[RFC:PATCH 00/03] powerpc: Expose BookE debug registers through extended ptrace interface

[Kumar Gala]

On Dec 10, 2009, at 9:57 AM, Dave Kleikamp wrote:

> These patches implement an extention to the ptrace interface proposed by
> Thiago Bauermann and the the PowerPC gdb team.
> 
> 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 propose the
> following 3 new ptrace requests described below.
> 
> There have been discussions of a generic hardware debug interface for the
> kernel which would hopefully contemplate all the functionality below and
> supersede it.  But we need something that works now, and which enables GDB
> to be simpler and work with both Server and Embedded processors without
> special cases.
> 
> 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

Is GDB smart enough to deal w/no condition_regs?  On some Book-E devices we have 2 IACs, 2 DACs, and 0 DVCs.  Does it need to be in the features?

- k