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objtool: Add a pass for generating __mcount_loc

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Add the --mcount option for generating __mcount_loc sections
needed for dynamic ftrace. Using this pass requires the kernel to
be compiled with -mfentry and CC_USING_NOP_MCOUNT to be defined
in Makefile.

Link: https://lore.kernel.org/lkml/20200625200235.GQ4781@hirez.programming.kicks-ass.net/
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
[Sami: rebased, dropped config changes, fixed to actually use --mcount,
       and wrote a commit message.]
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Peter Zijlstra
2020-08-06 15:14:09 -07:00
committed by Kees Cook
parent 2b86895205
commit 99d0021569
6 changed files with 88 additions and 2 deletions
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82
tools/objtool/check.c
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@@ -530,6 +530,65 @@ static int create_static_call_sections(struct objtool_file *file)
return 0;
}
static int create_mcount_loc_sections(struct objtool_file *file)
{
struct section *sec, *reloc_sec;
struct reloc *reloc;
unsigned long *loc;
struct instruction *insn;
int idx;
sec = find_section_by_name(file->elf, "__mcount_loc");
if (sec) {
INIT_LIST_HEAD(&file->mcount_loc_list);
WARN("file already has __mcount_loc section, skipping");
return 0;
}
if (list_empty(&file->mcount_loc_list))
return 0;
idx = 0;
list_for_each_entry(insn, &file->mcount_loc_list, mcount_loc_node)
idx++;
sec = elf_create_section(file->elf, "__mcount_loc", 0, sizeof(unsigned long), idx);
if (!sec)
return -1;
reloc_sec = elf_create_reloc_section(file->elf, sec, SHT_RELA);
if (!reloc_sec)
return -1;
idx = 0;
list_for_each_entry(insn, &file->mcount_loc_list, mcount_loc_node) {
loc = (unsigned long *)sec->data->d_buf + idx;
memset(loc, 0, sizeof(unsigned long));
reloc = malloc(sizeof(*reloc));
if (!reloc) {
perror("malloc");
return -1;
}
memset(reloc, 0, sizeof(*reloc));
reloc->sym = insn->sec->sym;
reloc->addend = insn->offset;
reloc->type = R_X86_64_64;
reloc->offset = idx * sizeof(unsigned long);
reloc->sec = reloc_sec;
elf_add_reloc(file->elf, reloc);
idx++;
}
if (elf_rebuild_reloc_section(file->elf, reloc_sec))
return -1;
return 0;
}
/*
* Warnings shouldn't be reported for ignored functions.
*/
@@ -956,6 +1015,22 @@ static int add_call_destinations(struct objtool_file *file)
insn->type = INSN_NOP;
}
if (mcount && !strcmp(insn->call_dest->name, "__fentry__")) {
if (reloc) {
reloc->type = R_NONE;
elf_write_reloc(file->elf, reloc);
}
elf_write_insn(file->elf, insn->sec,
insn->offset, insn->len,
arch_nop_insn(insn->len));
insn->type = INSN_NOP;
list_add_tail(&insn->mcount_loc_node,
&file->mcount_loc_list);
}
/*
* Whatever stack impact regular CALLs have, should be undone
* by the RETURN of the called function.
@@ -2927,6 +3002,13 @@ int check(struct objtool_file *file)
goto out;
warnings += ret;
if (mcount) {
ret = create_mcount_loc_sections(file);
if (ret < 0)
goto out;
warnings += ret;
}
out:
if (ret < 0) {
/*