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Date: Wed, 04 Dec 2013 19:23:02 +0200
From: Taras Kondratiuk <taras.kondratiuk@...aro.org>
To: David Long <dave.long@...aro.org>
CC: linux-arm-kernel@...ts.infradead.org,
Russell King <linux@....linux.org.uk>,
Rabin Vincent <rabin@....in>,
"Jon Medhurst (Tixy)" <tixy@...aro.org>,
Oleg Nesterov <oleg@...hat.com>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...hat.com>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
davem@...emloft.net, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Paul Mackerras <paulus@...ba.org>,
Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 14/15] ARM: add uprobes support
On 11/27/2013 04:53 AM, David Long wrote:
> From: "David A. Long" <dave.long@...aro.org>
>
> Using Rabin Vincent's ARM uprobes patches as a base, enable uprobes
> support on ARM.
>
> Caveats:
>
> - Thumb is not supported
> - XOL abort/trap handling is not implemented
>
> Signed-off-by: David A. Long <dave.long@...aro.org>
> ---
> arch/arm/Kconfig | 4 +
> arch/arm/include/asm/ptrace.h | 6 +
> arch/arm/include/asm/thread_info.h | 5 +-
> arch/arm/include/asm/uprobes.h | 34 ++++++
> arch/arm/kernel/Makefile | 1 +
> arch/arm/kernel/signal.c | 4 +
> arch/arm/kernel/uprobes-arm.c | 223 +++++++++++++++++++++++++++++++++++++
> arch/arm/kernel/uprobes.c | 198 ++++++++++++++++++++++++++++++++
> arch/arm/kernel/uprobes.h | 27 +++++
> 9 files changed, 501 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm/include/asm/uprobes.h
> create mode 100644 arch/arm/kernel/uprobes-arm.c
> create mode 100644 arch/arm/kernel/uprobes.c
> create mode 100644 arch/arm/kernel/uprobes.h
>
[snip]
> diff --git a/arch/arm/kernel/uprobes-arm.c b/arch/arm/kernel/uprobes-arm.c
> new file mode 100644
> index 0000000..0a83ad7
> --- /dev/null
> +++ b/arch/arm/kernel/uprobes-arm.c
> @@ -0,0 +1,223 @@
> +#include <linux/kernel.h>
> +#include <linux/wait.h>
> +#include <linux/uprobes.h>
> +#include <linux/module.h>
> +
> +#include "probes.h"
> +#include "probes-arm.h"
> +#include "uprobes.h"
> +
> +static int uprobes_substitute_pc(unsigned long *pinsn, u32 oregs)
> +{
> + probes_opcode_t insn = *pinsn;
In a current implementation pinsn points to an ixol field of arch_uprobe
structure, which has native endianness and is written via
__opcode_to_mem_arm() macro in arch_uprobe_analyze_insn() function.
So *pinsn should be wrapped with __opcode_to_mem_arm/__mem_to_opcode_arm()
macros in this function.
> + probes_opcode_t temp;
> + probes_opcode_t mask;
> + int freereg;
> + u32 free = 0xffff;
> + u32 regs;
> +
> + for (regs = oregs; regs; regs >>= 4, insn >>= 4) {
> + if ((regs & 0xf) == REG_TYPE_NONE)
> + continue;
> +
> + free &= ~(1 << (insn & 0xf));
> + }
> +
> + /* No PC, no problem */
> + if (free & (1 << 15))
> + return 15;
> +
> + if (!free)
> + return -1;
> +
> + /*
> + * fls instead of ffs ensures that for "ldrd r0, r1, [pc]" we would
> + * pick LR instead of R1.
> + */
> + freereg = free = fls(free) - 1;
> +
> + temp = *pinsn;
> + insn = *pinsn;
> + regs = oregs;
> + mask = 0xf;
> +
> + for (; regs; regs >>= 4, mask <<= 4, free <<= 4, temp >>= 4) {
> + if ((regs & 0xf) == REG_TYPE_NONE)
> + continue;
> +
> + if ((temp & 0xf) != 15)
> + continue;
> +
> + insn &= ~mask;
> + insn |= free & mask;
> + }
> +
> + *pinsn = insn;
> + return freereg;
> +}
> +
[snip]
> +
> +enum probes_insn
> +uprobe_decode_ldmstm(probes_opcode_t insn,
> + struct arch_specific_insn *asi, struct decode_header *d)
> +{
> + struct arch_uprobe *auprobe = container_of(asi, struct arch_uprobe,
> + asi);
> + unsigned reglist = insn & 0xffff;
> + int rn = (insn >> 16) & 0xf;
> + int lbit = insn & (1 << 20);
> + unsigned used = reglist | (1 << rn);
> +
> + if (rn == 15)
> + return INSN_REJECTED;
> +
> + if (!(used & (1 << 15)))
> + return INSN_GOOD;
> +
> + if (used & (1 << 14))
> + return INSN_REJECTED;
> +
> + /* Use LR instead of PC */
> + insn ^= 0xc000;
> +
> + auprobe->pcreg = 14;
> + auprobe->ixol[0] = insn;
insn contains canonical opcode, but ixol should contain
an opcode in native endianness. So it should be
auprobe->ixol[0] = __opcode_to_mem_arm(insn);
> +
> + auprobe->prehandler = uprobe_set_pc;
> + if (lbit)
> + auprobe->posthandler = uprobe_write_pc;
> + else
> + auprobe->posthandler = uprobe_unset_pc;
> +
> + return INSN_GOOD;
> +}
> +
--
Taras Kondratiuk
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