[PATCH v2 1/2] Let gdb get kernel module symbols info from crash

[Tao Liu <ltao@xxxxxxxxxx>]

Gdb will try to resolve an address to its corresponding symbol name such as
when printing a structure. It works fine for kernel symbols, because gdb can
find them through vmlinux. However as for kernel modules symbols, crash
resolves them by dig into "struct module", which gdb don't know. As a
results, gdb fails to translate an kernel modules address to it's symbolic
name. For example we can reproduce the issue as follows.

    crash> timer
    ....
    4331308176       336  ffff94ea24240860  ffffffffc03762c0  <estimation_timer>
    ....
    crash> sym 0xffffffffc03762c0
    ffffffffc03762c0 (t) estimation_timer [ip_vs]

Before patch:
    crash> timer_list ffff94ea24240860
    struct timer_list {
      ....
      function = 0xffffffffc03762c0,
      ....
    }

After patch:
    crash> timer_list ffff94ea24240860
    struct timer_list {
      ....
      function = 0xffffffffc03762c0 <estimation_timer>,
      ....
    }

In this patch, we add an interface for gdb, when gdb trying to build kernel
module's address symbolic, the info can be get from crash.

Signed-off-by: Tao Liu <ltao@xxxxxxxxxx>
---
v1 -> v2: Append the modification hunk at the end of gdb-10.2.patch 
---
 defs.h          |  2 ++
 gdb-10.2.patch  | 34 ++++++++++++++++++++++++++++++++++
 gdb_interface.c | 12 ++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/defs.h b/defs.h
index 9d6d891..afdcf6c 100644
--- a/defs.h
+++ b/defs.h
@@ -4874,6 +4874,7 @@ extern "C" int patch_kernel_symbol(struct gnu_request *);
 struct syment *symbol_search(char *);
 int gdb_line_number_callback(ulong, ulong, ulong);
 int gdb_print_callback(ulong);
+char *gdb_lookup_module_symbol(ulong, ulong *);
 extern "C" int same_file(char *, char *);
 #endif
 
@@ -7284,6 +7285,7 @@ int gdb_pass_through(char *, FILE *, ulong);
 int gdb_readmem_callback(ulong, void *, int, int);
 int gdb_line_number_callback(ulong, ulong, ulong);
 int gdb_print_callback(ulong);
+char *gdb_lookup_module_symbol(ulong, ulong *);
 void gdb_error_hook(void);
 void restore_gdb_sanity(void);
 int is_gdb_command(int, ulong);
diff --git a/gdb-10.2.patch b/gdb-10.2.patch
index f0034ed..4fe16b0 100644
--- a/gdb-10.2.patch
+++ b/gdb-10.2.patch
@@ -1661,3 +1661,37 @@ exit 0
 +       return name_copy ? std::string (name_copy) : std::string ();
    }
  #endif
+ 
+--- gdb-10.2/gdb/printcmd.c.orig
++++ gdb-10.2/gdb/printcmd.c
+@@ -576,6 +576,10 @@ print_address_symbolic (struct gdbarch *gdbarch, CORE_ADDR addr,
+ 
+ /* See valprint.h.  */
+ 
++#ifdef CRASH_MERGE
++extern "C" char *gdb_lookup_module_symbol(unsigned long, unsigned long *);
++#endif
++
+ int
+ build_address_symbolic (struct gdbarch *gdbarch,
+ 			CORE_ADDR addr,  /* IN */
+@@ -682,7 +686,19 @@ build_address_symbolic (struct gdbarch *gdbarch,
+ 	}
+     }
+   if (symbol == NULL && msymbol.minsym == NULL)
++#ifdef CRASH_MERGE
++  {
++    char *name_ptr = gdb_lookup_module_symbol(addr, (unsigned long *)offset);
++    if (name_ptr) {
++      *name = name_ptr;
++      return 0;
++    } else {
++      return 1;
++    }
++  }
++#else
+     return 1;
++#endif
+ 
+   /* If the nearest symbol is too far away, don't print anything symbolic.  */
+ 
diff --git a/gdb_interface.c b/gdb_interface.c
index 3a7fcc9..b14319c 100644
--- a/gdb_interface.c
+++ b/gdb_interface.c
@@ -935,6 +935,18 @@ gdb_print_callback(ulong addr)
 		return IS_KVADDR(addr);
 }
 
+char *
+gdb_lookup_module_symbol(ulong addr, ulong *offset)
+{
+	struct syment *sp;
+
+	if ((sp = value_search_module(addr, offset))) {
+		return sp->name;
+	} else {
+		return NULL;
+	}
+}
+
 /*
  *  Used by gdb_interface() to catch gdb-related errors, if desired.
  */
-- 
2.33.1

--
Crash-utility mailing list
Crash-utility@xxxxxxxxxx
https://listman.redhat.com/mailman/listinfo/crash-utility
Contribution Guidelines: https://github.com/crash-utility/crash/wiki