On 2022/08/29 22:45, Tao Liu wrote:
> 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.
Nice enhancement.
It would be helpful if you cannot do "mod -S" by some reason.
>
> 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
This is the second patch for gdb/printcmd.c, please add this,
just in case:
--- 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
Thanks,
Kazu
> +@@ -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.
> */
--
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