[Crash-utility] [PATCH] GDB: fix the failure of 'set scope' command

[lijiang]

在 2021年04月01日 17:24, HAGIO KAZUHITO(萩尾　一仁) 写道:
> Hi Lianbo,
> 
> -----Original Message-----
>> Currently, some command such as 'sys' may cause subsequent 'set scope'
>> commands to fail because it may not find the correct symtab associated
>> with PC and SECTION in the find_pc_sect_symtab(), eventually, this will
>> cause the following failure:
> 
> I could also reproduce the issue and the patch tested ok.
> 
> BTW, do you know what part of the sys command causes this issue?

Good question, only the sys command can not cause this failure. QE tried to
reproduce it many times, and eventually found the following command series
can easily reproduce this issue.

> It looks like the "set scope st_create" command itself should do the same
> thing to gdb, I cannot see what changes the behavior from the commit message.
> 
The "set scope st_create" command will get the address of block containing the
specified PC value via calling the block_for_pc() as below:

gdb_set_crash_scope()->
gdb_command_funnel()->
gdb_set_crash_block()->
block_for_pc()->
block_for_pc_sect()->
blockvector_for_pc_sect()->
find_pc_sect_symtab()----------- The problem is here.

But actually, it doesn't get the expected address of block from the find_pc_sect_symtab(),
so we have to correct it, check whether there is an address mapping to the 'block' in
the symtab searching loop and the PC value is in the range. If the symtab associated with
the PC value is found, and then use it.

Thanks.
Lianbo

> Thanks,
> Kazu
> 
>>
>> crash> mod -S 3.10.0-957.el7.x86_64
>> crash> mod -s dm_service_time
>> crash> set scope st_create
>> set: gdb cannot find text block for address: st_create
>> crash> mod -d dm_service_time
>> crash> mod -sr dm_service_time
>> crash> set scope st_create
>> scope: ffffffffc044d270 (st_create)
>> crash> sys
>>       KERNEL: 3.10.0-957.el7.x86_64/vmlinux
>>     DUMPFILE: crash/vmcore  [PARTIAL DUMP]
>>         CPUS: 48
>>         DATE: Sat Aug  3 11:41:00 EDT 2019
>>       UPTIME: 1 days, 10:28:48
>> LOAD AVERAGE: 2.95, 1.02, 0.40
>>        TASKS: 1060
>>     NODENAME: iop053063.lss.emc.com
>>      RELEASE: 3.10.0-957.el7.x86_64
>>      VERSION: #1 SMP Thu Oct 4 20:48:51 UTC 2018
>>      MACHINE: x86_64  (2999 Mhz)
>>       MEMORY: 127.9 GB
>>        PANIC: "SysRq : Trigger a crash"
>> crash> set scope st_create
>> set: gdb cannot find text block for address: st_create
>>
>> To find the correct symtab, let's check whether there is an address
>> mapping to 'block' in the symtab searching loop and the PC is in the
>> range. If the symtab associated with PC is found, and then use it.
>>
>> Signed-off-by: Lianbo Jiang <lijiang at redhat.com>
>> ---
>>  gdb-7.6.patch | 38 +++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 37 insertions(+), 1 deletion(-)
>>
>> diff --git a/gdb-7.6.patch b/gdb-7.6.patch
>> index f64b55fe547a..90629889f8c4 100644
>> --- a/gdb-7.6.patch
>> +++ b/gdb-7.6.patch
>> @@ -2500,4 +2500,40 @@ diff -up gdb-7.6/opcodes/configure.orig gdb-7.6/opcodes/configure
>>  +struct target_desc *tdesc_aarch64;
>>   #include "features/aarch64.c"
>>   #include "features/aarch64-without-fpu.c"
>> - 
>> +
>> +--- gdb-7.6/gdb/symtab.c.orig
>> ++++ gdb-7.6/gdb/symtab.c
>> +@@ -2065,7 +2065,7 @@ find_pc_sect_symtab (CORE_ADDR pc, struct obj_section *section)
>> +   struct symtab *s = NULL;
>> +   struct symtab *best_s = NULL;
>> +   struct objfile *objfile;
>> +-  CORE_ADDR distance = 0;
>> ++  CORE_ADDR distance = 0, start, end;
>> +   struct minimal_symbol *msymbol;
>> +
>> +   /* If we know that this is not a text address, return failure.  This is
>> +@@ -2102,10 +2102,20 @@ find_pc_sect_symtab (CORE_ADDR pc, struct obj_section *section)
>> +     bv = BLOCKVECTOR (s);
>> +     b = BLOCKVECTOR_BLOCK (bv, GLOBAL_BLOCK);
>> +
>> +-    if (BLOCK_START (b) <= pc
>> +-	&& BLOCK_END (b) > pc
>> +-	&& (distance == 0
>> +-	    || BLOCK_END (b) - BLOCK_START (b) < distance))
>> ++    start = BLOCK_START (b);
>> ++    end = BLOCK_END (b);
>> ++
>> ++    /*
>> ++     * If we have an addrmap mapping code addresses to blocks, and pc
>> ++     * is in the range [start, end), let's use it.
>> ++     */
>> ++    if ((pc >= start && pc < end) && BLOCKVECTOR_MAP (bv)) {
>> ++        if (addrmap_find (BLOCKVECTOR_MAP (bv), pc))
>> ++            return s;
>> ++    }
>> ++
>> ++    if ((pc >= start && pc < end) && ((distance == 0)
>> ++                                   || (end - start < distance)))
>> +       {
>> + 	/* For an objfile that has its functions reordered,
>> + 	   find_pc_psymtab will find the proper partial symbol table
>> --
>> 2.17.1
>