yggdrasil/binutils-gdb
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Invalidate a register in cache when a remote target failed to write it.

Browse Source 
As shown by the bug report, GDB crashes when the remote target was unable to
write to a register (the program counter) with the 'P' packet. This was reported
for AVR but can be reproduced on any architecture with a gdbserver that fails to
handle a 'P' packet.

Issue
=====

This GDB session was done with a custom gdbserver patched to send an error
packet when trying to set the program counter with a 'P' packet:

~~~
(gdb) file Debug/ATMega2560-simple-program.elf
Reading symbols from Debug/ATMega2560-simple-program.elf...done.
(gdb) target remote :51000
Remote debugging using :51000
0x00000000 in __vectors ()
(gdb) load
Loading section .text, size 0x1fc lma 0x0
Start address 0x0, load size 508
Transfer rate: 248 KB/sec, 169 bytes/write.
(gdb) b main
Breakpoint 1 at 0x164: file .././ATMega2560-simple-program.c, line 39.
(gdb) c
Continuing.

Program received signal SIGTRAP, Trace/breakpoint trap.
main () at .././ATMega2560-simple-program.c:42
42		DDRD |= LED0_MASK;// | LED1_MASK;
(gdb) info line 43
Line 43 of ".././ATMega2560-simple-program.c" is at address 0x178 <main+40> but contains no code.
(gdb) set $pc=0x178
Could not write register "PC2"; remote failure reply 'E00'
(gdb) info registers pc
pc             0x178	0x178 <main+40>
(gdb) s
../../unisrc-mainline/gdb/infrun.c:1978: internal-error: resume: Assertion `pc_in_thread_step_range (pc, tp)' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n)
../../unisrc-mainline/gdb/infrun.c:1978: internal-error: resume: Assertion `pc_in_thread_step_range (pc, tp)' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Create a core file of GDB? (y or n)
~~~

We can see that even though GDB reports that writing to the register failed, the
register cache was updated:

~~~
(gdb) set $pc=0x178
Could not write register "PC2"; remote failure reply 'E00'
(gdb) info registers pc
pc             0x178	0x178 <main+40>
~~~

The root of the problem is of course in the gdbserver but I thought GDB should
keep a register cache consistent with the hardware even in case of a failure.

Changes
=======

This patch adds routines to add a regcache_invalidate cleanup to the current
chain.

We can then register one before calling target_store_registers. This way if the
target throws an error, the register we wanted to write to will be invalidated
in cache. If target_store_registers succeeds, we can discard the new cleanup.

2014-06-12  Pierre Langlois  <pierre.langlois@embecosm.com>

	* regcache.c (struct register_to_invalidate): New structure.
	(do_register_invalidate, make_cleanup_regcache_invalidate): New
	functions.
	(regcache_raw_write): Call make_cleanup_regcache_invalidate.
This commit is contained in:
Pierre Langlois 2014-05-20 15:13:20 +01:00
parent d495ab0d84
commit b94ade4284
2 changed files with 47 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
gdb/ChangeLog
View File

@ -1,3 +1,10 @@
2014-06-12 Pierre Langlois <pierre.langlois@embecosm.com>
* regcache.c (struct register_to_invalidate): New structure.
(do_register_invalidate, make_cleanup_regcache_invalidate): New
functions.
(regcache_raw_write): Call make_cleanup_regcache_invalidate.
2014-06-12 Yao Qi <yao@codesourcery.com>
* varobj.c (varobj_get_num_children): Call

43
gdb/regcache.c
View File

@ -267,6 +267,32 @@ make_cleanup_regcache_xfree (struct regcache *regcache)
return make_cleanup (do_regcache_xfree, regcache);
}
/* Cleanup routines for invalidating a register. */
struct register_to_invalidate
{
struct regcache *regcache;
int regnum;
};
static void
do_regcache_invalidate (void *data)
{
struct register_to_invalidate *reg = data;
regcache_invalidate (reg->regcache, reg->regnum);
}
static struct cleanup *
make_cleanup_regcache_invalidate (struct regcache *regcache, int regnum)
{
struct register_to_invalidate* reg = XNEW (struct register_to_invalidate);
reg->regcache = regcache;
reg->regnum = regnum;
return make_cleanup_dtor (do_regcache_invalidate, (void *) reg, xfree);
}
/* Return REGCACHE's architecture. */
struct gdbarch *
@ -846,7 +872,8 @@ void
regcache_raw_write (struct regcache *regcache, int regnum,
const gdb_byte *buf)
{
struct cleanup *old_chain;
struct cleanup *chain_before_save_inferior;
struct cleanup *chain_before_invalidate_register;
gdb_assert (regcache != NULL && buf != NULL);
gdb_assert (regnum >= 0 && regnum < regcache->descr->nr_raw_registers);
@ -864,16 +891,26 @@ regcache_raw_write (struct regcache *regcache, int regnum,
regcache->descr->sizeof_register[regnum]) == 0))
return;
old_chain = save_inferior_ptid ();
chain_before_save_inferior = save_inferior_ptid ();
inferior_ptid = regcache->ptid;
target_prepare_to_store (regcache);
memcpy (register_buffer (regcache, regnum), buf,
regcache->descr->sizeof_register[regnum]);
regcache->register_status[regnum] = REG_VALID;
/* Register a cleanup function for invalidating the register after it is
written, in case of a failure. */
chain_before_invalidate_register
= make_cleanup_regcache_invalidate (regcache, regnum);
target_store_registers (regcache, regnum);
do_cleanups (old_chain);
/* The target did not throw an error so we can discard invalidating the
register and restore the cleanup chain to what it was. */
discard_cleanups (chain_before_invalidate_register);
do_cleanups (chain_before_save_inferior);
}
void