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authorDave Kleikamp <shaggy@linux.vnet.ibm.com>2010-02-08 11:51:05 (GMT)
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2010-02-17 03:03:17 (GMT)
commit3162d92dfb79a0b5fc03380b8819fa5f870ebf1e (patch)
tree490c54c78630be6052200432d249596bf2f3ae62 /Documentation/powerpc
parent172ae2e7f8ff9053905a36672453a6d2ff95b182 (diff)
powerpc: Extended ptrace interface
powerpc: Extended ptrace interface From: Dave Kleikamp <shaggy@linux.vnet.ibm.com> Based on patches originally written by Torez Smith. Add a new extended ptrace interface so that user-space has a single interface for powerpc, without having to know the specific layout of the debug registers. Implement: PPC_PTRACE_GETHWDEBUGINFO PPC_PTRACE_SETHWDEBUG PPC_PTRACE_DELHWDEBUG Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com> Acked-by: David Gibson <dwg@au1.ibm.com> Cc: Torez Smith <lnxtorez@linux.vnet.ibm.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Josh Boyer <jwboyer@linux.vnet.ibm.com> Cc: Kumar Gala <galak@kernel.crashing.org> Cc: Sergio Durigan Junior <sergiodj@br.ibm.com> Cc: Thiago Jung Bauermann <bauerman@br.ibm.com> Cc: linuxppc-dev list <Linuxppc-dev@ozlabs.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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+GDB intends to support the following hardware debug features of BookE
+processors:
+
+4 hardware breakpoints (IAC)
+2 hardware watchpoints (read, write and read-write) (DAC)
+2 value conditions for the hardware watchpoints (DVC)
+
+For that, we need to extend ptrace so that GDB can query and set these
+resources. Since we're extending, we're trying to create an interface
+that's extendable and that covers both BookE and server processors, so
+that GDB doesn't need to special-case each of them. We added the
+following 3 new ptrace requests.
+
+1. PTRACE_PPC_GETHWDEBUGINFO
+
+Query for GDB to discover the hardware debug features. The main info to
+be returned here is the minimum alignment for the hardware watchpoints.
+BookE processors don't have restrictions here, but server processors have
+an 8-byte alignment restriction for hardware watchpoints. We'd like to avoid
+adding special cases to GDB based on what it sees in AUXV.
+
+Since we're at it, we added other useful info that the kernel can return to
+GDB: this query will return the number of hardware breakpoints, hardware
+watchpoints and whether it supports a range of addresses and a condition.
+The query will fill the following structure provided by the requesting process:
+
+struct ppc_debug_info {
+ unit32_t version;
+ unit32_t num_instruction_bps;
+ unit32_t num_data_bps;
+ unit32_t num_condition_regs;
+ unit32_t data_bp_alignment;
+ unit32_t sizeof_condition; /* size of the DVC register */
+ uint64_t features; /* bitmask of the individual flags */
+};
+
+features will have bits indicating whether there is support for:
+
+#define PPC_DEBUG_FEATURE_INSN_BP_RANGE 0x1
+#define PPC_DEBUG_FEATURE_INSN_BP_MASK 0x2
+#define PPC_DEBUG_FEATURE_DATA_BP_RANGE 0x4
+#define PPC_DEBUG_FEATURE_DATA_BP_MASK 0x8
+
+2. PTRACE_SETHWDEBUG
+
+Sets a hardware breakpoint or watchpoint, according to the provided structure:
+
+struct ppc_hw_breakpoint {
+ uint32_t version;
+#define PPC_BREAKPOINT_TRIGGER_EXECUTE 0x1
+#define PPC_BREAKPOINT_TRIGGER_READ 0x2
+#define PPC_BREAKPOINT_TRIGGER_WRITE 0x4
+ uint32_t trigger_type; /* only some combinations allowed */
+#define PPC_BREAKPOINT_MODE_EXACT 0x0
+#define PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE 0x1
+#define PPC_BREAKPOINT_MODE_RANGE_EXCLUSIVE 0x2
+#define PPC_BREAKPOINT_MODE_MASK 0x3
+ uint32_t addr_mode; /* address match mode */
+
+#define PPC_BREAKPOINT_CONDITION_MODE 0x3
+#define PPC_BREAKPOINT_CONDITION_NONE 0x0
+#define PPC_BREAKPOINT_CONDITION_AND 0x1
+#define PPC_BREAKPOINT_CONDITION_EXACT 0x1 /* different name for the same thing as above */
+#define PPC_BREAKPOINT_CONDITION_OR 0x2
+#define PPC_BREAKPOINT_CONDITION_AND_OR 0x3
+#define PPC_BREAKPOINT_CONDITION_BE_ALL 0x00ff0000 /* byte enable bits */
+#define PPC_BREAKPOINT_CONDITION_BE(n) (1<<((n)+16))
+ uint32_t condition_mode; /* break/watchpoint condition flags */
+
+ uint64_t addr;
+ uint64_t addr2;
+ uint64_t condition_value;
+};
+
+A request specifies one event, not necessarily just one register to be set.
