Re: [RFC PATCH 2/4] gcov: add support for gcc 4.7 gcov format
From: Peter Oberparleiter
Date: Mon Aug 26 2013 - 08:45:21 EST
On 23.08.2013 23:00, Frantisek Hrbata wrote:
> On Fri, Aug 23, 2013 at 05:12:19PM +0200, Peter Oberparleiter wrote:
>> On 23.08.2013 10:39, Frantisek Hrbata wrote:
>>> The gcov in-memory format changed in gcc 4.7. The biggest change, which
>>> requires this special implementation, is that gcov_info no longer contains
>>> array of counters for each counter type for all functions and gcov_fn_info is
>>> not used for mapping of function's counters to these arrays(offset). Now each
>>> gcov_fn_info contans it's counters, which makes things a little bit easier.
>>
>> By now I've come to the conclusion that I may have over-engineered
>> gcov_iter_next in the original GCC 3.4 implementation. This became especially
>> apparent when someone tried to adjust that code to also work with a specific
>> android GCC version - adding a simple field to the output file format required
>> major complex changes.
>>
>> Therefore in my version of the GCC 4.7 support, I opted to replace this logic
>> with the simpler approach of generating the gcov data file in-memory during
>> open (gcov_iter_new) and reducing gcov_iter_next/gcov_iter_write to simple
>> copy-from-buffer functions.
>
> Yes, this seems reasonable and much easier approach to me, but we will end up
> with three copies of one gcov(gcda) file data in memory: data from gcc, our
> buffer and the buffer in seq file. But I guess this is not a big problem,
> unless someone opens a huge amount of gcda files in parallel. Generally I
> like this idea. This will be also probably faster then writing 1 or 2 ints per
> one iter write.
You're right about the data being in multiple buffers for the time that a .gcda
file is opened, but as you mentioned, this shouldn't be a problem since usually
only one .gcda file is open at a time. Also the reduction in code complexity is
in my opinion well worth it.
>> Since I can see the need to change the format code again in the future,
>> I think it would be easier to simplify this part of the code correspondingly.
>> I'm adding my version of this part of the implementation as discussion input
>> below (the relevant part starts at convert_to_gcda()).
>
> I have really only two nits to the code(please see below). I spent some time
> checking the new seq/iter implementation and it seems ok to me. Generally I like
> how simple this change is done.
>
>>
>> ---
>> kernel: gcov: add support for gcc 4.7 gcov format
>>
>> GCC 4.7 changed the format of gcov related data structures, both
>> on-disk and in memory. Add support for the new format.
>>
>> Signed-off-by: Peter Oberparleiter <oberpar@xxxxxxxxxxxxxxxxxx>
>> ---
>> kernel/gcov/Makefile | 4
>> kernel/gcov/gcc_4_7.c | 510 ++++++++++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 513 insertions(+), 1 deletion(-)
>>
>> --- a/kernel/gcov/Makefile
>> +++ b/kernel/gcov/Makefile
>> @@ -1,3 +1,5 @@
>> ccflags-y := -DSRCTREE='"$(srctree)"' -DOBJTREE='"$(objtree)"'
>>
>> -obj-$(CONFIG_GCOV_KERNEL) := base.o fs.o gcc_3_4.o
>> +obj-$(CONFIG_GCOV_KERNEL) := base.o fs.o
>> +obj-$(CONFIG_GCOV_KERNEL) += $(call cc-ifversion, -lt, 0407, gcc_3_4.o)
>> +obj-$(CONFIG_GCOV_KERNEL) += $(call cc-ifversion, -ge, 0407, gcc_4_7.o)
>> --- /dev/null
>> +++ b/kernel/gcov/gcc_4_7.c
>> @@ -0,0 +1,510 @@
>> +/*
>> + * This code provides functions to handle gcc's profiling data format
>> + * introduced with gcc 4.7. Future versions of gcc may change the gcov
>> + * format (as happened before), so all format-specific information needs
>> + * to be kept modular and easily exchangeable.
>> + *
>> + * This file is based on gcc-internal definitions. Functions and data
>> + * structures are defined to be compatible with gcc counterparts.
>> + * For a better understanding, refer to gcc source: gcc/gcov-io.h.
