Re: [RFA/commit/powerpc] breakpoint inserted past function end

[Michael Snyder <msnyder@vmware.com>]

This seems reasonable to me.

Joel Brobecker wrote:
> On powerpc, the prologue scanner reads instruction after instruction,
> and just skips instructions that do not affect a frame.  This means
> that it does not stop if if finds and unexpected instruction (which
> could possibly happen with optimization, I presume). To avoid scanning
> too many instructions, it tries to establish an upper limit.
> 
> The upper limit is first computed using the debugging (line) info,
> but if that fails, it falls back on an arbitrary 100 bytes (or 25
> instructions).  The problem is that, if the function is shorter than
> those 25 instructions, we run the risk of skipping the entire function
> and returning a PC that's outside our function.
> 
> In the event where we can find a symbol for a given PC (and therefore
> can determine function start and end addresses), but cannot find an
> upper limit using skip_prologue_using_sal, then we can at least limit
> make sure that the 25 instructions do not put us beyour our function.
> If it does, then further reduce the upper-limit to the end of the function.
> 
> gdb/ChangeLog:
> 
>         * rs6000-tdep.c (rs6000_skip_prologue): Make sure that the prologue
>         upper limit address is not greater than the function end address
>         when the upper limit could not be computed using the debugging
>         info.
> 
> This seems fairly straightforward, but I couldn't run the testsuite
> (only the AdaCore testsuite) because I don't have access to a powerpc
> machine running an OS that we can run the testsuite on (I ran the AdaCore
> testsuite on VxWorks).
> 
> I'll commit in a few days, pending comments.
> 
> ---
>  gdb/rs6000-tdep.c |    9 +++++++--
>  1 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
> index c16e933..9832b5b 100644
> --- a/gdb/rs6000-tdep.c
> +++ b/gdb/rs6000-tdep.c
> @@ -2090,12 +2090,12 @@ static CORE_ADDR
>  rs6000_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc)
>  {
>    struct rs6000_framedata frame;
> -  CORE_ADDR limit_pc, func_addr;
> +  CORE_ADDR limit_pc, func_addr, func_end_addr = 0;
>  
>    /* See if we can determine the end of the prologue via the symbol table.
>       If so, then return either PC, or the PC after the prologue, whichever
>       is greater.  */
> -  if (find_pc_partial_function (pc, NULL, &func_addr, NULL))
> +  if (find_pc_partial_function (pc, NULL, &func_addr, &func_end_addr))
>      {
>        CORE_ADDR post_prologue_pc
>  	= skip_prologue_using_sal (gdbarch, func_addr);
> @@ -2113,6 +2113,11 @@ rs6000_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc)
>    if (limit_pc == 0)
>      limit_pc = pc + 100;          /* Magic.  */
>  
> +  /* Do not allow limit_pc to be past the function end, if we know
> +     where that end is...  */
> +  if (func_end_addr && limit_pc > func_end_addr)
> +    limit_pc = func_end_addr;
> +
>    pc = skip_prologue (gdbarch, pc, limit_pc, &frame);
>    return pc;
>  }