From cc503abf4ba30ed34bbf18b3fd8eaa8046fae48b Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Fri, 28 Feb 2025 16:24:24 +0000 Subject: [PATCH] target/arm: Make dummy debug registers RAZ, not NOP In debug_helper.c we provide a few dummy versions of debug registers: * DBGVCR (AArch32 only): enable bits for vector-catch debug events * MDCCINT_EL1: interrupt enable bits for the DCC debug communications channel * DBGVCR32_EL2: the AArch64 accessor for the state in DBGVCR We implemented these only to stop Linux crashing on startup, but we chose to implement them as ARM_CP_NOP. This worked for Linux where it only cares about trying to write to these registers, but is very confusing behaviour for anything that wants to read the registers (perhaps for context state switches), because the destination register will be left with whatever random value it happened to have before the read. Model these registers instead as RAZ. Fixes: 5e8b12ffbb8c68 ("target-arm: Implement minimal DBGVCR, OSDLR_EL1, MDCCSR_EL0") Fixes: 5dbdc4342f479d ("target-arm: Implement dummy MDCCINT_EL1") Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2708 Signed-off-by: Peter Maydell Reviewed-by: Richard Henderson Message-id: 20250228162424.1917269-1-peter.maydell@linaro.org --- target/arm/debug_helper.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/target/arm/debug_helper.c b/target/arm/debug_helper.c index 36bffde74e..a9a619ba6b 100644 --- a/target/arm/debug_helper.c +++ b/target/arm/debug_helper.c @@ -1037,7 +1037,7 @@ static const ARMCPRegInfo debug_cp_reginfo[] = { { .name = "DBGVCR", .cp = 14, .opc1 = 0, .crn = 0, .crm = 7, .opc2 = 0, .access = PL1_RW, .accessfn = access_tda, - .type = ARM_CP_NOP }, + .type = ARM_CP_CONST, .resetvalue = 0 }, /* * Dummy MDCCINT_EL1, since we don't implement the Debug Communications * Channel but Linux may try to access this register. The 32-bit @@ -1046,7 +1046,7 @@ static const ARMCPRegInfo debug_cp_reginfo[] = { { .name = "MDCCINT_EL1", .state = ARM_CP_STATE_BOTH, .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 0, .crm = 2, .opc2 = 0, .access = PL1_RW, .accessfn = access_tdcc, - .type = ARM_CP_NOP }, + .type = ARM_CP_CONST, .resetvalue = 0 }, /* * Dummy DBGCLAIM registers. * "The architecture does not define any functionality for the CLAIM tag bits.", @@ -1075,7 +1075,8 @@ static const ARMCPRegInfo debug_aa32_el1_reginfo[] = { { .name = "DBGVCR32_EL2", .state = ARM_CP_STATE_AA64, .opc0 = 2, .opc1 = 4, .crn = 0, .crm = 7, .opc2 = 0, .access = PL2_RW, .accessfn = access_dbgvcr32, - .type = ARM_CP_NOP | ARM_CP_EL3_NO_EL2_KEEP }, + .type = ARM_CP_CONST | ARM_CP_EL3_NO_EL2_KEEP, + .resetvalue = 0 }, }; static const ARMCPRegInfo debug_lpae_cp_reginfo[] = { -- 2.39.5