>> + *
>> + * Copyright IBM Corp. 2013
>> + * Author(s): Peter Oberparleiter <oberpar@xxxxxxxxxxxxxxxxxx>
>> + *
>> + * Uses gcc-internal data definitions.
>> + */
>> +
>> +#include <linux/errno.h>
>> +#include <linux/slab.h>
>> +#include <linux/string.h>
>> +#include <linux/seq_file.h>
>> +#include <linux/vmalloc.h>
>> +#include <linux/types.h>
>> +#include "gcov.h"
>> +
>> +/*
>> + * Profiling data types used for gcc 4.7 and above - these are defined by
>> + * gcc and need to be kept as close to the original definition as possible to
>> + * remain compatible.
>> + */
>> +#define GCOV_COUNTERS 8
>> +#define GCOV_DATA_MAGIC ((unsigned int) 0x67636461)
>> +#define GCOV_TAG_FUNCTION ((unsigned int) 0x01000000)
>> +#define GCOV_TAG_COUNTER_BASE ((unsigned int) 0x01a10000)
>> +#define GCOV_TAG_FOR_COUNTER(count) \
>> + (GCOV_TAG_COUNTER_BASE + ((unsigned int) (count) << 17))
>> +
>> +#if BITS_PER_LONG >= 64
>> +typedef long gcov_type;
>> +#else
>> +typedef long long gcov_type;
>> +#endif
>> +
>> +/**
>> + * struct gcov_ctr_info - profiling data per function and counter type
>> + * @num: number of counter values for this type
>> + * @values: array of counter values for this type
>> + *
>> + * This data is generated by gcc during compilation and doesn't change
>> + * at run-time with the exception of the values array.
>> + */
>> +struct gcov_ctr_info {
>> + unsigned int num;
>> + gcov_type *values;
>> +};
>> +
>> +/**
>> + * struct gcov_fn_info - profiling meta data per function
>> + * @key: comdat key
>> + * @ident: object file-unique function identifier
>> + * @lineno_checksum: function lineno_checksum
>> + * @cfg_checksum: function cfg_checksum
>> + * @ctrs: counters
>> + *
>> + * This data is generated by gcc during compilation and doesn't change
>> + * at run-time.
>> + */
>> +struct gcov_fn_info {
>> + const struct gcov_info *key;
>> + unsigned int ident;
>> + unsigned int lineno_checksum;
>> + unsigned int cfg_checksum;
>> + struct gcov_ctr_info ctrs[0];
>> +};
>> +
>> +typedef void (*gcov_merge_fn)(gcov_type *, unsigned int);
>> +
>> +/**
>> + * struct gcov_info - profiling data per object file
>> + * @version: gcov version magic indicating the gcc version used for compilation
>> + * @next: list head for a singly-linked list
>> + * @stamp: time stamp
>> + * @filename: name of the associated gcov data file
>> + * @merge: functions for merging counts per counter type or null for unused
>> + * @n_functions: number of instrumented functions
>> + * @functions: function data
>> + *
>> + * This data is generated by gcc during compilation and doesn't change
>> + * at run-time with the exception of the next pointer.
>> + */
>> +struct gcov_info {
>> + unsigned int version;
>> + struct gcov_info *next;
>> + unsigned int stamp;
>> + const char *filename;
>> + gcov_merge_fn merge[GCOV_COUNTERS];
>> + unsigned int n_functions;
>> + struct gcov_fn_info **functions;
>
> I can see that you removed the const part. I was thinking about it too, because
> it requires ugly cast-const-away code in the gcov_info_dup and it is imho not
> necessary, but I left the original definition from gcc anyway.
The kernel's usage of gcov_info is slightly different from the GCC's internal
one, so a slight divergence should be ok from my point of view, especially
considering that the outcome (dropping a const declaration) is the same.
>
>> +};
>> +
>> +/* Symbolic links to be created for each profiling data file. */
>> +const struct gcov_link gcov_link[] = {
>> + { OBJ_TREE, "gcno" }, /* Link to .gcno file in $(objtree). */
>> + { 0, NULL},
>> +};
>> +
>> +/*
>> + * Determine whether a counter is active. Based on gcc magic. Doesn't change
>> + * at run-time.
