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[committed] MIPS: Rewrite `add_offset_16' to match its name
- From: "Maciej W. Rozycki" <macro at codesourcery dot com>
- To: <gdb-patches at sourceware dot org>
- Date: Sun, 5 Oct 2014 23:42:13 +0100
- Subject: [committed] MIPS: Rewrite `add_offset_16' to match its name
- Authentication-results: sourceware.org; auth=none
Hi,
We have a helper function called `add_offset_16' used by
`extended_mips16_next_pc' to calculate branch destinations. Weirdly
enough the helper does not do what the name suggests and rather than doing
its work for a 16-bit immediate branch offset it makes its calculations on
a 26-bit immediate target used by JAL and JALX instructions. Furthermore
the JAL/JALX calculation is only needed once by `extended_mips16_next_pc'
while a 16-bit branch offset calculation is made inline several times
across `extended_mips16_next_pc'.
This change therefore replaces the contents of `add_offset_16' with the
16-bit branch offset calculation and updates `extended_mips16_next_pc'
accordingly.
No regression across the usual mips-linux-gnu multilibs. Committed.
2014-10-05 Maciej W. Rozycki <macro@codesourcery.com>
gdb/
* mips-tdep.c (add_offset_16): Rewrite to implement what the
name implies.
(extended_mips16_next_pc): Update accordingly.
Maciej
gdb-mips16-jal-offset.diff
Index: gdb-fsf-trunk-quilt/gdb/mips-tdep.c
===================================================================
--- gdb-fsf-trunk-quilt.orig/gdb/mips-tdep.c 2014-10-03 20:24:53.000000000 +0100
+++ gdb-fsf-trunk-quilt/gdb/mips-tdep.c 2014-10-03 20:48:26.698978552 +0100
@@ -2178,10 +2178,13 @@ unpack_mips16 (struct gdbarch *gdbarch,
}
+/* Calculate the destination of a branch whose 16-bit opcode word is at PC,
+ and having a signed 16-bit OFFSET. */
+
static CORE_ADDR
add_offset_16 (CORE_ADDR pc, int offset)
{
- return ((offset << 2) | ((pc + 2) & (~(CORE_ADDR) 0x0fffffff)));
+ return pc + (offset << 1) + 2;
}
static CORE_ADDR
@@ -2196,7 +2199,7 @@ extended_mips16_next_pc (struct frame_in
{
struct upk_mips16 upk;
unpack_mips16 (gdbarch, pc, extension, insn, itype, &upk);
- pc += (upk.offset << 1) + 2;
+ pc = add_offset_16 (pc, upk.offset);
break;
}
case 3: /* JAL , JALX - Watch out, these are 32 bit
@@ -2204,7 +2207,7 @@ extended_mips16_next_pc (struct frame_in
{
struct upk_mips16 upk;
unpack_mips16 (gdbarch, pc, extension, insn, jalxtype, &upk);
- pc = add_offset_16 (pc, upk.offset);
+ pc = ((pc + 2) & (~(CORE_ADDR) 0x0fffffff)) | (upk.offset << 2);
if ((insn >> 10) & 0x01) /* Exchange mode */
pc = pc & ~0x01; /* Clear low bit, indicate 32 bit mode. */
else
@@ -2218,7 +2221,7 @@ extended_mips16_next_pc (struct frame_in
unpack_mips16 (gdbarch, pc, extension, insn, ritype, &upk);
reg = get_frame_register_signed (frame, mips_reg3_to_reg[upk.regx]);
if (reg == 0)
- pc += (upk.offset << 1) + 2;
+ pc = add_offset_16 (pc, upk.offset);
else
pc += 2;
break;
@@ -2230,7 +2233,7 @@ extended_mips16_next_pc (struct frame_in
unpack_mips16 (gdbarch, pc, extension, insn, ritype, &upk);
reg = get_frame_register_signed (frame, mips_reg3_to_reg[upk.regx]);
if (reg != 0)
- pc += (upk.offset << 1) + 2;
+ pc = add_offset_16 (pc, upk.offset);
else
pc += 2;
break;
@@ -2244,8 +2247,7 @@ extended_mips16_next_pc (struct frame_in
reg = get_frame_register_signed (frame, 24); /* Test register is 24 */
if (((upk.regx == 0) && (reg == 0)) /* BTEZ */
|| ((upk.regx == 1) && (reg != 0))) /* BTNEZ */
- /* pc = add_offset_16(pc,upk.offset) ; */
- pc += (upk.offset << 1) + 2;
+ pc = add_offset_16 (pc, upk.offset);
else
pc += 2;
break;