binutils-gdb

History

Nick Alcock 211bcd0133 bfd, ld, libctf: skip zero-refcount strings in CTF string reporting This is a tricky one. BFD, on the linker's behalf, reports symbols to libctf via the ctf_new_symbol and ctf_new_dynsym callbacks, which ultimately call ctf_link_add_linker_symbol. But while this happens after strtab offsets are finalized, it happens before the .dynstr is actually laid out, so we can't iterate over it at this stage and it is not clear what the reported symbols are actually called. So a second callback, examine_strtab, is called after the .dynstr is finalized, which calls ctf_link_add_strtab and ultimately leads to ldelf_ctf_strtab_iter_cb being called back repeatedly until the offsets of every string in the .dynstr is passed to libctf. libctf can then use this to get symbol names out of the input (which usually stores symbol types in the form of a name -> type mapping at this stage) and extract the types of those symbols, feeding them back into their final form as a 1:1 association with the real symtab's STT_OBJ and STT_FUNC symbols (with a few skipped, see ctf_symtab_skippable). This representation is compact, but has one problem: if libctf somehow gets confused about the st_type of a symbol, it'll stick an entry into the function symtypetab when it should put it into the object symtypetab, or vice versa, and every symbol from that one on will have the wrong CTF type because it's actually looking up the type for a different symbol. And we have just such a bug. ctf_link_add_strtab was not taking the refcounts of strings into consideration, so even strings that had been eliminated from the strtab by virtue of being in objects eliminated via --as-needed etc were being reported. This is harmful because it can lead to multiple strings with the same apparent offset, and if the last duplicate to be reported relates to an eliminated symbol, we look up the wrong symbol from the input and gets its type wrong: if it's unlucky and the eliminated symbol is also of the wrong st_type, we will end up with a corrupted symtypetab. Thankfully the wrong-st_type case is already diagnosed by a this-can-never-happen paranoid warning: CTF warning: Symbol 61a added to CTF as a function but is of type 1 or the converse * CTF warning: Symbol a3 added to CTF as a data object but is of type 2 so at least we can tell when the corruption has spread to more than one symbol's type. Skipping zero-refcounted strings is easy: teach _bfd_elf_strtab_str to skip them, and ldelf_ctf_strtab_iter_cb to loop over skipped strings until it falls off the end or finds one that isn't skipped. bfd/ChangeLog 2021-03-02 Nick Alcock <nick.alcock@oracle.com> * elf-strtab.c (_bfd_elf_strtab_str): Skip strings with zero refcount. ld/ChangeLog 2021-03-02 Nick Alcock <nick.alcock@oracle.com> * ldelfgen.c (ldelf_ctf_strtab_iter_cb): Skip zero-refcount strings. libctf/ChangeLog 2021-03-02 Nick Alcock <nick.alcock@oracle.com> * ctf-create.c (symtypetab_density): Report the symbol name as well as index in the name != object error; note the likely consequences. * ctf-link.c (ctf_link_shuffle_syms): Report the symbol index as well as name.		6 years ago
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testsuite	libctf, include: find types of symbols by name	6 years ago
.gitignore	libctf: restructure error handling to reduce relocations	6 years ago
ChangeLog	bfd, ld, libctf: skip zero-refcount strings in CTF string reporting	6 years ago
ChangeLog-2020	libctf: fix old ChangeLog typo	6 years ago
Makefile.am	libctf: require a Tcl capable of try/catch to run tests	6 years ago
Makefile.in	libctf regen for NEWS	6 years ago
NEWS	libctf: add a NEWS	6 years ago
aclocal.m4	Implement a workaround for GNU mak jobserver	6 years ago
config.h.in	libctf, dedup: add deduplicator	6 years ago
configure	libctf AC_CANONICAL_TARGET	6 years ago
configure.ac	libctf AC_CANONICAL_TARGET	6 years ago
ctf-archive.c	libctf: reimplement many _iter iterators in terms of _next	6 years ago
ctf-create.c	bfd, ld, libctf: skip zero-refcount strings in CTF string reporting	6 years ago
ctf-decl.c	libctf, ld: dump enums: generally improve dump formatting	6 years ago
ctf-decls.h	Update year range in copyright notice of binutils files	6 years ago
ctf-dedup.c	libctf: minor error-handling fixes	6 years ago
ctf-dump.c	libctf: fix signed/unsigned comparison confusion	6 years ago
ctf-endian.h	Update year range in copyright notice of binutils files	6 years ago
ctf-error.c	Update year range in copyright notice of binutils files	6 years ago
ctf-hash.c	Update year range in copyright notice of binutils files	6 years ago
ctf-impl.h	libctf: add a deduplicator-specific type mapping table	6 years ago
ctf-inlines.h	Update year range in copyright notice of binutils files	6 years ago
ctf-intl.h	Update year range in copyright notice of binutils files	6 years ago
ctf-labels.c	Update year range in copyright notice of binutils files	6 years ago
ctf-link.c	bfd, ld, libctf: skip zero-refcount strings in CTF string reporting	6 years ago
ctf-lookup.c	libctf, include: find types of symbols by name	6 years ago
ctf-open-bfd.c	Update year range in copyright notice of binutils files	6 years ago
ctf-open.c	libctf, include: find types of symbols by name	6 years ago
ctf-qsort_r.c	Update year range in copyright notice of binutils files	6 years ago
ctf-sha1.c	Update year range in copyright notice of binutils files	6 years ago
ctf-sha1.h	Update year range in copyright notice of binutils files	6 years ago
ctf-string.c	libctf: always name nameless types "", never NULL	6 years ago
ctf-subr.c	Update year range in copyright notice of binutils files	6 years ago
ctf-types.c	libctf: reimplement many _iter iterators in terms of _next	6 years ago
ctf-util.c	libctf, include: support unnamed structure members better	6 years ago
elf.h	Update year range in copyright notice of binutils files	6 years ago
libctf.ver	libctf, include: find types of symbols by name	6 years ago
swap.h	Update year range in copyright notice of binutils files	6 years ago