>> + */
>> +static int counter_active(struct gcov_info *info, unsigned int type)
>> +{
>> + return info->merge[type] != NULL;
>> +}
>> +
>> +/* Determine number of active counters. Based on gcc magic. */
>> +static unsigned int num_counter_active(struct gcov_info *info)
>> +{
>> + unsigned int i;
>> + unsigned int result = 0;
>> +
>> + for (i = 0; i < GCOV_COUNTERS; i++) {
>> + if (counter_active(info, i))
>> + result++;
>> + }
>> + return result;
>> +}
>> +
>> +/**
>> + * gcov_info_reset - reset profiling data to zero
>> + * @info: profiling data set
>> + */
>> +void gcov_info_reset(struct gcov_info *info)
>> +{
>> + unsigned int active = num_counter_active(info);
>> + unsigned int f, i;
>> + struct gcov_ctr_info *ctr;
>> +
>> + for (f = 0; f < info->n_functions; f++) {
>> + for (i = 0; i < active; i++) {
>> + ctr = &info->functions[f]->ctrs[i];
>> + memset(ctr->values, 0, ctr->num * sizeof(gcov_type));
>> + }
>> + }
>> +}
>> +
>> +/**
>> + * gcov_info_is_compatible - check if profiling data can be added
>> + * @info1: first profiling data set
>> + * @info2: second profiling data set
>> + *
>> + * Returns non-zero if profiling data can be added, zero otherwise.
>> + */
>> +int gcov_info_is_compatible(struct gcov_info *info1, struct gcov_info *info2)
>> +{
>> + return (info1->stamp == info2->stamp);
>> +}
>> +
>> +/**
>> + * gcov_info_add - add up profiling data
>> + * @dest: profiling data set to which data is added
>> + * @source: profiling data set which is added
>> + *
>> + * Adds profiling counts of @source to @dest.
>> + */
>> +void gcov_info_add(struct gcov_info *dest, struct gcov_info *source)
>> +{
>> + unsigned int active = num_counter_active(dest);
>> + unsigned int f, i, j;
>> +
>> + for (f = 0; f < dest->n_functions; f++) {
>> + for (i = 0; i < active; i++) {
>> + struct gcov_ctr_info *d_ctr =
>> + &dest->functions[f]->ctrs[i];
>> + struct gcov_ctr_info *s_ctr =
>> + &source->functions[f]->ctrs[i];
>> +
>> + for (j = 0; j < d_ctr->num; j++) {
>> + d_ctr->values[j] += s_ctr->values[j];
>> + }
>> + }
>> + }
>> +}
>> +
>> +/**
>> + * gcov_info_dup - duplicate profiling data set
>> + * @info: profiling data set to duplicate
>> + *
>> + * Return newly allocated duplicate on success, %NULL on error.
>> + */
>> +struct gcov_info *gcov_info_dup(struct gcov_info *info)
>> +{
>> + struct gcov_info *dup;
>> + unsigned int active = num_counter_active(info);
>> + unsigned int i, j;
>> +
>> + /* Duplicate gcov_info. */
>> + dup = kzalloc(sizeof(struct gcov_info), GFP_KERNEL);
>> + if (!dup)
>> + return NULL;
>> + dup->version = info->version;
>> + dup->stamp = info->stamp;
>> + dup->n_functions = info->n_functions;
>> + memcpy(dup->merge, info->merge, sizeof(dup->merge));
>> + /* Duplicate filename. */
>> + dup->filename = kstrdup(info->filename, GFP_KERNEL);
>> + if (!dup->filename)
>> + goto err_free;
>> + /* Duplicate table of functions. */
>> + dup->functions = kzalloc(sizeof(struct gcov_fn_info *) *
>> + info->n_functions, GFP_KERNEL);
>> + if (!dup->functions)
>> + goto err_free;
>> + for (i = 0; i < info->n_functions; i++) {
>> + struct gcov_fn_info *src_fn = info->functions[i];
>> + struct gcov_fn_info *dest_fn;
>> +
>> + /* Duplicate gcov_fn_info. */
>> + dup->functions[i] = kzalloc(sizeof(struct gcov_fn_info) +
>> + sizeof(struct gcov_ctr_info) *
>> + active, GFP_KERNEL);
>> + if (!dup->functions[i])
>> + goto err_free;
>> + dest_fn = dup->functions[i];
>> + dest_fn->ident = src_fn->ident;
>> + dest_fn->lineno_checksum = src_fn->lineno_checksum;
>> + dest_fn->cfg_checksum = src_fn->cfg_checksum;
>> +
>> + for (j = 0; j < active; j++) {
>> + struct gcov_ctr_info *src_ctr = &src_fn->ctrs[j];
>> + struct gcov_ctr_info *dest_ctr = &dest_fn->ctrs[j];
>> + size_t size = sizeof(gcov_type) * src_ctr->num;
>> +
>> + /* Duplicate gcov_ctr_info. */
>> + dest_ctr->num = src_ctr->num;
>> + dest_ctr->values = vmalloc(size);
> ^^^^^^^
> Does the vmalloc make sense here? The counters are allocated per function, so I
> expect they will be pretty small compared when there was one "huge" array for
> each counter type for all functions per gcov_info. Meaning here we will not
> consume a "big" continuous block of phys memory. I'm just currious and maybe I'm
> missing something. Anyway this is just a nit.
