[PATCH v4] selftest: size: Add size test for Linux kernel

[PATCH v4] selftest: size: Add size test for Linux kernel

[Tim Bird]

This test shows the amount of memory used by the system.
Note that this is dependent on the user-space that is loaded
when this program runs.  Optimally, this program would be
run as the init program itself.

The program is optimized for size itself, to avoid conflating
its own execution with that of the system software.
The code is compiled statically, with no stdlibs. On my x86_64 system,
this results in a statically linked binary of less than 5K.

Signed-off-by: Tim Bird <tim.bird-/MT0OVThwyLZJqsBc5GL+g@public.gmane.org>
---
Changes from v3:
  - fix copyright string (again!)
  - use __builtin_strlen instead of my own strlen
  - replace main with _start
  - add more human-readable output
  - put libgcc reference into a variable in Makefile

Changes from v2:
  - add return values to print routines
  - add .gitignore file

Changes from v1:
  - use more correct Copyright string in get_size.c

 tools/testing/selftests/Makefile        |   1 +
 tools/testing/selftests/size/.gitignore |   1 +
 tools/testing/selftests/size/Makefile   |  23 +++++++
 tools/testing/selftests/size/get_size.c | 111 ++++++++++++++++++++++++++++++++
 4 files changed, 136 insertions(+)
 create mode 100644 tools/testing/selftests/size/.gitignore
 create mode 100644 tools/testing/selftests/size/Makefile
 create mode 100644 tools/testing/selftests/size/get_size.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 45f145c..fa91aef 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -15,6 +15,7 @@ TARGETS += user
 TARGETS += sysctl
 TARGETS += firmware
 TARGETS += ftrace
+TARGETS += size
 
