Re: FAILED unresolved symbol vfs_truncate on arm64 with LLVM

On Fri, Feb 12, 2021 at 11:22:41AM -0800, Andrii Nakryiko wrote:

SNIP

quoted

+static int is_ftrace_func(struct elf_function *func, __u64 *addrs,
+                         __u64 count, bool kmod)
+{
+       /*
+        * For vmlinux image both addrs[x] and functions[x]::addr
+        * values are final address and are comparable.
+        *
+        * For kernel module addrs[x] is final address, but
+        * functions[x]::addr is relative address within section
+        * and needs to be relocated by adding sh_addr.
+        */
+       __u64 start = kmod ? func->addr + func->sh_addr : func->addr;
+       __u64 addr, end = func->addr + func->size;
+
+       /*
+        * The invariant here is addr[r] that is the smallest address
+        * that is >= than function start addr. Except the corner case
+        * where there is no such r, but for that we have a final check
+        * in the return.
+        */
+       size_t l = 0, r = count - 1, m;
+
+       /* make sure we don't use invalid r */
+       if (count == 0)
+               return false;
+
+       while (l < r) {
+               m = l + (r - l) / 2;
+               addr = addrs[m];
+
+               if (addr >= start) {
+                       /* we satisfy invariant, so tighten r */
+                       r = m;
+               } else {
+                       /* m is not good enough as l, maybe m + 1 will be */
+                       l = m + 1;
+               }
+       }
+
+       return start <= addrs[r] && addrs[r] < end;
+}
+
 static int setup_functions(struct btf_elf *btfe, struct funcs_layout *fl)
 {
        __u64 *addrs, count, i;

@@ -267,7 +321,7 @@ static int setup_functions(struct btf_elf *btfe, struct funcs_layout *fl)
        }

        qsort(addrs, count, sizeof(addrs[0]), addrs_cmp);
-       qsort(functions, functions_cnt, sizeof(functions[0]), functions_cmp);
+       qsort(functions, functions_cnt, sizeof(functions[0]), functions_cmp_addr);

All looks good except this. We don't rely on functions being sorted in
ascending start addr order, do we? If not, just drop this, no need to
slow down the process.

right, it's not needed when we use st_size for function size

thanks,
jirka