| Message ID | 1411977842-16515-2-git-send-email-victor.kamensky@linaro.org |
|---|---|
| State | New |
| Headers | show |
Hi Victor, On Mon, Sep 29, 2014 at 09:04:02AM +0100, Victor Kamensky wrote: > hw_break_set function that performs ptrace_regset for hardware > breakpoints and watchpoints needs to take into account actual > number of hardware breakpoints and watchpoints available in CPU. > > Current code iterates over all 16 entries of 'struct user_hwdebug_state' > and tries to reserve hardware breakpoint for each index, which fails > if CPU supports less than 16 hardware breakpoints. One manifestation of > the issue is that gdb fails to debug multithreaded user land application > and exits with 'Unexpected error setting hardware debug registers' > error - ptrace system call for hardware breakpoints regset fails with > ENOSPC. When does this happen? hw_break_set is driven by userspace, so if GDB is asking for more registers than we actually have, then this is a GDB bug and the kernel is doing the right thing. Have you reproduced this with the latest version of GDB? Will
Hi Will, On 29 September 2014 03:16, Will Deacon <will.deacon@arm.com> wrote: > Hi Victor, > > On Mon, Sep 29, 2014 at 09:04:02AM +0100, Victor Kamensky wrote: >> hw_break_set function that performs ptrace_regset for hardware >> breakpoints and watchpoints needs to take into account actual >> number of hardware breakpoints and watchpoints available in CPU. >> >> Current code iterates over all 16 entries of 'struct user_hwdebug_state' >> and tries to reserve hardware breakpoint for each index, which fails >> if CPU supports less than 16 hardware breakpoints. One manifestation of >> the issue is that gdb fails to debug multithreaded user land application >> and exits with 'Unexpected error setting hardware debug registers' >> error - ptrace system call for hardware breakpoints regset fails with >> ENOSPC. > > When does this happen? hw_break_set is driven by userspace, so if GDB is > asking for more registers than we actually have, then this is a GDB bug and > the kernel is doing the right thing. > > Have you reproduced this with the latest version of GDB? Thank you for the reply. Just checked latest version of GDB, indeed it does not have my original issue. It turns out my gdb is based on some old linaro gdb version that unconditionally passes sizeof(user_hwdebug_state) as iov.len to PTRACE_SETREGSET with note type NT_ARM_HW_BREAK. Latest gdb adjusts iov.len based on available number of hardware breakpoints. I should have checked latest gdb before posting this. Naturally previously suggested patch is withdrawn. Question is there any place where variable payload nature of PTRACE_SETREGSET with note type NT_ARM_HW_BREAK and NT_ARM_HW_WATCH documented? I've tried kernel Documentation directory, aarch64 abi document, http://infocenter.arm.com search, none of them mention NT_ARM_HW_BREAK. Just curious is there any place for that sort of information to look in the future. If answer that it is documented by existing kernel/gdb code :), please feel free to ignore this question. Thanks, Victor > Will
Hi Victor, On 09/29/2014 01:49 PM, Victor Kamensky wrote: > Hi Will, > > On 29 September 2014 03:16, Will Deacon <will.deacon@arm.com> wrote: >> Hi Victor, >> >> On Mon, Sep 29, 2014 at 09:04:02AM +0100, Victor Kamensky wrote: >>> hw_break_set function that performs ptrace_regset for hardware >>> breakpoints and watchpoints needs to take into account actual >>> number of hardware breakpoints and watchpoints available in CPU. >>> >>> Current code iterates over all 16 entries of 'struct user_hwdebug_state' >>> and tries to reserve hardware breakpoint for each index, which fails >>> if CPU supports less than 16 hardware breakpoints. One manifestation of >>> the issue is that gdb fails to debug multithreaded user land application >>> and exits with 'Unexpected error setting hardware debug registers' >>> error - ptrace system call for hardware breakpoints regset fails with >>> ENOSPC. >> >> When does this happen? hw_break_set is driven by userspace, so if GDB is >> asking for more registers than we actually have, then this is a GDB bug and >> the kernel is doing the right thing. >> >> Have you reproduced this with the latest version of GDB? > > Thank you for the reply. Just checked latest version of GDB, indeed it > does not have my original issue. It turns out my gdb is based on some > old linaro gdb version that unconditionally passes