+For instance, if the request is for a watchpoint with a condition, both the
+DAC and DVC registers will be set in the same request.
+
+With this GDB can ask for all kinds of hardware breakpoints and watchpoints
+that the BookE supports. COMEFROM breakpoints available in server processors
+are not contemplated, but that is out of the scope of this work.
+
+ptrace will return an integer (handle) uniquely identifying the breakpoint or
+watchpoint just created. This integer will be used in the PTRACE_DELHWDEBUG
+request to ask for its removal. Return -ENOSPC if the requested breakpoint
+can't be allocated on the registers.
+
+Some examples of using the structure to:
+
+- set a breakpoint in the first breakpoint register
+
+ p.version = PPC_DEBUG_CURRENT_VERSION;
+ p.trigger_type = PPC_BREAKPOINT_TRIGGER_EXECUTE;
+ p.addr_mode = PPC_BREAKPOINT_MODE_EXACT;
+ p.condition_mode = PPC_BREAKPOINT_CONDITION_NONE;
+ p.addr = (uint64_t) address;
+ p.addr2 = 0;
+ p.condition_value = 0;
+
+- set a watchpoint which triggers on reads in the second watchpoint register
+
+ p.version = PPC_DEBUG_CURRENT_VERSION;
+ p.trigger_type = PPC_BREAKPOINT_TRIGGER_READ;
+ p.addr_mode = PPC_BREAKPOINT_MODE_EXACT;
+ p.condition_mode = PPC_BREAKPOINT_CONDITION_NONE;
+ p.addr = (uint64_t) address;
+ p.addr2 = 0;
+ p.condition_value = 0;
+
+- set a watchpoint which triggers only with a specific value
+
+ p.version = PPC_DEBUG_CURRENT_VERSION;
+ p.trigger_type = PPC_BREAKPOINT_TRIGGER_READ;
+ p.addr_mode = PPC_BREAKPOINT_MODE_EXACT;
+ p.condition_mode = PPC_BREAKPOINT_CONDITION_AND | PPC_BREAKPOINT_CONDITION_BE_ALL;
+ p.addr = (uint64_t) address;
+ p.addr2 = 0;
+ p.condition_value = (uint64_t) condition;
+
+- set a ranged hardware breakpoint
+
+ p.version = PPC_DEBUG_CURRENT_VERSION;
+ p.trigger_type = PPC_BREAKPOINT_TRIGGER_EXECUTE;
+ p.addr_mode = PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE;
+ p.condition_mode = PPC_BREAKPOINT_CONDITION_NONE;
+ p.addr = (uint64_t) begin_range;
+ p.addr2 = (uint64_t) end_range;
+ p.condition_value = 0;
+
+3. PTRACE_DELHWDEBUG
+
+Takes an integer which identifies an existing breakpoint or watchpoint
+(i.e., the value returned from PTRACE_SETHWDEBUG), and deletes the
+corresponding breakpoint or watchpoint..

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