[PATCH v2] ld: Check input section garbage collection error

On Thu, Aug 6, 2026 at 7:04 AM Alan Modra <[email protected]> wrote:
>
> On Thu, Aug 06, 2026 at 05:24:14AM +0800, H.J. Lu wrote:
> > On Wed, Aug 5, 2026 at 6:40 PM Jan Beulich <[email protected]> wrote:
> > >
> > > On 05.08.2026 12:32, H.J. Lu wrote:
> > > > On Wed, Aug 5, 2026 at 4:59 PM Jan Beulich <[email protected]> wrote:
> > > >>
> > > >> On 05.08.2026 10:50, H.J. Lu wrote:
> > > >>> bfd_gc_sections may return false on invalid input:
> > > >>>
> > > >>> ld: pr34448-bug_18.o: bad reloc symbol index (0xf2000005 >= 0x13) for
> > > >>> offset 0x4 in section `.text.get_tls[get_tls]'
> > > >>>
> > > >>> and set the BFD error to bfd_error_bad_value.  Check bfd_gc_sections
> > > >>> return and report the fatal error if the BFD error is bfd_error_bad_value.
> > > >>
> > > >> And what guarantees that bfd_error_bad_value isn't also set for other kinds
> > > >> of errors, from about anywhere in the library? Does bfd_gc_sections()
> > > >> returning false even reliably set the error indicator? That's far from
> > > >
> > > > If it isn't the case, it is a bug.
> > > >
> > > >> obvious when looking at e.g. bfd_elf_gc_sections(), so I can't exclude the
> > > >> possibility of bfd_error_bad_value having been on record before the call,
> > > >> and it simply not getting changed.
> > > >
> > > > Isn't it a bug?
> > >
> > > I don't know, as I don't know enough of the history of libbfd. The value could
> > > be meant to be errno-like, i.e. you may need to clear it at certain points
> > > (especially if there's a mix of functions storing into and not storing into
> > > the field).
> >
> > When a bfd function returns an error, the BFD error should be set
> > appropriately.  If it isn't the case, it is a BFD bug.
>
> The original commits 303b4cc64fa8 and 71b012a810fd omitted
> checking the return from bfd_gc_sections, but I'm inclined to think
> that any false return from bfd_gc_sections should result in an error
> exit from ld, displaying the bfd error with %E.  We also should not be
> ignoring a false return from gc_mark_extra_sections in
> bfd_elf_gc_sections.
>
> --
> Alan Modra

Here is the v2 patch to check gc_mark_extra_sections error return.
With

commit 44fab92685fd1f4bc02cc6668237883ed0d9789d
Author: H.J. Lu <[email protected]>
Date:   Thu Jul 30 15:18:42 2026 +0800

    ld: Don't treated the fatal error as warning

the fatal error won't be ignored by -w.

-- 
H.J.
---
The ELF backend gc_mark_extra_sections function may return false for
error and bfd_gc_sections may return false on invalid input:

ld: pr34448-bug_18.o: bad reloc symbol index (0xf2000005 >= 0x13) for
offset 0x4 in section `.text.get_tls[get_tls]'

and set the BFD error to bfd_error_bad_value.

Change bfd_elf_gc_sections to return false if gc_mark_extra_sections
return false.  Change lang_gc_sections to check bfd_gc_sections return
and report the fatal error if the BFD error is bfd_error_bad_value.

bfd/
PR ld/34448
* elflink.c (bfd_elf_gc_sections): Return false if
gc_mark_extra_sections return false.

ld/
PR ld/34448
* ldlang.c (lang_gc_sections): Check bfd_gc_sections return and
report the fatal error if the BFD error is bfd_error_bad_value.

From a311b4e8150b6f24bd5d99eee525513624754c9a Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <[email protected]>
Date: Wed, 5 Aug 2026 16:43:05 +0800
Subject: [PATCH v2] ld: Check input section garbage collection error

The ELF backend gc_mark_extra_sections function may return false for
error and bfd_gc_sections may return false on invalid input:

ld: pr34448-bug_18.o: bad reloc symbol index (0xf2000005 >= 0x13) for offset 0x4 in section `.text.get_tls[get_tls]'

and set the BFD error to bfd_error_bad_value.

Change bfd_elf_gc_sections to return false if gc_mark_extra_sections
return false.  Change lang_gc_sections to check bfd_gc_sections return
and report the fatal error if the BFD error is bfd_error_bad_value.

bfd/
	PR ld/34448
	* elflink.c (bfd_elf_gc_sections): Return false if
	gc_mark_extra_sections return false.

ld/
	PR ld/34448
	* ldlang.c (lang_gc_sections): Check bfd_gc_sections return and
	report the fatal error if the BFD error is bfd_error_bad_value.

Signed-off-by: H.J. Lu <[email protected]>
---
 bfd/elflink.c | 3 ++-
 ld/ldlang.c   | 6 ++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/bfd/elflink.c b/bfd/elflink.c
index 31c652b17c9..343fc880cda 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -14776,7 +14776,8 @@ bfd_elf_gc_sections (bfd *obfd, struct bfd_link_info *info)
     }
 
   /* Allow the backend to mark additional target specific sections.  */
-  obed->gc_mark_extra_sections (info, gc_mark_hook);
+  if (!obed->gc_mark_extra_sections (info, gc_mark_hook))
+    return false;
 
   /* ... and mark SEC_EXCLUDE for those that go.  */
   return elf_gc_sweep (obfd, info);
diff --git a/ld/ldlang.c b/ld/ldlang.c
index 886c49a1861..f8e9d2496a4 100644
--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -8165,8 +8165,10 @@ lang_gc_sections (void)
 	}
     }
 
-  if (link_info.gc_sections)
-    bfd_gc_sections (link_info.output_bfd, &link_info);
+  if (link_info.gc_sections
+      && !bfd_gc_sections (link_info.output_bfd, &link_info)
+      && bfd_get_error () == bfd_error_bad_value)
+    fatal (_("%P: --gc-sections failed: %E\n"));
 }
 
 /* Worker for lang_find_relro_sections_1.  */
-- 
2.55.0