Re: [PATCH bpf-next 2/3] ftrace: Keep address offset in ftrace_lookup_symbols
From: Andrii Nakryiko <hidden>
Date: 2022-06-02 22:52:25
Also in:
bpf, lkml
On Fri, May 27, 2022 at 1:56 PM Jiri Olsa [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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?
quoted hunk ↗ jump to hunk
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