Hi Lijiang,
On Mon, Aug 29, 2022 at 8:36 PM lijiang <lijiang@xxxxxxxxxx> wrote:
>
> Hi, Tao
> Thank you for the patch.
> On Wed, Aug 24, 2022 at 12:12 PM <crash-utility-request@xxxxxxxxxx> wrote:
>>
>>
>> Date: Wed, 24 Aug 2022 12:10:33 +0800
>> From: Tao Liu <ltao@xxxxxxxxxx>
>> To: crash-utility@xxxxxxxxxx
>> Subject: [PATCH 1/2] Let gdb get kernel module symbols
>> info from crash
>> Message-ID: <20220824041033.40559-1-ltao@xxxxxxxxxx>
>> 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@xxxxxxxxxx>
>> ---
>> defs.h | 2 ++
>> gdb-10.2.patch | 35 +++++++++++++++++++++++++++++++++--
>> gdb_interface.c | 12 ++++++++++++
>> 3 files changed, 47 insertions(+), 2 deletions(-)
>>
>> 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..d08e9ab 100644
>> --- a/gdb-10.2.patch
>> +++ b/gdb-10.2.patch
>> @@ -399,7 +399,38 @@ exit 0
>> if (build_address_symbolic (gdbarch, addr, do_demangle, false, &name,
>> &offset, &filename, &line, &unmapped))
>> return 0;
>> -@@ -1221,6 +1230,43 @@ print_command_1 (const char *args, int voidprint)
>> +@@ -567,6 +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 */
>> +@@ -673,7 +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. */
>> +
>> +@@ -1221,6 +1246,43 @@ print_command_1 (const char *args, int voidprint)
>> print_value (val, print_opts);
>> }
>>
>
> Usually, the gdb patch needs to be put at the end of gdb-10.2.patch, which can help to
> apply your patch correctly. Could you please refer to the following commit?
> 4c85e982d25a ("gdb: fix for assigning NULL to std::string")
>
OK, it looks better, will update the v2 patch.
> In some commands, crash will trigger symbols loading via the value_search(), and also decide if the module symbols need to be loaded there, but for this case, there seems to be no better solution.
>
Yes.
Thanks,
Tao Liu
> Thanks.
> Lianbo
>
>> @@ -443,7 +474,7 @@ exit 0
>> /* See valprint.h. */
>>
>> void
>> -@@ -2855,6 +2901,12 @@ but no count or size letter (see \"x\" command)."),
>> +@@ -2855,6 +2917,12 @@ but no count or size letter (see \"x\" command)."),
>> c = add_com ("print", class_vars, print_command, print_help.c_str ());
>> set_cmd_completer_handle_brkchars (c, print_command_completer);
>> add_com_alias ("p", "print", class_vars, 1);
>> 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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