 TARGETS_HOTPLUG = cpu-hotplug
 TARGETS_HOTPLUG += memory-hotplug
diff --git a/tools/testing/selftests/size/.gitignore b/tools/testing/selftests/size/.gitignore
new file mode 100644
index 0000000..189b781
--- /dev/null
+++ b/tools/testing/selftests/size/.gitignore
@@ -0,0 +1 @@
+get_size
diff --git a/tools/testing/selftests/size/Makefile b/tools/testing/selftests/size/Makefile
new file mode 100644
index 0000000..1862786
--- /dev/null
+++ b/tools/testing/selftests/size/Makefile
@@ -0,0 +1,23 @@
+#ifndef CC
+	CC = $(CROSS_COMPILE)gcc
+#endif
+
+#ifndef STRIP
+	STRIP = $(CROSS_COMPILE)strip
+#endif
+
+all: get_size
+
+LIBGCC=$(shell $(CC) -print-libgcc-file-name)
+
+get_size: get_size.c
+	$(CC) --static -ffreestanding -nostartfiles \
+		-Wl,--entry=_start get_size.c $(LIBGCC) \
+		-o get_size
+	$(STRIP) -s get_size
+
+run_tests: all
+	./get_size
+
+clean:
+	$(RM) get_size
diff --git a/tools/testing/selftests/size/get_size.c b/tools/testing/selftests/size/get_size.c
new file mode 100644
index 0000000..7e9bbb4
--- /dev/null
+++ b/tools/testing/selftests/size/get_size.c
@@ -0,0 +1,111 @@
+/*
+ * Copyright 2014 Sony Mobile Communications Inc.
+ *
+ * Licensed under the terms of the GNU GPL License version 2
+ *
+ * Selftest for runtime system size
+ *
+ * Prints the amount of RAM that the currently running system is using.
+ *
+ * This program tries to be as small as possible itself, to
+ * avoid perturbing the system memory utilization with its
+ * own execution.  It also attempts to have as few dependencies
+ * on kernel features as possible.
+ *
+ * It should be statically linked, with startup libs avoided.
+ * It uses no library calls, and only the following 3 syscalls:
+ *   sysinfo(), write(), and _exit()
+ *
+ * For output, it avoids printf (which in some C libraries
+ * has large external dependencies) by  implementing it's own
+ * number output and print routines, and using __builtin_strlen()
+ */
+
+#include <sys/sysinfo.h>
+#include <unistd.h>
+
+#define STDOUT_FILENO 1
+
+int print(const char *s)
+{
+	return write(STDOUT_FILENO, s, __builtin_strlen(s));
+}
+
+
+/*
+ * num_to_str - put digits from num into *s, left to right
+ *   do this by dividing the number by powers of 10
+ *   the tricky part is to omit leading zeros
+ *   don't print zeros until we've started printing any numbers at all
+ */
+void num_to_str(unsigned long num, char *s)
+{
+	unsigned long long temp, div;
+	int started;
+
+	temp = num;
+	div = 1000000000000000000LL;
+	started = 0;
+	while (div) {
+		if (temp/div || started) {
+			*s++ = (unsigned char)(temp/div + '0');
+			started = 1;
+		}
+		temp -= (temp/div)*div;
+		div /= 10;
+	}
+	*s = 0;
+}
+
+int print_num(unsigned long num)
+{
+	char num_buf[30];
+
+	num_to_str(num, num_buf);
+	return print(num_buf);
+}
+
+int print_k_value(const char *s, unsigned long num, unsigned long units)
+{
+	unsigned long long temp;
+	int ccode;
+
+	print(s);
+
+	temp = num;
+	temp = (temp * units)/1024;
+	num = temp;
+	ccode = print_num(num);
+	print("\n");
+	return ccode;
+}
+
+/* this program has no main(), as startup libraries are not used */
+void _start(void)
+{
+	int ccode;
+	struct sysinfo info;
+	unsigned long used;
+
+	print("Testing system size.\n");
+	print("1..1\n");
+
+	ccode = sysinfo(&info);
+	if (ccode < 0) {
+		print("not ok 1 get size runtime size\n");
+		print("# could not get sysinfo\n");
+		_exit(ccode);
+	}
+	/* ignore cache complexities for now */
+	used = info.totalram - info.freeram - info.bufferram;
+	print_k_value("ok 1 get runtime memory use # size = ", used,
+		info.mem_unit);
+
+	print("# System runtime memory report (units in Kilobytes):\n");
+	print_k_value("#   Total:  ", info.totalram, info.mem_unit);
+	print_k_value("#   Free:   ", info.freeram, info.mem_unit);
+	print_k_value("#   Buffer: ", info.bufferram, info.mem_unit);
+	print_k_value("#   In use: ", used, info.mem_unit);
+
+	_exit(0);
+}
-- 
1.8.2.2

Re: [PATCH v4] selftest: size: Add size test for Linux kernel

[Josh Triplett]

On Wed, Nov 26, 2014 at 08:27:23PM -0800, Tim Bird wrote:
> --- /dev/null
> +++ b/tools/testing/selftests/size/Makefile
[...]
> +LIBGCC=$(shell $(CC) -print-libgcc-file-name)
> +
> +get_size: get_size.c
> +	$(CC) --static -ffreestanding -nostartfiles \
> +		-Wl,--entry=_start get_size.c $(LIBGCC) \
> +		-o get_size

You don't need -Wl,--entry=_start; that's the default.

You shouldn't need to manually find libgcc, either; the compiler should
do that for you.  What goes wrong if you don't include that?  If you're
trying to link libgcc statically, try -static-libgcc.

Also, static is normally spelled -static, not --static.

> --- /dev/null
> +++ b/tools/testing/selftests/size/get_size.c
[...]
> +int print(const char *s)

This function, and all the others apart from _start, should be declared
static.

> +void num_to_str(unsigned long num, char *s)

Likewise, static.

