On Wed, 27 Apr 2022 15:01:21 +0530 "Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:
> In the absence of section symbols [1], objtool (today) and recordmcount > (with a subsequent patch) generate __mcount_loc relocation records with > weak symbols as the base. This works fine as long as those weak symbols > are not overridden, but if they are, these can result in duplicate > entries in the final vmlinux mcount location table. This will cause > ftrace to fail when trying to patch the same location twice. Fix this by > dropping duplicate locations during ftrace init. > > [1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d1bcae833b32f1 > > Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com> > --- > kernel/trace/ftrace.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index 4f1d2f5e726341..8bc4f282bb3ff4 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -6496,7 +6496,7 @@ static int ftrace_process_locs(struct module *mod, > struct dyn_ftrace *rec; > unsigned long count; > unsigned long *p; > - unsigned long addr; > + unsigned long addr, prev_addr = 0; > unsigned long flags = 0; /* Shut up gcc */ > int ret = -ENOMEM; > > @@ -6550,6 +6550,16 @@ static int ftrace_process_locs(struct module *mod, > while (p < end) { > unsigned long end_offset; > addr = ftrace_call_adjust(*p++); > + > + /* > + * Drop duplicate entries, which can happen when weak > + * functions are overridden, and __mcount_loc relocation > + * records were generated against function names due to > + * absence of non-weak section symbols > + */ > + if (addr == prev_addr) > + addr = 0; Please don't use the side effect of addr == 0 causing the loop to continue for this logic. The two are not related. Simply call continue. if (addr == prev_addr) continue; -- Steve > + > /* > * Some architecture linkers will pad between > * the different mcount_loc sections of different > @@ -6569,6 +6579,7 @@ static int ftrace_process_locs(struct module *mod, > > rec = &pg->records[pg->index++]; > rec->ip = addr; > + prev_addr = addr; > } > > /* We should have used all pages */
