Re: [PATCH kvm-unit-tests v5 1/5] lib: backtrace printing

[Andrew Jones <drjones@redhat.com>]

On Mon, Mar 07, 2016 at 09:46:53AM -0800, Peter Feiner wrote:
> Functions to walk stack and print backtrace. The stack's unadorned as
> 
> 	STACK: [@]addr addr addr ...
> 
> where the optional @ indicates that addr isn't a return address.
> 
> A follow-up patch post-processes the output to pretty-print the stack.
> 
> Frame stack walker is just a stub on arm and ppc.
> 
> Signed-off-by: Peter Feiner <pfeiner@google.com>
> ---
>  Makefile                |  6 ++--
>  lib/arm/asm/stack.h     |  0
>  lib/arm64/asm/stack.h   |  0
>  lib/asm-generic/stack.c |  3 ++
>  lib/libcflat.h          |  3 ++
>  lib/powerpc/asm/stack.h |  0
>  lib/ppc64/asm/stack.h   |  0
>  lib/stack.c             | 96 +++++++++++++++++++++++++++++++++++++++++++++++++
>  lib/stack.h             | 20 +++++++++++
>  lib/x86/asm/stack.h     | 18 ++++++++++
>  lib/x86/stack.c         | 25 +++++++++++++
>  x86/Makefile.common     |  4 +++
>  12 files changed, 173 insertions(+), 2 deletions(-)
>  create mode 100644 lib/arm/asm/stack.h
>  create mode 100644 lib/arm64/asm/stack.h
>  create mode 100644 lib/asm-generic/stack.c
>  create mode 100644 lib/powerpc/asm/stack.h
>  create mode 100644 lib/ppc64/asm/stack.h
>  create mode 100644 lib/stack.c
>  create mode 100644 lib/stack.h
>  create mode 100644 lib/x86/asm/stack.h
>  create mode 100644 lib/x86/stack.c
> 
> diff --git a/Makefile b/Makefile
> index 72e6711..c53aff6 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -22,7 +22,8 @@ cflatobjs := \
>  	lib/printf.o \
>  	lib/string.o \
>  	lib/abort.o \
> -	lib/report.o
> +	lib/report.o \
> +	lib/stack.o
>  
>  # libfdt paths
>  LIBFDT_objdir = lib/libfdt
> @@ -42,7 +43,8 @@ cc-option = $(shell if $(CC) $(1) -S -o /dev/null -xc /dev/null \
>  
>  CFLAGS += -g
>  CFLAGS += $(autodepend-flags) -Wall
> -CFLAGS += $(call cc-option, -fomit-frame-pointer, "")
> +frame-pointer-flag=-f$(if $(KEEP_FRAME_POINTER),no-,)omit-frame-pointer
> +CFLAGS += $(call cc-option, $(frame-pointer-flag), "")
>  CFLAGS += $(call cc-option, -fno-stack-protector, "")
>  CFLAGS += $(call cc-option, -fno-stack-protector-all, "")
>  
> diff --git a/lib/arm/asm/stack.h b/lib/arm/asm/stack.h
> new file mode 100644
> index 0000000..e69de29
> diff --git a/lib/arm64/asm/stack.h b/lib/arm64/asm/stack.h
> new file mode 100644
> index 0000000..e69de29
> diff --git a/lib/asm-generic/stack.c b/lib/asm-generic/stack.c
> new file mode 100644
> index 0000000..40c67c2
> --- /dev/null
> +++ b/lib/asm-generic/stack.c
> @@ -0,0 +1,3 @@
> +#include <libcflat.h>
> +#include <asm-generic/stack.h>
> +

Looks like you forgot to remove this file.

