Commit 8dfe804a authored by Jiping Ma's avatar Jiping Ma Committed by Will Deacon
Browse files

arm64: perf: Report the PC value in REGS_ABI_32 mode



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@vger.kernel.org>
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarJiping Ma <jiping.ma2@windriver.com>
Link: https://lore.kernel.org/r/1589165527-188401-1-git-send-email-jiping.ma2@windriver.com


[will: Shuffled code and added a comment]
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent cb944f02
......@@ -15,15 +15,34 @@ u64 perf_reg_value(struct pt_regs *regs, int idx)
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)
......
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