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diff --git a/Documentation/powerpc/ptrace.rst b/Documentation/powerpc/ptrace.rst new file mode 100644 index 000000000..77725d69e --- /dev/null +++ b/Documentation/powerpc/ptrace.rst @@ -0,0 +1,157 @@ +====== +Ptrace +====== + +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 + #define PPC_DEBUG_FEATURE_DATA_BP_DAWR 0x10 + #define PPC_DEBUG_FEATURE_DATA_BP_ARCH_31 0x20 + +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; + +- set a watchpoint in server processors (BookS):: + + p.version = 1; + p.trigger_type = PPC_BREAKPOINT_TRIGGER_RW; + p.addr_mode = PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE; + or + p.addr_mode = PPC_BREAKPOINT_MODE_EXACT; + + p.condition_mode = PPC_BREAKPOINT_CONDITION_NONE; + p.addr = (uint64_t) begin_range; + /* For PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE addr2 needs to be specified, where + * addr2 - addr <= 8 Bytes. + */ + 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.. |