[PATCH 3/4] dwfl_error: support error details

[Jonathan Lebon <jlebon at redhat dot com>]

We add a new internal function, __libdwfl_seterrno_details(), which
accepts not just the error number but also an additional message to
provide more details about the error.

We also introduce a new interface function, dwfl_errmsg_details(), which
can be used to access the details message.

This new details string is meant as a way to provide additional
dynamically generated feedback to the user.

Signed-off-by: Jonathan Lebon <jlebon@redhat.com>
---
 libdw/libdw.map      |  1 +
 libdwfl/dwfl_error.c | 27 +++++++++++++++++++++++++++
 libdwfl/libdwfl.h    |  3 +++
 libdwfl/libdwflP.h   |  2 ++
 4 files changed, 33 insertions(+)

diff --git a/libdw/libdw.map b/libdw/libdw.map
index 1d4cbb0..17c13ef 100644
--- a/libdw/libdw.map
+++ b/libdw/libdw.map
@@ -98,6 +98,7 @@ ELFUTILS_0.122 {
     dwfl_cumodule;
     dwfl_end;
     dwfl_errmsg;
+    dwfl_errmsg_details;
     dwfl_errno;
     dwfl_getdwarf;
     dwfl_getmodules;
diff --git a/libdwfl/dwfl_error.c b/libdwfl/dwfl_error.c
index 56ec2b0..15b2ab5 100644
--- a/libdwfl/dwfl_error.c
+++ b/libdwfl/dwfl_error.c
@@ -43,6 +43,9 @@
 /* The error number.  */
 static __thread int global_error;
 
+/* Dynamically alloc'ed string with any additional details for error.  */
+static __thread char* global_error_details = NULL;
+
 
 int
 dwfl_errno (void)
@@ -129,11 +132,28 @@ __libdwfl_canon_error (Dwfl_Error error)
   return canonicalize (error);
 }
 
+static void
+set_error_details(char* new_details)
+{
+  if (global_error_details != NULL)
+    free (global_error_details);
+  global_error_details = new_details;
+}
+
 void
 internal_function
 __libdwfl_seterrno (Dwfl_Error error)
 {
   global_error = canonicalize (error);
+  set_error_details(NULL);
+}
+
+void
+internal_function
+__libdwfl_seterrno_details (Dwfl_Error error, char* details)
+{
+  global_error = canonicalize (error);
+  set_error_details(details);
 }
 
 
@@ -170,3 +190,10 @@ dwfl_errmsg (error)
 			  ? error : DWFL_E_UNKNOWN_ERROR]]);
 }
 INTDEF (dwfl_errmsg)
+
+const char *
+dwfl_errmsg_details ()
+{
+  return global_error_details;
+}
+INTDEF (dwfl_errmsg_details)
diff --git a/libdwfl/libdwfl.h b/libdwfl/libdwfl.h
index 2bb4f45..ad7b40e 100644
--- a/libdwfl/libdwfl.h
+++ b/libdwfl/libdwfl.h
@@ -102,6 +102,9 @@ extern int dwfl_errno (void);
    string is returned.  */
 extern const char *dwfl_errmsg (int err);
 
+/* Return more details about the last error if available, or NULL otherwise.  */
+extern const char *dwfl_errmsg_details (void);
+
 
 /* Start reporting the current set of segments and modules to the library.
    All existing segments are wiped.  Existing modules are marked to be
diff --git a/libdwfl/libdwflP.h b/libdwfl/libdwflP.h
index 12ee116..17db534 100644
--- a/libdwfl/libdwflP.h
+++ b/libdwfl/libdwflP.h
@@ -103,6 +103,7 @@ typedef enum { DWFL_ERRORS DWFL_E_NUM } Dwfl_Error;
 
 extern int __libdwfl_canon_error (Dwfl_Error) internal_function;
 extern void __libdwfl_seterrno (Dwfl_Error) internal_function;
+extern void __libdwfl_seterrno_details (Dwfl_Error, char*) internal_function;
 
 struct Dwfl
 {
@@ -691,6 +692,7 @@ extern int dwfl_link_map_report (Dwfl *dwfl, const void *auxv, size_t auxv_size,
 /* Avoid PLT entries.  */
 INTDECL (dwfl_begin)
 INTDECL (dwfl_errmsg)
+INTDECL (dwfl_errmsg_details)
 INTDECL (dwfl_errno)
 INTDECL (dwfl_addrmodule)
 INTDECL (dwfl_addrsegment)
-- 
2.1.0