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Re: [RFC] Calling mips-tdep.c:read_next_frame_reg with null frame?
- From: Andrew Cagney <cagney at gnu dot org>
- To: Joel Brobecker <brobecker at gnat dot com>
- Cc: gdb-patches at sources dot redhat dot com
- Date: Tue, 12 Oct 2004 17:26:13 -0400
- Subject: Re: [RFC] Calling mips-tdep.c:read_next_frame_reg with null frame?
- References: <20041011040934.GD26446@gnat.com>
I am wondering what would happen if we were to call mips32_scan_prologue
with a NULL frame, which I think is something that we are doing on a
regular basis. See for instance how after_prologue that calls
heuristic_proc_desc with a NULL frame, which gets passed to scan_prologue.
There is some code in that function that does:
frame_addr = read_next_frame_reg (next_frame, NUM_REGS + 30);
Looking at read_next_frame_reg():
static CORE_ADDR
read_next_frame_reg (struct frame_info *fi, int regno)
{
/* Always a pseudo. */
gdb_assert (regno >= NUM_REGS);
if (fi == NULL)
{
LONGEST val;
regcache_cooked_read_signed (current_regcache, regno, &val);
return val;
}
else
return frame_unwind_register_signed (fi, regno);
So when the frame is null, we fetch some value from the regcache.
But what if we don't have any inferior? Looks like we have to be
a bit careful with the following code:
else if (frame_reg == MIPS_SP_REGNUM)
{
unsigned alloca_adjust;
frame_reg = 30;
frame_addr = read_next_frame_reg (next_frame, NUM_REGS + 30);
alloca_adjust = (unsigned) (frame_addr - (sp + low_word));
if (alloca_adjust > 0)
{
/* FP > SP + frame_size. This may be because of
an alloca or somethings similar. Fix sp to
"pre-alloca" value, and try again. */
sp += alloca_adjust;
/* Need to reset the status of all registers. Otherwise,
we will hit a guard that prevents the new address
for each register to be recomputed during the second
pass. */
reset_saved_regs (this_cache);
goto restart;
}
}
Same for
/* move $30,$sp. With different versions of gas this will be either
`addu $30,$sp,$zero' or `or $30,$sp,$zero' or `daddu 30,sp,$0'.
Accept any one of these. */
else if (inst == 0x03A0F021 || inst == 0x03a0f025 || inst == 0x03a0f02d)
{
/* New gcc frame, virtual frame pointer is at r30 + frame_size. */
if (frame_reg == MIPS_SP_REGNUM)
{
unsigned alloca_adjust;
frame_reg = 30;
frame_addr = read_next_frame_reg (next_frame, NUM_REGS + 30);
(etc...)
I suggest modifying the (frame_reg == SP_REGNUM) check into
(frame_reg == SP_REGNUM && next_frame != NULL)
with a comment saying that if NEXT_FRAME is null, then we're probably
not analyzing a live frame, but just scanning the prologue. So we don't
need to do anything special for this instruction.
Yes (it's definitly not a live frame so the information extracted from
the instructions doesn't need to be saved). Btw, if you replace:
reset_saved_regs (this_cache);
goto restart;
with
reset_saved_regs (this_cache);
frame_offset = 0;
I believe that you can blow away the GOTO.
Andrew