From 9ab4471c9f1b3e986f4d429951492f736c888ff6 Mon Sep 17 00:00:00 2001 From: "Maciej W. Rozycki" Date: Fri, 3 Apr 2015 23:26:56 +0100 Subject: [PATCH] MIPS: math-emu: Correct delay-slot exception propagation Restore EPC at the branch whose delay slot is emulated if the delay-slot instruction signals. This is so that code in `fpu_emulator_cop1Handler' does not see EPC having advanced and mistakenly successfully resume userland execution from the location at the branch target in that case. Restoring EPC guarantees an immediate exit from the emulation loop and if EPC hasn't advanced at all since entering the loop, also issuing the signal reported by the delay-slot instruction. Signed-off-by: Maciej W. Rozycki Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/9701/ Signed-off-by: Ralf Baechle --- arch/mips/math-emu/cp1emu.c | 34 +++++++++++++++++++++++++++++----- arch/mips/math-emu/dsemul.c | 2 +- 2 files changed, 30 insertions(+), 6 deletions(-) diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c index 732c3a37d7b9..acfef06b8311 100644 --- a/arch/mips/math-emu/cp1emu.c +++ b/arch/mips/math-emu/cp1emu.c @@ -1134,6 +1134,14 @@ emul: /* * Branch taken: emulate dslot instruction */ + unsigned long bcpc; + + /* + * Remember EPC at the branch to point back + * at so that any delay-slot instruction + * signal is not silently ignored. + */ + bcpc = xcp->cp0_epc; xcp->cp0_epc += dec_insn.pc_inc; contpc = MIPSInst_SIMM(ir); @@ -1159,7 +1167,15 @@ emul: * Single step the non-CP1 * instruction in the dslot. */ - return mips_dsemul(xcp, ir, contpc); + sig = mips_dsemul(xcp, ir, + contpc); + if (sig) + xcp->cp0_epc = bcpc; + /* + * SIGILL forces out of + * the emulation loop. + */ + return sig ? sig : SIGILL; } } else contpc = (xcp->cp0_epc + (contpc << 2)); @@ -1174,7 +1190,7 @@ emul: if (cpu_has_mips_2_3_4_5_r) goto emul; - return SIGILL; + goto bc_sigill; case cop1_op: goto emul; @@ -1184,7 +1200,7 @@ emul: /* its one of ours */ goto emul; - return SIGILL; + goto bc_sigill; case spec_op: switch (MIPSInst_FUNC(ir)) { @@ -1192,16 +1208,24 @@ emul: if (cpu_has_mips_4_5_r) goto emul; - return SIGILL; + goto bc_sigill; } break; + + bc_sigill: + xcp->cp0_epc = bcpc; + return SIGILL; } /* * Single step the non-cp1 * instruction in the dslot */ - return mips_dsemul(xcp, ir, contpc); + sig = mips_dsemul(xcp, ir, contpc); + if (sig) + xcp->cp0_epc = bcpc; + /* SIGILL forces out of the emulation loop. */ + return sig ? sig : SIGILL; } else if (likely) { /* branch not taken */ /* * branch likely nullifies diff --git a/arch/mips/math-emu/dsemul.c b/arch/mips/math-emu/dsemul.c index 00ad7365e453..e0b5cc27d78b 100644 --- a/arch/mips/math-emu/dsemul.c +++ b/arch/mips/math-emu/dsemul.c @@ -96,7 +96,7 @@ int mips_dsemul(struct pt_regs *regs, mips_instruction ir, unsigned long cpc) flush_cache_sigtramp((unsigned long)&fr->emul); - return SIGILL; /* force out of emulation loop */ + return 0; } int do_dsemulret(struct pt_regs *xcp) -- 2.20.1