* [PATCH 4.4 28/30] MIPS: Fix bnezc/jialc return address calculation
[not found] <20170619152033.211450261@linuxfoundation.org>
@ 2017-06-19 15:21 ` Greg Kroah-Hartman
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From: Greg Kroah-Hartman @ 2017-06-19 15:21 UTC (permalink / raw)
To: linux-kernel
Cc: Greg Kroah-Hartman, stable, Paul Burton, linux-mips, Ralf Baechle
4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Paul Burton <paul.burton@imgtec.com>
commit 1a73d9310e093fc3adffba4d0a67b9fab2ee3f63 upstream.
The code handling the pop76 opcode (ie. bnezc & jialc instructions) in
__compute_return_epc_for_insn() needs to set the value of $31 in the
jialc case, which is encoded with rs = 0. However its check to
differentiate bnezc (rs != 0) from jialc (rs = 0) was unfortunately
backwards, meaning that if we emulate a bnezc instruction we clobber $31
& if we emulate a jialc instruction it actually behaves like a jic
instruction.
Fix this by inverting the check of rs to match the way the instructions
are actually encoded.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Fixes: 28d6f93d201d ("MIPS: Emulate the new MIPS R6 BNEZC and JIALC instructions")
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16178/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/mips/kernel/branch.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/arch/mips/kernel/branch.c
+++ b/arch/mips/kernel/branch.c
@@ -816,8 +816,10 @@ int __compute_return_epc_for_insn(struct
break;
}
/* Compact branch: BNEZC || JIALC */
- if (insn.i_format.rs)
+ if (!insn.i_format.rs) {
+ /* JIALC: set $31/ra */
regs->regs[31] = epc + 4;
+ }
regs->cp0_epc += 8;
break;
#endif
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