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From FEDORA_PATCHES Mon Sep 17 00:00:00 2001
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From: Keith Seitz <keiths@redhat.com>
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Date: Thu, 25 Mar 2021 10:31:48 -0700
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Subject: gdb-rhbz1931344-bfd_seek-elf_read_notes.patch
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;; Backport "Save/restore file offset while reading notes in core file"
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;; (Keith Seitz, RHBZ 1931344)
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A recent bug (RH BZ 1931344) has exposed a bug in the core file
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build-ID support that I introduced a while ago. It is pretty
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easy to demonstate the problem following a simplified procedure
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outlined in that bug:
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[shell1]
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shell1$ /usr/libexec/qemu-kvm
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[shell2]
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shell2$ pkill -SEGV -x qemu-kvm
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[shell1]
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Segmentation fault (core dumped)
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Load this core file into GDB without specifying an executable
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(an unfortunate Fedora/RHEL-ism), and GDB will inform the user
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to install debuginfo for the "missing" executable:
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$ gdb -nx -q core.12345
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...
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Missing separate debuginfo for the main executable file
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Try: dnf --enablerepo='*debug*' install /usr/lib/debug/.build-id/e2/e9c66d3117fb2bbb5b2be122f04f2664e5df54
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Core was generated by `/usr/libexec/qemu-kvm'.
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Program terminated with signal SIGSEGV, Segmentation fault.
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...
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The suggested build-ID is actaully for gmp not qemu-kvm. The problem
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lies in _bfd_elf_core_find_build_id, where we loop over program headers
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looking for note segments:
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/* Read in program headers and parse notes. */
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for (i = 0; i < i_ehdr.e_phnum; ++i, ++i_phdr)
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{
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Elf_External_Phdr x_phdr;
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if (bfd_bread (&x_phdr, sizeof (x_phdr), abfd) != sizeof (x_phdr))
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goto fail;
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elf_swap_phdr_in (abfd, &x_phdr, i_phdr);
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if (i_phdr->p_type == PT_NOTE && i_phdr->p_filesz > 0)
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{
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elf_read_notes (abfd, offset + i_phdr->p_offset,
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i_phdr->p_filesz, i_phdr->p_align);
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if (abfd->build_id != NULL)
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return TRUE;
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}
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elf_read_notes uses bfd_seek to forward the stream to the location of
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the note segment. When control returns to _bfd_elf_core_fild_build_id,
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the stream is no longer in the location looking at program headers, and
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all subsequent reads will read from the wrong file offset.
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To fix this, this patch marks the stream location and ensures
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that it is restored after elf_read_notes is called.
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bfd/ChangeLog
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2021-03-26 Keith Seitz <keiths@redhat.com>
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* elfcore.h (_bfd_elf_core_find_build_id): Seek file
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offset of program headers after calling elf_read_notes.
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diff --git a/bfd/elfcore.h b/bfd/elfcore.h
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--- a/bfd/elfcore.h
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+++ b/bfd/elfcore.h
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@@ -410,6 +410,13 @@ NAME(_bfd_elf, core_find_build_id)
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{
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elf_read_notes (abfd, offset + i_phdr->p_offset,
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i_phdr->p_filesz, i_phdr->p_align);
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+
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+ /* Make sure ABFD returns to processing the program headers. */
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+ if (bfd_seek (abfd, (file_ptr) (offset + i_ehdr.e_phoff
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+ + (i + 1) * sizeof (x_phdr)),
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+ SEEK_SET) != 0)
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+ goto fail;
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+
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if (abfd->build_id != NULL)
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return TRUE;
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}
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