Figuring out what to do when a mix of BTF and CTF sections is supplied is a
little magical. We hunt down all the .BTF and .ctf sections in the link,
but just because all the sections we found were .BTF doesn't mean that the
output isn't going to be CTF: if deduplication results in any conflicting
types, we'll need a CTF section to encode them (BTF cannot yet represent
such things).
So if we find that we've got nothing but .BTF sections, we do as we do for
.ctf and mark all but one of them as excluded from the link (with the intent
of creating the deduplicated output in the remaining one): but we also
create a provisional linker-created .ctf section, just in case we need it
later (we can't tell at this stage, before deduplication).
After deduplication, one of these sections is unneeded. Sometimes, we can
do this removal via Depending on the emulation, lang_write_ctf may be called
either early (long before bfd_elf_final_link) or late (after final link and
indeed symtab and strtab writeout). (ELF calls it late). If called early,
we can figure out what format was emitted by ctf_link and freely remove the
unwanted section by flipping on its SEC_EXCLUDE flag.
But that leaves late calls. We add a new ctf_remove_section hook to the
bfd_link_callbacks, which is invoked at the very start of
bfd_elf_final_link, when removal of sections is still permitted. We invoke
section removal for the .ctf-or-.BTF section via this hook if lang_write_ctf
is called late: this then does the extra trickery with section count
adjustment etc needed to remove sections so late, and communicates the fact
that it's removed sections to bfd_elf_final_link, which can then decide to
call _bfd_fix_excluded_sec_syms (which is quite expensive, so we do it only
once for all sections removed at this stage, by whatever means).
This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.
BFD is an object file library. It permits applications to use the
same routines to process object files regardless of their format.
BFD is used by the GNU debugger, assembler, linker, and the binary
utilities.
The documentation on using BFD is scanty and may be occasionally
incorrect. Pointers to documentation problems, or an entirely
rewritten manual, would be appreciated.
There is some BFD internals documentation in doc/bfdint.texi which may
help programmers who want to modify BFD.
BFD is normally built as part of another package. See the build
instructions for that package, probably in a README file in the
appropriate directory.
BFD supports the following configure options:
--target=TARGET
The default target for which to build the library. TARGET is
a configuration target triplet, such as sparc-sun-solaris.
--enable-targets=TARGET,TARGET,TARGET...
Additional targets the library should support. To include
support for all known targets, use --enable-targets=all.
--enable-64-bit-bfd
Include support for 64 bit targets. This is automatically
turned on if you explicitly request a 64 bit target, but not
for --enable-targets=all. This requires a compiler with a 64
bit integer type, such as gcc.
--enable-shared
Build BFD as a shared library.
--with-mmap
Use mmap when accessing files. This is faster on some hosts,
but slower on others. It may not work on all hosts.
Report bugs in BFD to https://sourceware.org/bugzilla/
Patches are encouraged. When sending patches, always send the output
of diff -u or diff -c from the original file to the new file. Do not
send default diff output. Do not make the diff from the new file to
the original file. Remember that any patch must not break other
systems. Remember that BFD must support cross compilation from any
host to any target, so patches which use ``#ifdef HOST'' are not
acceptable. Please also read the ``Reporting Bugs'' section of the
gcc manual.
Bug reports without patches will be remembered, but they may never get
fixed until somebody volunteers to fix them.
Copyright (C) 2012-2025 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.
0d6c6345b7