diff mbox

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

Message ID 757ca48dec7f6c497948468cb1da89ff646f2e28.1457372594.git.pfeiner@google.com (mailing list archive)
State New, archived
Headers show

Commit Message

Peter Feiner March 7, 2016, 5:46 p.m. UTC 
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

Comments

Andrew Jones March 8, 2016, 4:24 a.m. UTC | #1 
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
> 
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Thanks,
drew

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Peter Feiner March 11, 2016, 12:31 a.m. UTC | #2 
On Tue, Mar 08, 2016 at 11:24:45AM +0700, Andrew Jones wrote:
> On Mon, Mar 07, 2016 at 09:46:53AM -0800, Peter Feiner wrote:
> > +#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?

Right and right. In v6 dump_stack now does the skipping.


> 
> 
> > +	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.

Agreed. Changed in v6.

Peter
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diff mbox

Patch

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