Good point. Previously the sizes to be allocated here could be as large as 64k.
Now the largest I see for 3.10 on an s390x system is ~3k. On the other hand
since we're not on a performance critical path, staying with vmalloc might just
be safer.
>> + if (!dest_ctr->values)
>> + goto err_free;
>> + memcpy(dest_ctr->values, src_ctr->values, size);
>> + }
>> + }
>> + return dup;
>> +
>> +err_free:
>> + gcov_info_free(dup);
>> + return NULL;
>> +}
>> +
>> +/**
>> + * gcov_info_free - release memory for profiling data set duplicate
>> + * @info: profiling data set duplicate to free
>> + */
>> +void gcov_info_free(struct gcov_info *info)
>> +{
>> + unsigned int active = num_counter_active(info);
>> + unsigned int i, j;
>> +
>> + if (info->functions) {
>> + for (i = 0; i < info->n_functions; i++) {
>> + if (!info->functions[i])
>> + continue;
>> + for (j = 0; j < active; j++)
>> + vfree(info->functions[i]->ctrs[j].values);
>> + kfree(info->functions[i]);
>> + }
>> + }
>> + kfree(info->functions);
>> + kfree(info->filename);
>> + kfree(info);
>> +}
>> +
>> +#define ITER_STRIDE PAGE_SIZE
>> +
>> +/**
>> + * struct gcov_iterator - specifies current file position in logical records
>> + * @buffer: buffer containing file data
>> + * @size: size of buffer
>> + * @pos: current position in file
>> + */
>> +struct gcov_iterator {
>> + struct gcov_info *info;
>> + void *buffer;
>> + size_t size;
>> + loff_t pos;
>> +};
>> +
>> +/**
>> + * store_gcov_u32 - store 32 bit number in gcov format to buffer
>> + * @buffer: target buffer or NULL
>> + * @off: offset into the buffer
>> + * @v: value to be stored
>> + *
>> + * Number format defined by gcc: numbers are recorded in the 32 bit
>> + * unsigned binary form of the endianness of the machine generating the
>> + * file. Returns the number of bytes stored. If @buffer is %NULL, doesn't
>> + * store anything.
>> + */
>> +static size_t store_gcov_u32(void *buffer, size_t off, u32 v)
>> +{
>> + u32 *data;
>> +
>> + if (buffer) {
>> + data = buffer + off;
>> + *data = v;
>> + }
>> +
>> + return sizeof(*data);
>> +}
>> +
>> +/**
>> + * store_gcov_u64 - store 64 bit number in gcov format to buffer
>> + * @buffer: target buffer or NULL
>> + * @off: offset into the buffer
>> + * @v: value to be stored
>> + *
>> + * Number format defined by gcc: numbers are recorded in the 32 bit
>> + * unsigned binary form of the endianness of the machine generating the
>> + * file. 64 bit numbers are stored as two 32 bit numbers, the low part
>> + * first. Returns the number of bytes stored. If @buffer is %NULL, doesn't store
>> + * anything.
