This is a note to let you know that I've just added the patch titled arm64: perf: Report the PC value in REGS_ABI_32 mode to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: arm64-perf-report-the-pc-value-in-regs_abi_32-mode.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 8dfe804a4031ca6ba3a3efb2048534249b64f3a5 Mon Sep 17 00:00:00 2001 From: Jiping Ma <jiping.ma2@xxxxxxxxxxxxx> Date: Mon, 11 May 2020 10:52:07 +0800 Subject: arm64: perf: Report the PC value in REGS_ABI_32 mode From: Jiping Ma <jiping.ma2@xxxxxxxxxxxxx> commit 8dfe804a4031ca6ba3a3efb2048534249b64f3a5 upstream. A 32-bit perf querying the registers of a compat task using REGS_ABI_32 will receive zeroes from w15, when it expects to find the PC. Return the PC value for register dwarf register 15 when returning register values for a compat task to perf. Cc: <stable@xxxxxxxxxxxxxxx> Acked-by: Mark Rutland <mark.rutland@xxxxxxx> Signed-off-by: Jiping Ma <jiping.ma2@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/1589165527-188401-1-git-send-email-jiping.ma2@xxxxxxxxxxxxx [will: Shuffled code and added a comment] Signed-off-by: Will Deacon <will@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/arm64/kernel/perf_regs.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-) --- a/arch/arm64/kernel/perf_regs.c +++ b/arch/arm64/kernel/perf_regs.c @@ -13,15 +13,34 @@ u64 perf_reg_value(struct pt_regs *regs, return 0; /* - * Compat (i.e. 32 bit) mode: - * - PC has been set in the pt_regs struct in kernel_entry, - * - Handle SP and LR here. + * Our handling of compat tasks (PERF_SAMPLE_REGS_ABI_32) is weird, but + * we're stuck with it for ABI compatability reasons. + * + * For a 32-bit consumer inspecting a 32-bit task, then it will look at + * the first 16 registers (see arch/arm/include/uapi/asm/perf_regs.h). + * These correspond directly to a prefix of the registers saved in our + * 'struct pt_regs', with the exception of the PC, so we copy that down + * (x15 corresponds to SP_hyp in the architecture). + * + * So far, so good. + * + * The oddity arises when a 64-bit consumer looks at a 32-bit task and + * asks for registers beyond PERF_REG_ARM_MAX. In this case, we return + * SP_usr, LR_usr and PC in the positions where the AArch64 SP, LR and + * PC registers would normally live. The initial idea was to allow a + * 64-bit unwinder to unwind a 32-bit task and, although it's not clear + * how well that works in practice, somebody might be relying on it. + * + * At the time we make a sample, we don't know whether the consumer is + * 32-bit or 64-bit, so we have to cater for both possibilities. */ if (compat_user_mode(regs)) { if ((u32)idx == PERF_REG_ARM64_SP) return regs->compat_sp; if ((u32)idx == PERF_REG_ARM64_LR) return regs->compat_lr; + if (idx == 15) + return regs->pc; } if ((u32)idx == PERF_REG_ARM64_SP) Patches currently in stable-queue which might be from jiping.ma2@xxxxxxxxxxxxx are queue-4.4/arm64-perf-report-the-pc-value-in-regs_abi_32-mode.patch