sizeof(user_hwdebug_state) > as iov.len to PTRACE_SETREGSET with note type NT_ARM_HW_BREAK. > Latest gdb adjusts iov.len based on available number of hardware breakpoints. > I should have checked latest gdb before posting this. Naturally previously > suggested patch is withdrawn. > > Question is there any place where variable payload nature of > PTRACE_SETREGSET with note type NT_ARM_HW_BREAK and > NT_ARM_HW_WATCH documented? I've tried kernel Documentation > directory, aarch64 abi document, http://infocenter.arm.com search, none > of them mention NT_ARM_HW_BREAK. Just curious is there any place > for that sort of information to look in the future. If answer that it is > documented by existing kernel/gdb code :), please feel free to ignore > this question. While it doesn't address those specific note types (yet): http://man7.org/linux/man-pages/man2/ptrace.2.html PTRACE_GETREGSET (since Linux 2.6.34) Read the tracee's registers. addr specifies, in an architecture-dependent way, the type of registers to be read. NT_PRSTATUS (with numerical value 1) usually results in reading of general-purpose registers. If the CPU has, for example, floating-point and/or vector registers, they can be retrieved by setting addr to the corresponding NT_foo constant. data points to a struct iovec, which describes the destination buffer's location and length. On return, the kernel modifies iov.len to indicate the actual number of bytes returned. PTRACE_SETREGSET (since Linux 2.6.34) Modify the tracee's registers. The meaning of addr and data is analogous to PTRACE_GETREGSET. Perhaps this could be expanded upon. https://www.kernel.org/doc/man-pages/patches.html Christopher
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index fe63ac5..4178ba1 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -248,22 +248,32 @@ static int ptrace_hbp_fill_attr_ctrl(unsigned int note_type, return 0; } -static int ptrace_hbp_get_resource_info(unsigned int note_type, u32 *info) +static int ptrace_hbp_get_num_slots(unsigned int note_type, u8 *num) { - u8 num; - u32 reg = 0; - switch (note_type) { case NT_ARM_HW_BREAK: - num = hw_breakpoint_slots(TYPE_INST); + *num = hw_breakpoint_slots(TYPE_INST); break; case NT_ARM_HW_WATCH: - num = hw_breakpoint_slots(TYPE_DATA); + *num = hw_breakpoint_slots(TYPE_DATA); break; default: return -EINVAL; } + return 0; +} + +static int ptrace_hbp_get_resource_info(unsigned int note_type, u32 *info) +{ + u8 num; + u32 reg = 0; + int err; + + err = ptrace_hbp_get_num_slots(note_type, &num); + if (err) + return err; + reg |= debug_monitors_arch(); reg <<= 8; reg |= num; @@ -432,6 +442,11 @@ static int hw_break_set(struct task_struct *target, int ret, idx = 0, offset, limit; u32 ctrl; u64 addr; + u8 num_slots; + + ret = ptrace_hbp_get_num_slots(note_type, &num_slots); + if (ret) + return ret; /* Resource info and pad */ offset = offsetof(struct user_hwdebug_state, dbg_regs); @@ -441,7 +456,7 @@ static int hw_break_set(struct task_struct *target, /* (address, ctrl) registers */ limit = regset->n * regset->size; - while (count && offset < limit) { + while ((count && offset < limit) && (idx < num_slots)) { ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &addr, offset, offset + PTRACE_HBP_ADDR_SZ); if (ret)
hw_break_set function that performs ptrace_regset for hardware breakpoints and watchpoints needs to take into account actual number of hardware breakpoints and watchpoints available in CPU. Current code iterates over all 16 entries of 'struct user_hwdebug_state' and tries to reserve hardware breakpoint for each index, which fails if CPU supports less than 16 hardware breakpoints. One manifestation of the issue is that gdb fails to debug multithreaded user land application and exits with 'Unexpected error setting hardware debug registers' error - ptrace system call for hardware breakpoints regset fails with ENOSPC. Solution is to read number of available hardware breakpoints and watchpoints available in CPU and process only that number of first entries in passed 'struct user_hwdebug_state' regset. Code assumes that ptrace caller uses only first entries in 'struct user_hwdebug_state' up to number of hardware breakpoints and watchpoints supported by CPU. I.e there are no "ignore me, empty" entries in the middle of 'struct user_hwdebug_state' entries array. Signed-off-by: Victor Kamensky <victor.kamensky@linaro.org> --- arch/arm64/kernel/ptrace.c | 29 ++++++++++++++++++++++------- 1 file changed, 22 insertions(+), 7 deletions(-)