun 16, 2022 at 7:39 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> On Thu, Jun 16, 2022 at 7:31 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > On Thu, Jun 16, 2022 at 6:57 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > >
> > > Silence GCC 12 false positive warning with -mavx512f on dl-load.c:
> > >
> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106008
> > >
> > > $ gcc -O2 -fPIC -march=x86-64 -mavx512f -S -Wall ...
> > > dl-load.c: In function ‘_dl_map_object_from_fd.constprop’:
> > > dl-load.c:1158:30: warning: ‘(((char *)loadcmds.113_68 + _933 + 16))[329406144173384849].mapend’ may be used uninitialized [-Wmaybe-uninitialized]
> > > ---
> > >  elf/dl-load.c | 10 ++++++++++
> > >  1 file changed, 10 insertions(+)
> > >
> > > diff --git a/elf/dl-load.c b/elf/dl-load.c
> > > index 2e4a010fc5..806d7a9a62 100644
> > > --- a/elf/dl-load.c
> > > +++ b/elf/dl-load.c
> > > @@ -1152,11 +1152,21 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> > >             p_align_max = ph->p_align;
> > >           c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
> > >
> > > +         DIAG_PUSH_NEEDS_COMMENT;
> > > +
> > > +#if __GNUC_PREREQ (12, 0)
> > > +         /* Suppress valid GCC warning:
> > > +            ‘(((char *)loadcmds.113_68 + _933 + 16))[329406144173384849].mapend’ may be used uninitialized [-Wmaybe-uninitialized]
> > > +          */
> > > +         DIAG_IGNORE_NEEDS_COMMENT (12, "-Wmaybe-uninitialized");
> > > +#endif
> >
> > I get this issue with CC="gcc-11 x86-64-v4" aswell.
>
> No issue with gcc-10.
>
> What about:
>
> #if __GNUC_PREREQ (11, 0) && defined __AVX512F__?

This GCC 11/12/13 bug may be triggered with other conditions.
I will change it to

#if __GNUC_PREREQ (11, 0)

> > >           /* Determine whether there is a gap between the last segment
> > >              and this one.  */
> > >           if (nloadcmds > 1 && c[-1].mapend != c->mapstart)
> > >             has_holes = true;
> > >
> > > +         DIAG_POP_NEEDS_COMMENT;
> > > +
> > >           /* Optimize a common case.  */
> > >  #if (PF_R | PF_W | PF_X) == 7 && (PROT_READ | PROT_WRITE | PROT_EXEC) == 7
> > >           c->prot = (PF_TO_PROT
> > > --
> > > 2.36.1
> > >
diff mbox series

Patch

diff --git a/elf/dl-load.c b/elf/dl-load.c
index 2e4a010fc5..806d7a9a62 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1152,11 +1152,21 @@  _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 	    p_align_max = ph->p_align;
 	  c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
 
+	  DIAG_PUSH_NEEDS_COMMENT;
+
+#if __GNUC_PREREQ (12, 0)
+	  /* Suppress valid GCC warning:
+	     ‘(((char *)loadcmds.113_68 + _933 + 16))[329406144173384849].mapend’ may be used uninitialized [-Wmaybe-uninitialized]
+	   */
+	  DIAG_IGNORE_NEEDS_COMMENT (12, "-Wmaybe-uninitialized");
+#endif
 	  /* Determine whether there is a gap between the last segment
 	     and this one.  */
 	  if (nloadcmds > 1 && c[-1].mapend != c->mapstart)
 	    has_holes = true;
 
+	  DIAG_POP_NEEDS_COMMENT;
+
 	  /* Optimize a common case.  */
 #if (PF_R | PF_W | PF_X) == 7 && (PROT_READ | PROT_WRITE | PROT_EXEC) == 7
 	  c->prot = (PF_TO_PROT