[Crash-utility] [PATCH v3 1/2] Let gdb get kernel module symbols info from crash

[lijiang]

Hi, Tao
Thank you for the update.
On Wed, Aug 31, 2022 at 11:58 AM <crash-utility-request at redhat.com> wrote:

> Date: Wed, 31 Aug 2022 11:54:13 +0800
> From: Tao Liu <ltao at redhat.com>
> To: crash-utility at redhat.com
> Subject: [Crash-utility] [PATCH v3 1/2] Let gdb get kernel module
>         symbols info from crash
> Message-ID: <20220831035413.10831-1-ltao at redhat.com>
> Content-Type: text/plain; charset="US-ASCII"; x-default=true
>
> 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 at redhat.com>
> ---
> v1 -> v2: Append the modification hunk at the end of gdb-10.2.patch
> v2 -> v3: Add printcmd.c to "tar xvzmf"
>

 For the v3 patchset: Ack.

Thanks.
Lianbo

---
>  defs.h          |  2 ++
>  gdb-10.2.patch  | 35 +++++++++++++++++++++++++++++++++++
>  gdb_interface.c | 12 ++++++++++++
>  3 files changed, 49 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..642cd6a 100644
> --- a/gdb-10.2.patch
> +++ b/gdb-10.2.patch
> @@ -9,6 +9,7 @@
>  # to all subsequent patch applications.
>
>  tar xvzmf gdb-10.2.tar.gz \
> +       gdb-10.2/gdb/printcmd.c \
>         gdb-10.2/gdb/symfile.c \
>         gdb-10.2/gdb/Makefile.in
>
> @@ -1661,3 +1662,37 @@ 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
>
>
>
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