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* ia64-tdep.c: Update the comments on how we insert/remove

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breakpoints for L-X instructions.
        (ia64_memory_insert_breakpoint, ia64_memory_remove_breakpoint):
        Update the comments inside these functions.
This commit is contained in:
Joel Brobecker
2009-09-29 01:25:37 +00:00
parent 99e4058030
commit ca8b503212
2 changed files with 49 additions and 14 deletions
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7
gdb/ChangeLog
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@@ -1,3 +1,10 @@
2009-09-29 Joel Brobecker <brobecker@adacore.com>
* ia64-tdep.c: Update the comments on how we insert/remove
breakpoints for L-X instructions.
(ia64_memory_insert_breakpoint, ia64_memory_remove_breakpoint):
Update the comments inside these functions.
2009-09-28 Ulrich Weigand <uweigand@de.ibm.com>
* gdbarch.sh (displaced_step_hw_singlestep): New callback.

56
gdb/ia64-tdep.c
View File

@@ -586,6 +586,23 @@ fetch_instruction (CORE_ADDR addr, instruction_type *it, long long *instr)
SLOTNUM (`adress & 0x0f', value in the range <0..2>). We need to know
SLOTNUM in ia64_memory_remove_breakpoint.
There is one special case where we need to be extra careful:
L-X instructions, which are instructions that occupy 2 slots
(The L part is always in slot 1, and the X part is always in
slot 2). We must refuse to insert breakpoints for an address
that points at slot 2 of a bundle where an L-X instruction is
present, since there is logically no instruction at that address.
However, to make things more interesting, the opcode of L-X
instructions is located in slot 2. This means that, to insert
a breakpoint at an address that points to slot 1, we actually
need to write the breakpoint in slot 2! Slot 1 is actually
the extended operand, so writing the breakpoint there would not
have the desired effect. Another side-effect of this issue
is that we need to make sure that the shadow contents buffer
does save byte 15 of our instruction bundle (this is the tail
end of slot 2, which wouldn't be saved if we were to insert
the breakpoint in slot 1).
ia64 16-byte bundle layout:
| 5 bits | slot 0 with 41 bits | slot 1 with 41 bits | slot 2 with 41 bits |
@@ -594,12 +611,11 @@ fetch_instruction (CORE_ADDR addr, instruction_type *it, long long *instr)
== bp_tgt->shadow_len reqd \subset covered
0xABCDE0 0xABCDE0 0x10 <0x0...0x5> <0x0..0xF>
0xABCDE1 0xABCDE1 0xF <0x5...0xA> <0x1..0xF>
0xABCDE1 L-X 0xABCDE1 L-X 0xF <0xA...0xF> <0x1..0xF>
L is always in slot 1 and X is always in slot 2, while the address is
using slot 1 the breakpoint instruction must be placed
to the slot 2 (requiring to shadow that last byte at 0xF).
0xABCDE2 0xABCDE2 0xE <0xA...0xF> <0x2..0xF>
L-X instructions are treated a little specially, as explained above:
0xABCDE1 0xABCDE1 0xF <0xA...0xF> <0x1..0xF>
`objdump -d' and some other tools show a bit unjustified offsets:
original PC byte where starts the instruction objdump offset
0xABCDE0 0xABCDE0 0xABCDE0
@@ -643,19 +659,25 @@ ia64_memory_insert_breakpoint (struct gdbarch *gdbarch,
for addressing the SHADOW_CONTENTS placement. */
shadow_slotnum = slotnum;
/* Cover always the last byte of the bundle for the L-X slot case. */
/* Always cover the last byte of the bundle in case we are inserting
a breakpoint on an L-X instruction. */
bp_tgt->shadow_len = BUNDLE_LEN - shadow_slotnum;
/* Check for L type instruction in slot 1, if present then bump up the slot
number to the slot 2. */
template = extract_bit_field (bundle, 0, 5);
if (template_encoding_table[template][slotnum] == X)
{
/* X unit types can only be used in slot 2, and are actually
part of a 2-slot L-X instruction. We cannot break at this
address, as this is the second half of an instruction that
lives in slot 1 of that bundle. */
gdb_assert (slotnum == 2);
error (_("Can't insert breakpoint for non-existing slot X"));
}
if (template_encoding_table[template][slotnum] == L)
{
/* L unit types can only be used in slot 1. But the associated
opcode for that instruction is in slot 2, so bump the slot number
accordingly. */
gdb_assert (slotnum == 1);
slotnum = 2;
}
@@ -730,20 +752,26 @@ ia64_memory_remove_breakpoint (struct gdbarch *gdbarch,
for addressing the SHADOW_CONTENTS placement. */
shadow_slotnum = slotnum;
/* Check for L type instruction in slot 1, if present then bump up the slot
number to the slot 2. */
template = extract_bit_field (bundle_mem, 0, 5);
if (template_encoding_table[template][slotnum] == X)
{
/* X unit types can only be used in slot 2, and are actually
part of a 2-slot L-X instruction. We refuse to insert
breakpoints at this address, so there should be no reason
for us attempting to remove one there, except if the program's
code somehow got modified in memory. */
gdb_assert (slotnum == 2);
warning (_("Cannot remove breakpoint at address %s "
"from non-existing slot X, memory has changed underneath"),
warning (_("Cannot remove breakpoint at address %s from non-existing "
"X-type slot, memory has changed underneath"),
paddress (gdbarch, bp_tgt->placed_address));
do_cleanups (cleanup);
return -1;
}
if (template_encoding_table[template][slotnum] == L)
{
/* L unit types can only be used in slot 1. But the breakpoint
was actually saved using slot 2, so update the slot number
accordingly. */
gdb_assert (slotnum == 1);
slotnum = 2;
}
@@ -768,8 +796,8 @@ ia64_memory_remove_breakpoint (struct gdbarch *gdbarch,
bp_tgt->shadow_len);
instr_saved = slotN_contents (bundle_saved, slotnum);
/* In BUNDLE_MEM be careful to modify only the bits belonging to SLOTNUM and
never any other possibly also stored in SHADOW_CONTENTS. */
/* In BUNDLE_MEM, be careful to modify only the bits belonging to SLOTNUM
and not any of the other ones that are stored in SHADOW_CONTENTS. */
replace_slotN_contents (bundle_mem, instr_saved, slotnum);
val = target_write_memory (addr, bundle_mem, BUNDLE_LEN);