Hi all,

The latest GNU assembler (binutils-2.36.1) is removing unused section symbols like Clang [1]. So linux-5.10.15 can't be built with binutils-2.36.1 now. It has been reported as https://bugzilla.kernel.org/show_bug.cgi?id=211693.

I can confirm this commit fixes the issue. It should be cherry-picked into stable branches, so the following stable releases will be able to built with latest GNU toolchain.

[1]: https://sourceware.org/pipermail/binutils/2020-December/114671.html

At last, happy new lunar year guys :).

On 2020-12-16 13:49 +0000, tip-bot2 for Josh Poimboeuf wrote:

The following commit has been merged into the objtool/urgent branch of tip:

Commit-ID:     44f6a7c0755d8dd453c70557e11687bb080a6f21 Gitweb:        https://git.kernel.org/tip/44f6a7c0755d8dd453c70557e11687bb080a6f21 Author:        Josh Poimboeuf jpoimboe@redhat.com AuthorDate:    Mon, 14 Dec 2020 16:04:20 -06:00 Committer:     Peter Zijlstra peterz@infradead.org CommitterDate: Wed, 16 Dec 2020 14:35:46 +01:00

objtool: Fix seg fault with Clang non-section symbols

The Clang assembler likes to strip section symbols, which means objtool can't reference some text code by its section.  This confuses objtool greatly, causing it to seg fault.

The fix is similar to what was done before, for ORC reloc generation:

e81e07244325 ("objtool: Support Clang non-section symbols in ORC generation")

Factor out that code into a common helper and use it for static call reloc generation as well.

Reported-by: Arnd Bergmann arnd@kernel.org Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Nick Desaulniers ndesaulniers@google.com Reviewed-by: Miroslav Benes mbenes@suse.cz Link: https://github.com/ClangBuiltLinux/linux/issues/1207 Link: https://lkml.kernel.org/r/ba6b6c0f0dd5acbba66e403955a967d9fdd1726a.160798345...

---

tools/objtool/check.c   | 11 +++++++++--  tools/objtool/elf.c     | 26 ++++++++++++++++++++++++++  tools/objtool/elf.h     |  2 ++  tools/objtool/orc_gen.c | 29 +++++------------------------  4 files changed, 42 insertions(+), 26 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c index c6ab445..5f8d3ee 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -467,13 +467,20 @@ static int create_static_call_sections(struct objtool_file *file)                   /* populate reloc for 'addr' */                 reloc = malloc(sizeof(*reloc));

if (!reloc) {                         perror("malloc");                         return -1;                 }                 memset(reloc, 0, sizeof(*reloc)); -               reloc->sym = insn->sec->sym; -               reloc->addend = insn->offset;

+               insn_to_reloc_sym_addend(insn->sec, insn->offset, reloc); +               if (!reloc->sym) { +                       WARN_FUNC("static call tramp: missing containing symbol", +                                 insn->sec, insn->offset); +                       return -1; +               }

reloc->type = R_X86_64_PC32;                 reloc->offset = idx * sizeof(struct static_call_site);                 reloc->sec = reloc_sec; diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index 4e1d746..be89c74 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -262,6 +262,32 @@ struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, uns         return find_reloc_by_dest_range(elf, sec, offset, 1);  }   +void insn_to_reloc_sym_addend(struct section *sec, unsigned long offset, +                             struct reloc *reloc) +{ +       if (sec->sym) { +               reloc->sym = sec->sym; +               reloc->addend = offset; +               return; +       }

+       /* +        * The Clang assembler strips section symbols, so we have to reference +        * the function symbol instead: +        */ +       reloc->sym = find_symbol_containing(sec, offset); +       if (!reloc->sym) { +               /* +                * Hack alert.  This happens when we need to reference the NOP +                * pad insn immediately after the function. +                */ +               reloc->sym = find_symbol_containing(sec, offset - 1); +       }

+       if (reloc->sym) +               reloc->addend = offset - reloc->sym->offset; +}

static int read_sections(struct elf *elf)  {         Elf_Scn *s = NULL; diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h index 807f8c6..e6890cc 100644 --- a/tools/objtool/elf.h +++ b/tools/objtool/elf.h @@ -140,6 +140,8 @@ struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, uns  struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,                                      unsigned long offset, unsigned int len);  struct symbol *find_func_containing(struct section *sec, unsigned long offset); +void insn_to_reloc_sym_addend(struct section *sec, unsigned long offset, +                             struct reloc *reloc);  int elf_rebuild_reloc_section(struct elf *elf, struct section *sec);    #define for_each_sec(file, sec)                                                \ diff --git a/tools/objtool/orc_gen.c b/tools/objtool/orc_gen.c index 235663b..9ce68b3 100644 --- a/tools/objtool/orc_gen.c +++ b/tools/objtool/orc_gen.c @@ -105,30 +105,11 @@ static int create_orc_entry(struct elf *elf, struct section *u_sec, struct secti         }         memset(reloc, 0, sizeof(*reloc));   -       if (insn_sec->sym) { -               reloc->sym = insn_sec->sym; -               reloc->addend = insn_off; -       } else { -               /* -                * The Clang assembler doesn't produce section symbols, so we -                * have to reference the function symbol instead: -                */ -               reloc->sym = find_symbol_containing(insn_sec, insn_off); -               if (!reloc->sym) { -                       /* -                        * Hack alert.  This happens when we need to reference -                        * the NOP pad insn immediately after the function. -                        */ -                       reloc->sym = find_symbol_containing(insn_sec, -                                                          insn_off - 1); -               } -               if (!reloc->sym) { -                       WARN("missing symbol for insn at offset 0x%lx\n", -                            insn_off); -                       return -1; -               }

-               reloc->addend = insn_off - reloc->sym->offset; +       insn_to_reloc_sym_addend(insn_sec, insn_off, reloc); +       if (!reloc->sym) { +               WARN("missing symbol for insn at offset 0x%lx", +                    insn_off); +               return -1;         }           reloc->type = R_X86_64_PC32;