> diff --git a/lib/libcflat.h b/lib/libcflat.h
> index b58a8a1..55bddca 100644
> --- a/lib/libcflat.h
> +++ b/lib/libcflat.h
> @@ -81,6 +81,9 @@ extern void report_xfail(const char *msg_fmt, bool xfail, bool pass, ...);
>  extern void report_abort(const char *msg_fmt, ...);
>  extern int report_summary(void);
>  
> +extern void dump_stack(void);
> +extern void dump_frame_stack(const void *instruction, const void *frame);
> +
>  #define ARRAY_SIZE(_a) (sizeof(_a)/sizeof((_a)[0]))
>  
>  #define container_of(ptr, type, member) ({				\
> diff --git a/lib/powerpc/asm/stack.h b/lib/powerpc/asm/stack.h
> new file mode 100644
> index 0000000..e69de29
> diff --git a/lib/ppc64/asm/stack.h b/lib/ppc64/asm/stack.h
> new file mode 100644
> index 0000000..e69de29
> diff --git a/lib/stack.c b/lib/stack.c
> new file mode 100644
> index 0000000..035fe27
> --- /dev/null
> +++ b/lib/stack.c
> @@ -0,0 +1,96 @@
> +#include <libcflat.h>
> +#include <stack.h>
> +
> +#define MAX_DEPTH 20
> +
> +static void print_stack(const void **return_addrs, int depth,
> +			bool top_is_return_address)
> +{
> +	int i = 0;
> +
> +	printf("\tSTACK:");
> +
> +	/* @addr indicates a non-return address, as expected by the stack
> +	 * pretty printer script. */
> +	if (depth > 0 && !top_is_return_address) {
> +		printf(" @%lx", (unsigned long) return_addrs[0]);
> +		i++;
> +	}
> +
> +	for (; i < depth; i++) {
> +		printf(" %lx", (unsigned long) return_addrs[i]);
> +	}
> +	printf("\n");
> +}
> +
> +void dump_stack(void)
> +{
> +	const void *return_addrs[MAX_DEPTH];
> +	int depth;
> +
> +	depth = backtrace(return_addrs, MAX_DEPTH);
> +	print_stack(return_addrs, depth, true);
> +}
> +
> +void dump_frame_stack(const void *instruction, const void *frame)
> +{
> +	const void *return_addrs[MAX_DEPTH];
> +	int depth;
> +
> +	return_addrs[0] = instruction;
> +	depth = backtrace_frame(frame, &return_addrs[1], MAX_DEPTH - 1);
> +	print_stack(return_addrs, depth + 1, false);
> +}
> +
> +#ifndef HAVE_ARCH_BACKTRACE
> +int backtrace(const void **return_addrs, int max_depth)
> +{
> +	static int walking;
> +	int depth = 0;
> +	void *addr;
> +
> +	if (walking) {
> +		printf("RECURSIVE STACK WALK!!!\n");
> +		return 0;
> +	}
> +	walking = 1;
> +
> +	/* __builtin_return_address requires a compile-time constant argument */
> +#define GET_RETURN_ADDRESS(i)						\
> +	if (max_depth == i)						\
> +		goto done;						\
> +	addr = __builtin_return_address(i + 1);				\

Is the +1 to skip a level, which means addr is an address two levels up?
If we do that, then won't we skip the callers of backtrace, which may or
may not be dump_stack?


> +	if (!addr)							\
> +		goto done;						\
> +	return_addrs[i] = __builtin_extract_return_addr(addr);		\

So here we put the i+1th return address into return_addrs[i]. I find
that a bit confusing. Maybe we should leave it to the callers of
backtrace to do any level skipping they want, i.e. here we shouldn't
skip anything, but dump_stack could start printing at i=1.


