Hi Tao,
thank you for the patches.
On 2023/11/02 21:09, Tao Liu wrote:
> The address range may overlap for kernel modules global block vector,
> for example:
>
> module compunit_symtab block start block end
> floppy floppy.c ffffffffc0092000 ffffffffc00a4fa6
> virtio_blk virtio_blk.c ffffffffc00a4000 ffffffffc00fd080
hmm, this condition looks strange in the first place, is it inevitable?
In other words, I wonder if there might be something wrong with how to
load module symbol files.
What is the kernel version?
Do you have any patch to debug the gdb internal information?
I'd like to check vmcores on hand..
Thanks,
Kazu
>
> According to the gdb source code, the distance(block end - block start) of
> floppy(0x12fa6) is smaller than virtio_blk(0x59080), so address
> 0xffffffffc00a45b0, 0xffffffffc00a4370, 0xffffffffc00a4260 are translated
> by floppy module instead of virtio_blk module. However according
> to crash, the address range for the 2 modules are:
>
> crash> sym -l
> ffffffffc0092000 MODULE START: floppy
> ...snip...
> ffffffffc00a2f29 MODULE END: floppy
> ffffffffc00a4000 MODULE START: virtio_blk
> ...snip...
> ffffffffc00a86ec MODULE END: virtio_blk
>
> So the block vector address arrange and distance is not a reliable way to
> determine the symbol belonging of a specific kernel module. This patch will
> let gdb to query the module address range from crash, in order to locate the
> symbol belongings more percisely.
>
> Without the patch:
> crash> mod -S
> crash> struct blk_mq_ops 0xffffffffc00a7160
> struct blk_mq_ops {
> queue_rq = 0xffffffffc00a45b0 <floppy_module_init+1151>, <-- symbol translated from module floppy
> map_queue = 0xffffffff813015c0 <blk_mq_map_queue>,
> ...snip...
> complete = 0xffffffffc00a4370 <floppy_module_init+575>,
> init_request = 0xffffffffc00a4260 <floppy_module_init+303>,
> ...snip...
> }
>
> With the patch:
> crash> mod -S
> crash> struct blk_mq_ops 0xffffffffc00a7160
> struct blk_mq_ops {
> queue_rq = 0xffffffffc00a45b0 <virtio_queue_rq>, <-- symbol translated from module virtio_blk
> map_queue = 0xffffffff813015c0 <blk_mq_map_queue>,
> ...snip...
> complete = 0xffffffffc00a4370 <virtblk_request_done>,
> init_request = 0xffffffffc00a4260 <virtblk_init_request>,
> ...snip...
> }
>
> Signed-off-by: Tao Liu <ltao@xxxxxxxxxx>
> ---
> defs.h | 2 ++
> gdb-10.2.patch | 37 ++++++++++++++++++++++++++++++++++++-
> gdb_interface.c | 18 ++++++++++++++++++
> 3 files changed, 56 insertions(+), 1 deletion(-)
>
> diff --git a/defs.h b/defs.h
> index 788f63a..09e6738 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -5130,6 +5130,7 @@ 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 *);
> +ulong gdb_get_module_boundary(const char *, bool);
> extern "C" int same_file(char *, char *);
> #endif
>
> @@ -7687,6 +7688,7 @@ 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 *);
> +ulong gdb_get_module_boundary(const char *, bool);
> 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 31135ca..a5c10d3 100644
> --- a/gdb-10.2.patch
> +++ b/gdb-10.2.patch
> @@ -3203,4 +3203,39 @@ exit 0
> +#endif
> for (compunit_symtab *cust : obj_file->compunits ())
> {
> - const struct block *b;
> \ No newline at end of file
> + const struct block *b;
> +--- gdb-10.2/gdb/symtab.c.orig
> ++++ gdb-10.2/gdb/symtab.c
> +@@ -2895,6 +2895,10 @@ iterate_over_symbols_terminated
> + return callback (&block_sym);
> + }
> +
> ++#ifdef CRASH_MERGE
> ++extern "C" ulong gdb_get_module_boundary(const char *, bool);
> ++#endif
> ++
> + /* Find the compunit symtab associated with PC and SECTION.
> + This will read in debug info as necessary. */
> +
> +@@ -2932,11 +2936,21 @@ find_pc_sect_compunit_symtab (CORE_ADDR pc, struct obj_section *section)
> + for (objfile *obj_file : current_program_space->objfiles ())
> + {
> + #ifdef CRASH_MERGE
> ++ size_t sep;
> + std::string objfile_name = objfile_filename(obj_file);
> ++ const char *mod_name;
> +
> + if (objfile_name.find(".ko") != std::string::npos) {
> + if (obj_file->sf && obj_file->compunit_symtabs == nullptr)
> + obj_file->sf->qf->expand_all_symtabs(obj_file);
> ++ sep = objfile_name.find_last_of("/");
> ++ objfile_name = objfile_name.substr(sep + 1, objfile_name.size() - sep - 1);
> ++ sep = objfile_name.find_first_of(".");
> ++ objfile_name = objfile_name.substr(0, sep);
> ++ mod_name = objfile_name.c_str();
> ++ if (pc < gdb_get_module_boundary(mod_name, true) ||
> ++ pc > gdb_get_module_boundary(mod_name, false))
> ++ continue;
> + }
> + #endif
> + for (compunit_symtab *cust : obj_file->compunits ())
> diff --git a/gdb_interface.c b/gdb_interface.c
> index b14319c..a58fd68 100644
> --- a/gdb_interface.c
> +++ b/gdb_interface.c
> @@ -947,6 +947,24 @@ gdb_lookup_module_symbol(ulong addr, ulong *offset)
> }
> }
>
> +ulong
> +gdb_get_module_boundary(const char *module, bool is_start)
> +{
> + char buf[256];
> + struct syment *sp;
> +
> + if (is_start) {
> + snprintf(buf, sizeof(buf), "_MODULE_START_%s", module);
> + } else {
> + snprintf(buf, sizeof(buf), "_MODULE_END_%s", module);
> + }
> + sp = symbol_search(buf);
> + if (sp)
> + return sp->value;
> + else
> + return is_start ? 0 : (ulong)(-1);
> +}
> +
> /*
> * Used by gdb_interface() to catch gdb-related errors, if desired.
> */
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