Re: [Crash-utility] [PATCH v2 1/2] Let gdb get kernel module symbols info from crash

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(a)redhat.com&gt; > --- > 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. > */