> +	depth = i + 1;							\
> +
> +	GET_RETURN_ADDRESS(0)
> +	GET_RETURN_ADDRESS(1)
> +	GET_RETURN_ADDRESS(2)
> +	GET_RETURN_ADDRESS(3)
> +	GET_RETURN_ADDRESS(4)
> +	GET_RETURN_ADDRESS(5)
> +	GET_RETURN_ADDRESS(6)
> +	GET_RETURN_ADDRESS(7)
> +	GET_RETURN_ADDRESS(8)
> +	GET_RETURN_ADDRESS(9)
> +	GET_RETURN_ADDRESS(10)
> +	GET_RETURN_ADDRESS(11)
> +	GET_RETURN_ADDRESS(12)
> +	GET_RETURN_ADDRESS(13)
> +	GET_RETURN_ADDRESS(14)
> +	GET_RETURN_ADDRESS(15)
> +	GET_RETURN_ADDRESS(16)
> +	GET_RETURN_ADDRESS(17)
> +	GET_RETURN_ADDRESS(18)
> +	GET_RETURN_ADDRESS(19)
> +	GET_RETURN_ADDRESS(20)
> +
> +#undef GET_RETURN_ADDRESS
> +
> +done:
> +	walking = 0;
> +	return depth;
> +}
> +#endif  /* HAVE_ARCH_BACKTRACE */
> diff --git a/lib/stack.h b/lib/stack.h
> new file mode 100644
> index 0000000..bb6b9aa
> --- /dev/null
> +++ b/lib/stack.h
> @@ -0,0 +1,20 @@
> +#ifndef _STACK_H_
> +#define _STACK_H_
> +
> +#include <libcflat.h>
> +#include <asm/stack.h>
> +
> +#ifndef HAVE_ARCH_BACKTRACE_FRAME
> +static inline int
> +backtrace_frame(const void *frame __unused, const void **return_addrs __unused,
> +		int max_depth __unused)
> +{
> +	return 0;
> +}
> +#endif
> +
> +#ifndef HAVE_ARCH_BACKTRACE
> +int backtrace(const void **return_addrs, int max_depth);
> +#endif
> +
> +#endif
> diff --git a/lib/x86/asm/stack.h b/lib/x86/asm/stack.h
> new file mode 100644
> index 0000000..bb1c2c0
> --- /dev/null
> +++ b/lib/x86/asm/stack.h
> @@ -0,0 +1,18 @@
> +#ifndef _X86ASM_STACK_H_
> +#define _X86ASM_STACK_H_
> +
> +#ifndef _STACK_H_
> +#error Do not directly include <asm/stack.h>. Just use <stack.h>.
> +#endif
> +
> +#define HAVE_ARCH_BACKTRACE_FRAME
> +int backtrace_frame(const void *frame, const void **return_addrs, int max_depth);
> +
> +#define HAVE_ARCH_BACKTRACE
> +static inline int backtrace(const void **return_addrs, int max_depth)
> +{
> +	return backtrace_frame(__builtin_frame_address(0), return_addrs,
> +			       max_depth);
> +}
> +
> +#endif
> diff --git a/lib/x86/stack.c b/lib/x86/stack.c
> new file mode 100644
> index 0000000..3227800
> --- /dev/null
> +++ b/lib/x86/stack.c
> @@ -0,0 +1,25 @@
> +#include <libcflat.h>
> +#include <stack.h>
> +
> +int backtrace_frame(const void *frame, const void **return_addrs, int max_depth)
> +{
> +	static int walking;
> +	int depth = 0;
> +	const unsigned long *bp = (unsigned long *) frame;
> +
> +	if (walking) {
> +		printf("RECURSIVE STACK WALK!!!\n");
> +		return 0;
> +	}
> +	walking = 1;
> +
> +	for (depth = 0; depth < max_depth; depth++) {
> +		return_addrs[depth] = (void *) bp[1];
> +		if (return_addrs[depth] == 0)
> +			break;
> +		bp = (unsigned long *) bp[0];
> +	}
> +
> +	walking = 0;
> +	return depth;
> +}
> diff --git a/x86/Makefile.common b/x86/Makefile.common
> index 3a14fea..ca80367 100644
> --- a/x86/Makefile.common
> +++ b/x86/Makefile.common
> @@ -12,6 +12,7 @@ cflatobjs += lib/x86/atomic.o
>  cflatobjs += lib/x86/desc.o
>  cflatobjs += lib/x86/isr.o
>  cflatobjs += lib/x86/acpi.o
> +cflatobjs += lib/x86/stack.o
>  
>  $(libcflat): LDFLAGS += -nostdlib
>  $(libcflat): CFLAGS += -ffreestanding -I lib
> @@ -19,6 +20,9 @@ $(libcflat): CFLAGS += -ffreestanding -I lib
>  CFLAGS += -m$(bits)
>  CFLAGS += -O1
>  
> +# dump_stack.o relies on frame pointers.
> +KEEP_FRAME_POINTER := y
> +
>  libgcc := $(shell $(CC) -m$(bits) --print-libgcc-file-name)
>  
>  FLATLIBS = lib/libcflat.a $(libgcc)
> -- 
> 2.7.0.rc3.207.g0ac5344
> 
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Thanks,
drew