On 20/11/2020 10:49, Martin Liška wrote:
On 11/20/20 10:25 AM, Sebastian Huber wrote:
On 20/11/2020 09:37, Martin Liška wrote:
On 11/17/20 10:57 AM, Sebastian Huber wrote:
This is a proposal to get the gcda data for a gcda info in a
free-standing
environment. It is intended to be used with the
-fprofile-info-section option.
A crude test program which doesn't use a linker script is:
Hello.
I'm not pretty sure how this set up is going to work. Can you please
explain me that?
I was thinking about your needs and I can imagine various techniques
how to generate
gcda files format:
1) embedded system can override fopen, fwrite, fseek to a functions
that do a remote
write-related functions
Yes, this is one option, however, the inhibit_libc disables quite a
lot of libgcov functionality if Newlib is used for example.
I see. Btw do you have available Newlib in the embedded environment?
If so, what I/O functionality is provided?
Yes, I use Newlib with the RTEMS real-time operating system. Newlib
provides the standard C library I/O functions (fopen, etc.). However,
having Newlib available doesn't mean that every application uses its.
Applications are statically linked with the operating system and Newlib.
They only use what is required. Some applications cannot use the
standard C library I/O since they use a lot of infrastructure and
memory. You can do a lot of things with just a couple of KiBs available.
2) - use -fprofile-info-section
- run an app on an embedded system and do a memory dump to a
terminal/console
- take the memory dump to a host system (with IO), run
__gcov_init_from_memory_dump (...)
and then do a normal __gcov_dump
I am not sure if a plain memory dump really simplifies things. You
have to get the filename separately since it is only referenced in
gcov_info and not included in the structure:
struct gcov_info
{
[...]
const char *filename; /* output file name */
[...]
#ifndef IN_GCOV_TOOL
const struct gcov_fn_info *const *functions; /* pointer to pointers
to function
information */
[...]
#endif /* !IN_GCOV_TOOL */
};
I see!
Also the gcov_fn_info is not embedded in the gcov_info structure. If
you do a plain memory dump, then you dump also pointers and how do
you deal with these pointers on the host? You would need some extra
information to describe the memory dump. So, why not use the gcda
format for this? It is also more compact since zero value counters
are skipped. Serial lines are slow, so less data to transfer is good.
/* Convert the gcov information to a gcda data stream. The first
callback is
called exactly once with the filename associated with the gcov
information.
The filename may be NULL. Afterwards, the second callback is
subsequently
called with chunks (the begin and length of the chunk are passed
as the
first two arguments) of the gcda data stream. The fourth
parameter is a
user-provided argument passed as the last argument to the callback
functions. */
extern void __gcov_info_to_gcda (const struct gcov_info *gi_ptr,
void (*filename) (const char *name, void *arg),
void (*dump) (const void *begin, unsigned size,
void *arg),
void *arg);
If __gcov_info_to_gcda() is correctly implemented, then this should
give you directly gcda files if you use something like this:
#include <gcov.h>
#include <stdio.h>
extern const struct gcov_info *__gcov_info_start[];
extern const struct gcov_info *__gcov_info_end[];
static void
filename (const char *f, void *arg)
{
FILE **file = arg;
*file = fopen(f, "rb");
}
static void
dump (const void *d, unsigned n, void *arg)
{
FILE **file = arg;
fwrite(d, n, 1, *file);
}
static void
dump_gcov_info (void)
{
const struct gcov_info **info = __gcov_info_start;
const struct gcov_info **end = __gcov_info_end;
/* Obfuscate variable to prevent compiler optimizations. */
__asm__ ("" : "+r" (end));
while (info != end)
{
FILE *file = NULL;
__gcov_info_to_gcda (*info, filename, dump, &file);
fclose(file);
++info;
}
}
int
main()
{
dump_gcov_info();
return 0;
}
The callback functions give the user the full control how the data of
the gcda file is encoded for the transfer to a host. No gcov
internals are exposed.
All right. Btw. how will you implement these 2 callbacks on the
embedded target?
One options is to convert the gcov info to YAML:
gcov-info:
- file: filename1
data: <... base64 encoded data from __gcov_info_to_gcda ... >
- file: filename2
data: ...
Then send the data to the host via a serial line. On the host read the
data, parse the YAML, and create the gcda files. The
__gcov_info_to_gcda() needs about 408 bytes of ARM Thumb-2 code and no
data. You need a polled character output function, the linker set
iteration and two callbacks. So, you can easily dump the gcov
information with about 1KiB of code and no data except a small stack.
Apart from these 2 hooks, I bet you will also need gcov_position and
gcov_seek functions,
can be seen in my sent patch.
For what do I need them?
--
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