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sim/aarch64: Fix register ordering bug in blr (PR sim/25318) 

A comment in the implementation of blr says:

  /* The pseudo code in the spec says we update LR before fetching.
     the value from the rn.  */

With 'rn' being the register holding the destination address.

This may have been true at one point, but the ISA manual now clearly
shows the destination register being read before the link register is
written.

This commit updates the implementation of blr to match.

sim/aarch64/ChangeLog:

	PR sim/25318
	* simulator.c (blr): Read destination register before calling
	aarch64_save_LR.

Change-Id: Icb1c556064e3d9c807ac28440475caa205ab1064
This commit is contained in:
Carlo Bramini 2020-02-06 22:50:26 +00:00 committed by Andrew Burgess
parent 1d5d29e73f
commit 69b1ffdb01
2 changed files with 9 additions and 4 deletions
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6
sim/aarch64/ChangeLog
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@ -1,3 +1,9 @@
2020-02-06 Carlo Bramini <carlo_bramini@users.sourceforge.net>
PR sim/25318
* simulator.c (blr): Read destination register before calling
aarch64_save_LR.
2019-03-28 Andrew Burgess <andrew.burgess@embecosm.com>
* cpustate.c: Add 'libiberty.h' include.

7
sim/aarch64/simulator.c
View File

@ -13437,13 +13437,12 @@ br (sim_cpu *cpu)
static void
blr (sim_cpu *cpu)
{
unsigned rn = INSTR (9, 5);
/* Ensure we read the destination before we write LR. */
uint64_t target = aarch64_get_reg_u64 (cpu, INSTR (9, 5), NO_SP);
TRACE_DECODE (cpu, "emulated at line %d", __LINE__);
/* The pseudo code in the spec says we update LR before fetching.
the value from the rn. */
aarch64_save_LR (cpu);
aarch64_set_next_PC (cpu, aarch64_get_reg_u64 (cpu, rn, NO_SP));
aarch64_set_next_PC (cpu, target);
if (TRACE_BRANCH_P (cpu))
{