Messages in this thread | | | Date | Tue, 9 Aug 2016 18:27:55 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v2 30/44] x86/unwind: add new unwind interface and implementations |
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On Tue, Aug 09, 2016 at 06:17:41PM -0500, Nilay Vaish wrote: > On 4 August 2016 at 17:22, Josh Poimboeuf <jpoimboe@redhat.com> wrote: > > diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c > > new file mode 100644 > > index 0000000..f28f1b5 > > --- /dev/null > > +++ b/arch/x86/kernel/unwind_frame.c > > @@ -0,0 +1,84 @@ > > +#include <linux/sched.h> > > +#include <asm/ptrace.h> > > +#include <asm/bitops.h> > > +#include <asm/stacktrace.h> > > +#include <asm/unwind.h> > > + > > +#define FRAME_HEADER_SIZE (sizeof(long) * 2) > > + > > +unsigned long unwind_get_return_address(struct unwind_state *state) > > +{ > > + unsigned long *addr_p = unwind_get_return_address_ptr(state); > > + unsigned long addr; > > + > > + if (state->stack_info.type == STACK_TYPE_UNKNOWN) > > + return 0; > > + > > + addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, *addr_p, > > + addr_p); > > + > > + return __kernel_text_address(addr) ? addr : 0; > > +} > > +EXPORT_SYMBOL_GPL(unwind_get_return_address); > > + > > +static bool update_stack_state(struct unwind_state *state, void *addr, > > + size_t len) > > +{ > > + struct stack_info *info = &state->stack_info; > > + > > + if (on_stack(info, addr, len)) > > + return true; > > + > > + if (get_stack_info(info->next_sp, state->task, info, > > + &state->stack_mask)) > > + goto unknown; > > + > > + if (!on_stack(info, addr, len)) > > + goto unknown; > > + > > + return true; > > + > > +unknown: > > + info->type = STACK_TYPE_UNKNOWN; > > + return false; > > +} > > + > > +bool unwind_next_frame(struct unwind_state *state) > > +{ > > + unsigned long *next_bp; > > + > > + if (unwind_done(state)) > > + return false; > > + > > + next_bp = (unsigned long *)*state->bp; > > + > > + /* > > + * Make sure the next frame is on a valid stack and can be accessed > > + * safely. > > + */ > > + if (!update_stack_state(state, next_bp, FRAME_HEADER_SIZE)) > > + return false; > > + > > + /* move to the next frame */ > > + state->bp = next_bp; > > + return true; > > +} > > +EXPORT_SYMBOL_GPL(unwind_next_frame); > > + > > +void __unwind_start(struct unwind_state *state, struct task_struct *task, > > + struct pt_regs *regs, unsigned long *sp) > > +{ > > + memset(state, 0, sizeof(*state)); > > + > > + state->task = task; > > + state->bp = get_frame_pointer(task, regs); > > + > > + get_stack_info(state->bp, state->task, &state->stack_info, > > + &state->stack_mask); > > + update_stack_state(state, state->bp, FRAME_HEADER_SIZE); > > + > > + /* unwind to the first frame after the specified stack pointer */ > > + while (state->bp < sp && !unwind_done(state)) > > + unwind_next_frame(state); > > Do we unwind all the frames here? It seems strange to me that in a > function named __unwind_start(), we unwind all the frames.
It just skips any stack frames before the specified "sp" pointer. Several callers use this, for example, to start at regs->sp instead of the current stack frame. I'll try to make the comment clearer.
> > +} > > +EXPORT_SYMBOL_GPL(__unwind_start); > > diff --git a/arch/x86/kernel/unwind_guess.c b/arch/x86/kernel/unwind_guess.c > > new file mode 100644 > > index 0000000..e03df5a > > --- /dev/null > > +++ b/arch/x86/kernel/unwind_guess.c > > @@ -0,0 +1,40 @@ > > +#include <linux/sched.h> > > +#include <linux/ftrace.h> > > +#include <asm/ptrace.h> > > +#include <asm/bitops.h> > > +#include <asm/stacktrace.h> > > +#include <asm/unwind.h> > > + > > +bool unwind_next_frame(struct unwind_state *state) > > +{ > > + struct stack_info *info = &state->stack_info; > > + > > + if (info->type == STACK_TYPE_UNKNOWN) > > + return false; > > + > > + do { > > + for (state->sp++; state->sp < info->end; state->sp++) > > + if (__kernel_text_address(*state->sp)) > > + return true; > > + > > + state->sp = info->next_sp; > > + > > + } while (!get_stack_info(state->sp, state->task, info, > > + &state->stack_mask)); > > + > > + return false; > > +} > > + > > +void __unwind_start(struct unwind_state *state, struct task_struct *task, > > + struct pt_regs *regs, unsigned long *sp) > > +{ > > + memset(state, 0, sizeof(*state)); > > + > > + state->task = task; > > + state->sp = sp; > > + > > + get_stack_info(sp, state->task, &state->stack_info, &state->stack_mask); > > + > > + if (!__kernel_text_address(*sp)) > > + unwind_next_frame(state); > > +} > > -- > > 2.7.4 > > > > Why is it that you need to export symbols in unwind_frame.c but not in > unwind_guess.c. As per the Makefile, we would be compiling either of > those two files. Should not EXPORT_SYMBOL_GPL(__unwind_start) appear > in both files?
Yeah, good catch.
-- Josh
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