> +{
> +	unsigned long long temp, div;
> +	int started;
> +
> +	temp = num;
> +	div = 1000000000000000000LL;
> +	started = 0;
> +	while (div) {
> +		if (temp/div || started) {
> +			*s++ = (unsigned char)(temp/div + '0');
> +			started = 1;
> +		}
> +		temp -= (temp/div)*div;
> +		div /= 10;
> +	}
> +	*s = 0;
> +}

You'd probably end up with significantly smaller code (and no divisions,
and thus no corner cases on architectures that need a special function
to do unsigned long long division) if you print in hex.  You could also
drop the "no leading zeros" logic, and just *always* print a 64-bit
value as 16 hex digits.

> +int print_num(unsigned long num)

Likewise, static.

> +{
> +	char num_buf[30];
> +
> +	num_to_str(num, num_buf);
> +	return print(num_buf);
> +}
> +
> +int print_k_value(const char *s, unsigned long num, unsigned long units)
> +{
> +	unsigned long long temp;
> +	int ccode;
> +
> +	print(s);
> +
> +	temp = num;
> +	temp = (temp * units)/1024;
> +	num = temp;
> +	ccode = print_num(num);
> +	print("\n");
> +	return ccode;
> +}

I'd suggest dropping this entirely, and just always printing the exact
values returned by sysinfo.  Drop the multiply, too, and just print
info.mem_unit as well.  It's easy to post-process the value in a more
capable environment.

> +/* this program has no main(), as startup libraries are not used */
> +void _start(void)
> +{
> +	int ccode;
> +	struct sysinfo info;
> +	unsigned long used;
> +
> +	print("Testing system size.\n");
> +	print("1..1\n");
> +
> +	ccode = sysinfo(&info);
> +	if (ccode < 0) {
> +		print("not ok 1 get size runtime size\n");

Shouldn't the "not ok" here and the "ok" below have the same test
description?

> +		print("# could not get sysinfo\n");
> +		_exit(ccode);
> +	}
> +	/* ignore cache complexities for now */
> +	used = info.totalram - info.freeram - info.bufferram;
> +	print_k_value("ok 1 get runtime memory use # size = ", used,
> +		info.mem_unit);
> +
> +	print("# System runtime memory report (units in Kilobytes):\n");
> +	print_k_value("#   Total:  ", info.totalram, info.mem_unit);
> +	print_k_value("#   Free:   ", info.freeram, info.mem_unit);
> +	print_k_value("#   Buffer: ", info.bufferram, info.mem_unit);
> +	print_k_value("#   In use: ", used, info.mem_unit);
> +
> +	_exit(0);
> +}
> -- 
> 1.8.2.2
> 

Re: [PATCH v4] selftest: size: Add size test for Linux kernel

[Tim Bird]

On 11/26/2014 10:04 PM, Josh Triplett wrote:
> On Wed, Nov 26, 2014 at 08:27:23PM -0800, Tim Bird wrote:
>> --- /dev/null
>> +++ b/tools/testing/selftests/size/Makefile
> [...]
>> +LIBGCC=$(shell $(CC) -print-libgcc-file-name)
>> +
>> +get_size: get_size.c
>> +	$(CC) --static -ffreestanding -nostartfiles \
>> +		-Wl,--entry=_start get_size.c $(LIBGCC) \
>> +		-o get_size
> 
> You don't need -Wl,--entry=_start; that's the default.
OK - it works without this.  Thanks.

> You shouldn't need to manually find libgcc, either; the compiler should
> do that for you.  What goes wrong if you don't include that?  If you're
> trying to link libgcc statically, try -static-libgcc.
> 
> Also, static is normally spelled -static, not --static.

Hmm.  Not sure where I got --static from, but it worked.
But if -static is the norm I'm fine changing to that.

Upon experimentation, I don't need the explicit libgcc or for that
matter the -static-libgcc either.

>> --- /dev/null
>> +++ b/tools/testing/selftests/size/get_size.c
> [...]
>> +int print(const char *s)
> 
> This function, and all the others apart from _start, should be declared
> static.

