Re: [PATCH v3 1/2] fgraph: Enhance funcgraph-retval with BTF-based type-aware output

On Sun, Dec 14, 2025 at 9:15 AM kernel test robot [off-list ref] wrote:

Hi Donglin,

kernel test robot noticed the following build errors:

[auto build test ERROR on trace/for-next]
[also build test ERROR on linus/master v6.18 next-20251212]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Donglin-Peng/fgraph-Enhance-funcgraph-retval-with-BTF-based-type-aware-output/20251209-201633
base:   https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace for-next
patch link:    https://lore.kernel.org/r/20251209121349.525641-2-dolinux.peng%40gmail.com
patch subject: [PATCH v3 1/2] fgraph: Enhance funcgraph-retval with BTF-based type-aware output
config: arm-randconfig-002-20251214 (https://download.01.org/0day-ci/archive/20251214/202512140850.JdD1lPmn-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 10.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251214/202512140850.JdD1lPmn-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot [off-list ref]
| Closes: https://lore.kernel.org/oe-kbuild-all/202512140850.JdD1lPmn-lkp@intel.com/ (local)

All errors (new ones prefixed by >>):

   arm-linux-gnueabi-ld: kernel/trace/trace_functions_graph.o: in function `trim_retval':

quoted

quoted

kernel/trace/trace_functions_graph.c:888: undefined reference to `btf_find_func_proto'

Thanks. I will address this in the next version. The issue occurs because
CONFIG_FUNCTION_GRAPH_RETVAL and CONFIG_DEBUG_INFO_BTF
are enabled, but CONFIG_PROBE_EVENTS_BTF_ARGS is disabled.
This prevents trace_btf.c from being compiled, while the function
btf_find_func_proto
it provides is still required.

Thanks,
Donglin

vim +888 kernel/trace/trace_functions_graph.c

   872
   873  static void trim_retval(unsigned long func, unsigned long *retval, bool *print_retval,
   874                          int *fmt)
   875  {
   876          const struct btf_type *t;
   877          char name[KSYM_NAME_LEN];
   878          struct btf *btf;
   879          u32 v, msb;
   880          int kind;
   881
   882          if (!IS_ENABLED(CONFIG_DEBUG_INFO_BTF))
   883                  return;
   884
   885          if (lookup_symbol_name(func, name))
   886                  return;
   887
 > 888          t = btf_find_func_proto(name, &btf);
   889          if (IS_ERR_OR_NULL(t))
   890                  return;
   891
   892          t = btf_type_skip_modifiers(btf, t->type, NULL);
   893          kind = t ? BTF_INFO_KIND(t->info) : BTF_KIND_UNKN;
   894          switch (kind) {
   895          case BTF_KIND_UNKN:
   896                  *print_retval = false;
   897                  break;
   898          case BTF_KIND_STRUCT:
   899          case BTF_KIND_UNION:
   900          case BTF_KIND_ENUM:
   901          case BTF_KIND_ENUM64:
   902                  if (kind == BTF_KIND_STRUCT || kind == BTF_KIND_UNION)
   903                          *fmt = RETVAL_FMT_HEX;
   904                  else
   905                          *fmt = RETVAL_FMT_DEC;
   906
   907                  if (t->size > sizeof(unsigned long)) {
   908                          *fmt |= RETVAL_FMT_TRUNC;
   909                  } else {
   910                          msb = BITS_PER_BYTE * t->size - 1;
   911                          *retval &= GENMASK(msb, 0);
   912                  }
   913                  break;
   914          case BTF_KIND_INT:
   915                  v = *(u32 *)(t + 1);
   916                  if (BTF_INT_ENCODING(v) == BTF_INT_BOOL) {
   917                          *fmt = RETVAL_FMT_BOOL;
   918                          msb = 0;
   919                  } else {
   920                          if (BTF_INT_ENCODING(v) == BTF_INT_SIGNED)
   921                                  *fmt = RETVAL_FMT_DEC;
   922                          else
   923                                  *fmt = RETVAL_FMT_HEX;
   924
   925                          if (t->size > sizeof(unsigned long)) {
   926                                  *fmt |= RETVAL_FMT_TRUNC;
   927                                  msb = BITS_PER_LONG - 1;
   928                          } else {
   929                                  msb = BTF_INT_BITS(v) - 1;
   930                          }
   931                  }
   932                  *retval &= GENMASK(msb, 0);
   933                  break;
   934          default:
   935                  *fmt = RETVAL_FMT_HEX;
   936                  break;
   937          }
   938  }
   939

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