Re: [PATCH] align break instruction address in kgdb_set_sw_break

Bob,

Does gdb actually place breakpoints in middle of an instruction? If gdb does 
ever ask for a non-aligned breakpoint, when the breakpoint occurs, it'll be 
on a different address, not the one which gdb asked. gdb won't know that the 
breakpoint has occured. Won't it treat it as a spurious trap?

Am I missing something? 

I believe kgdb stub should refuse a non-aligned breakpoint.
-Amit

On Friday 13 Jan 2006 5:45 am, Bob Picco wrote:
> The check in kgdb_set_sw_break for reading the breakpoint location isn't
> exactly correct for ia64.  My brain hurts each time I must remember the
> ia64 instructionset layout but some description is required here. For a
> breakpoint address gdb sends kgdb the instruction bundle address+slot as
> the target address. An ia64 instruction is in a 128 bit bundle. Each bundle
> has three instruction slots and is 16 bytes aligned.  There are 41 bits per
> instruction and a 5
> bit template to identify what execution unit is used for each instruction
> slot; (41*3+5 = 128). Unless the breakpoint is in slot zero, which would be
> just luck, then the address sent to kgdb won't start on a bundle 16 byte
> aligned address. We need to align the address correctly before checking
> whether the entire ia64 bundle can be read.
>
> To summarize bundle slot 1 and slot 2 result in one byte and two bytes
> respectively being examined beyond the target bundle which is incorrect.
> In 2.6.14 and before this worked because the ia64 arch specific code,
> kgdb_arch_set_breakpoint, uses the correct magic.
>
> My other arch machines are busy.  I need to reinstall my i386 machine and
> then will test. Should someone test this patch then please email me.
>
> bob
>
> Signed-off-by: Bob Picco <bob.picco@xxxxxx>
>
>  include/asm-ia64/kgdb.h |    1 +
>  include/linux/kgdb.h    |    4 ++++
>  kernel/kgdb.c           |    4 ++--
>  3 files changed, 7 insertions(+), 2 deletions(-)
>
> Index: linux-2.6.15-kgdb/include/asm-ia64/kgdb.h
> ===================================================================
> --- linux-2.6.15-kgdb.orig/include/asm-ia64/kgdb.h    2006-01-11
> 13:45:23.000000000 -0500 +++
> linux-2.6.15-kgdb/include/asm-ia64/kgdb.h     2006-01-11 17:33:43.000000000
> -0500 @@ -26,6 +26,7 @@
>  #define KGDBBREAKNUM         0x6665UL
>  #define BREAKPOINT()         asm volatile ("break.m 0x6665")
>  #define BREAK_INSTR_SIZE     16
> +#define BREAK_INSTR_ALIGN    (~0xfUL)
>  #define CACHE_FLUSH_IS_SAFE  1
>
>  struct pt_regs;
> Index: linux-2.6.15-kgdb/include/linux/kgdb.h
> ===================================================================
> --- linux-2.6.15-kgdb.orig/include/linux/kgdb.h       2006-01-11
> 13:45:23.000000000 -0500 +++
> linux-2.6.15-kgdb/include/linux/kgdb.h        2006-01-11 17:33:43.000000000 
> -0500
> @@ -46,6 +46,10 @@ extern atomic_t kgdb_sync_softlockup[NR_
>
>  extern struct task_struct *kgdb_usethread, *kgdb_contthread;
>
> +#ifndef BREAK_INSTR_ALIGN
> +#define BREAK_INSTR_ALIGN    (~0UL)
> +#endif
> +
>  enum kgdb_bptype {
>       bp_breakpoint = '0',
>       bp_hardware_breakpoint,
> Index: linux-2.6.15-kgdb/kernel/kgdb.c
> ===================================================================
> --- linux-2.6.15-kgdb.orig/kernel/kgdb.c      2006-01-11 13:45:23.000000000
> -0500 +++ linux-2.6.15-kgdb/kernel/kgdb.c     2006-01-11 17:34:35.000000000
> -0500 @@ -829,8 +829,8 @@ static int kgdb_set_sw_break(unsigned lo
>       int i, breakno = -1;
>       int error = 0;
>       char tmp_variable[BREAK_INSTR_SIZE];
> -     if ((error = kgdb_get_mem((char *)addr, tmp_variable,
> -                             BREAK_INSTR_SIZE)) < 0)
> +     if ((error = kgdb_get_mem((char *)(addr & BREAK_INSTR_ALIGN),
> +             tmp_variable, BREAK_INSTR_SIZE)) < 0)
>               return error;
>       for (i = 0; i < MAX_BREAKPOINTS; i++) {
>               if ((kgdb_break[i].state == bp_set) &&
>
>
>
> -------------------------------------------------------
> This SF.net email is sponsored by: Splunk Inc. Do you grep through log
> files for problems?  Stop!  Download the new AJAX search engine that makes
> searching your log files as easy as surfing the  web.  DOWNLOAD SPLUNK!
> http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click
> _______________________________________________
> Kgdb-bugreport mailing list
> Kgdb-bugreport@xxxxxxxxxxxxxxxxxxxxx
> https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport


-------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
for problems?  Stop!  Download the new AJAX search engine that makes
searching your log files as easy as surfing the  web.  DOWNLOAD SPLUNK!
http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click