OK will do.

>> +void num_to_str(unsigned long num, char *s)
> 
> Likewise, static.
OK

>> +{
>> +	unsigned long long temp, div;
>> +	int started;
>> +
>> +	temp = num;
>> +	div = 1000000000000000000LL;
>> +	started = 0;
>> +	while (div) {
>> +		if (temp/div || started) {
>> +			*s++ = (unsigned char)(temp/div + '0');
>> +			started = 1;
>> +		}
>> +		temp -= (temp/div)*div;
>> +		div /= 10;
>> +	}
>> +	*s = 0;
>> +}
> 
> You'd probably end up with significantly smaller code (and no divisions,
> and thus no corner cases on architectures that need a special function
> to do unsigned long long division) if you print in hex.  You could also
> drop the "no leading zeros" logic, and just *always* print a 64-bit
> value as 16 hex digits.

I'd like to keep base-10 output.  As far as size is concerned, the
code is now at well under 2 pages (8k), which is much smaller than
any actually useful program.  The only noticeable change in size would
be if I got it under 4096, but I don't want to sacrifice too many
features to get there (as that's still only 1 page difference in
memory usage.)

BTW - using sstrip, I can get it to 4096 already, as is.

Unfortunately, 'sstrip -z', which gets it to 2061, makes
it not work.  I need to check out what the problem is there.
Also, the ELF file still has an unneeded note section.  I think
easier reductions, without sacrificing functionality, are available
by tweaking the ELF header (ie fixing sstrip, for those that
want to use it).
 
>> +int print_num(unsigned long num)
> 
> Likewise, static.

OK

>> +{
>> +	char num_buf[30];
>> +
>> +	num_to_str(num, num_buf);
>> +	return print(num_buf);
>> +}
>> +
>> +int print_k_value(const char *s, unsigned long num, unsigned long units)
>> +{
>> +	unsigned long long temp;
>> +	int ccode;
>> +
>> +	print(s);
>> +
>> +	temp = num;
>> +	temp = (temp * units)/1024;
>> +	num = temp;
>> +	ccode = print_num(num);
>> +	print("\n");
>> +	return ccode;
>> +}
> 
> I'd suggest dropping this entirely, and just always printing the exact
> values returned by sysinfo.  Drop the multiply, too, and just print
> info.mem_unit as well.  It's easy to post-process the value in a more
> capable environment.

I'd prefer to keep the output easily human-readable.
 
>> +/* this program has no main(), as startup libraries are not used */
>> +void _start(void)
>> +{
>> +	int ccode;
>> +	struct sysinfo info;
>> +	unsigned long used;
>> +
>> +	print("Testing system size.\n");
>> +	print("1..1\n");
>> +
>> +	ccode = sysinfo(&info);
>> +	if (ccode < 0) {
>> +		print("not ok 1 get size runtime size\n");
> 
> Shouldn't the "not ok" here and the "ok" below have the same test
> description?
Yes.  Thanks.  Good catch.
 
>> +		print("# could not get sysinfo\n");
>> +		_exit(ccode);
>> +	}
>> +	/* ignore cache complexities for now */
>> +	used = info.totalram - info.freeram - info.bufferram;
>> +	print_k_value("ok 1 get runtime memory use # size = ", used,
>> +		info.mem_unit);
>> +
>> +	print("# System runtime memory report (units in Kilobytes):\n");
>> +	print_k_value("#   Total:  ", info.totalram, info.mem_unit);
>> +	print_k_value("#   Free:   ", info.freeram, info.mem_unit);
>> +	print_k_value("#   Buffer: ", info.bufferram, info.mem_unit);
>> +	print_k_value("#   In use: ", used, info.mem_unit);
>> +
>> +	_exit(0);
>> +}
>> -- 
>> 1.8.2.2

OK - look for a new version shortly (maybe not today, though).
 -- Tim