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SubjectRe: [PATCH bpf-next 2/3] ftrace: Keep address offset in ftrace_lookup_symbols
On Fri, May 27, 2022 at 1:56 PM Jiri Olsa <jolsa@kernel.org> wrote:
>
> We want to store the resolved address on the same index as
> the symbol string, because that's the user (bpf kprobe link)
> code assumption.
>
> Also making sure we don't store duplicates that might be
> present in kallsyms.
>
> Fixes: bed0d9a50dac ("ftrace: Add ftrace_lookup_symbols function")
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> kernel/trace/ftrace.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 674add0aafb3..00d0ba6397ed 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -7984,15 +7984,23 @@ static int kallsyms_callback(void *data, const char *name,
> struct module *mod, unsigned long addr)
> {
> struct kallsyms_data *args = data;
> + const char **sym;
> + int idx;
>
> - if (!bsearch(&name, args->syms, args->cnt, sizeof(*args->syms), symbols_cmp))
> + sym = bsearch(&name, args->syms, args->cnt, sizeof(*args->syms), symbols_cmp);
> + if (!sym)
> + return 0;
> +
> + idx = sym - args->syms;
> + if (args->addrs[idx])

if we have duplicated symbols we won't increment args->found here,
right? So we won't stop early. But we also don't want to increment
args->found here because we use it to check that we don't have
duplicates (in addition to making sure we resolved all the unique
symbols), right?

So I wonder if in this situation should we return some error code to
signify that we encountered symbol duplicate?


> return 0;
>
> addr = ftrace_location(addr);
> if (!addr)
> return 0;
>
> - args->addrs[args->found++] = addr;
> + args->addrs[idx] = addr;
> + args->found++;
> return args->found == args->cnt ? 1 : 0;
> }
>
> @@ -8017,6 +8025,7 @@ int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *a
> struct kallsyms_data args;
> int err;
>
> + memset(addrs, 0x0, sizeof(*addrs) * cnt);
> args.addrs = addrs;
> args.syms = sorted_syms;
> args.cnt = cnt;
> --
> 2.35.3
>

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