[PATCH] fgraph: Format error pointers as signed errno values

[Donglin Peng <dolinux.peng@gmail.com>]

From: pengdonglin <pengdonglin@xiaomi.com>

The BTF-aware funcgraph-retval formatter currently treats all pointer
returns as hexadecimal values. Error pointers returned with ERR_PTR()
therefore appear as high unsigned addresses in smart mode, obscuring the
underlying errno.

Recognize error-pointer values for pointer return types in
btf_trim_retval() and select signed decimal formatting.

Before:
  trim_retval_ptr_error(); /* ret=0xffffffffffffffea */

After:
  trim_retval_ptr_error(); /* ret=-22 */

Users who need to inspect the raw encoded value can enable
funcgraph-retval-hex, which produces:

  trim_retval_ptr_error(); /* ret=0xffffffffffffffea */

Signed-off-by: pengdonglin <pengdonglin@xiaomi.com>
---
 kernel/trace/trace_btf.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/trace/trace_btf.c b/kernel/trace/trace_btf.c
index bcf65fec7bb1..1201105aa48b 100644
--- a/kernel/trace/trace_btf.c
+++ b/kernel/trace/trace_btf.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/btf.h>
+#include <linux/err.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/kallsyms.h>
@@ -197,6 +198,12 @@ void btf_trim_retval(unsigned long func, unsigned long *retval, bool *print_retv
 		if (signed_type && !hex)
 			*retval = sign_extend64(*retval, msb);
 		break;
+	case BTF_KIND_PTR:
+		if (!hex && IS_ERR_VALUE(*retval))
+			*fmt = RETVAL_FMT_DEC;
+		else
+			*fmt = RETVAL_FMT_HEX;
+		break;
 	default:
 		*fmt = RETVAL_FMT_HEX;
 		break;
-- 
2.34.1