>> + */
>> +static size_t store_gcov_u64(void *buffer, size_t off, u64 v)
>> +{
>> + u32 *data;
>> +
>> + if (buffer) {
>> + data = buffer + off;
>> +
>> + data[0] = (v & 0xffffffffUL);
>> + data[1] = (v >> 32);
>> + }
>> +
>> + return sizeof(*data) * 2;
>> +}
>> +
>> +/**
>> + * get_ctr_type - return type of specified counter
>> + * @info: profiling data set
>> + * @num: index into list of active counters
>> + *
>> + * Returns the type of the specified counter.
>> + */
>> +static int get_ctr_type(struct gcov_info *info, unsigned int num)
>> +{
>> + unsigned int type;
>> +
>> + for (type = 0; type < GCOV_COUNTERS; type++) {
>> + if (counter_active(info, type)) {
>> + if (num == 0)
>> + break;
>> + num--;
>> + }
>> + }
>> +
>> + return type;
>> +}
>> +
>> +/**
>> + * convert_to_gcda - convert profiling data set to gcda file format
>> + * @buffer: the buffer to store file data or %NULL if no data should be stored
>> + * @info: profiling data set to be converted
>> + *
>> + * Returns the number of bytes that were/would have been stored into the buffer.
>> + */
>> +static size_t convert_to_gcda(char *buffer, struct gcov_info *info)
>> +{
>> + unsigned int active = num_counter_active(info);
>> + unsigned int i, j, k;
>> + size_t pos = 0;
>> +
>> + /* File header. */
>> + pos += store_gcov_u32(buffer, pos, GCOV_DATA_MAGIC);
>> + pos += store_gcov_u32(buffer, pos, info->version);
>> + pos += store_gcov_u32(buffer, pos, info->stamp);
>> +
>> + for (i = 0; i < info->n_functions; i++) {
>> + struct gcov_fn_info *fn = info->functions[i];
>> +
>> + /* Function record. */
>> + pos += store_gcov_u32(buffer, pos, GCOV_TAG_FUNCTION);
>> + pos += store_gcov_u32(buffer, pos, 3);
>> + pos += store_gcov_u32(buffer, pos, fn->ident);
>> + pos += store_gcov_u32(buffer, pos, fn->lineno_checksum);
>> + pos += store_gcov_u32(buffer, pos, fn->cfg_checksum);
>> +
>> + for (j = 0; j < active; j++) {
>> + struct gcov_ctr_info *ctr = &fn->ctrs[j];
>> + int type = get_ctr_type(info, j);
>> +
>> + /* Counter record. */
>> + pos += store_gcov_u32(buffer, pos,
>> + GCOV_TAG_FOR_COUNTER(type));
>> + pos += store_gcov_u32(buffer, pos, ctr->num * 2);
>> +
>> + for (k = 0; k < ctr->num; k++) {
>> + pos += store_gcov_u64(buffer, pos,
>> + ctr->values[k]);
>> + }
>> + }
>> +
>> +
>> + }
>> +
>> + return pos;
>> +}
>> +
>> +/**
>> + * gcov_iter_new - allocate and initialize profiling data iterator
>> + * @info: profiling data set to be iterated
>> + *
>> + * Return file iterator on success, %NULL otherwise.
>> + */
>> +struct gcov_iterator *gcov_iter_new(struct gcov_info *info)
>> +{
>> + struct gcov_iterator *iter;
>> +
>> + iter = kzalloc(sizeof(struct gcov_iterator), GFP_KERNEL);
>> + if (!iter)
>> + goto err_free;
>> +
>> + iter->info = info;
>> + /* Dry-run to get the actual buffer size. */
>> + iter->size = convert_to_gcda(NULL, info);
>> + iter->buffer = vmalloc(iter->size);
>> + if (!iter->buffer)
>> + goto err_free;
>> +
>> + convert_to_gcda(iter->buffer, info);
>> +
>> + return iter;
>> +
>> +err_free:
>> + kfree(iter);
>> + return NULL;
>> +}
>> +
>> +/**
>> + * gcov_iter_free - release memory for iterator
>> + * @iter: file iterator to free
>> + */
>> +void gcov_iter_free(struct gcov_iterator *iter)
>> +{
>> + vfree(iter->buffer);
>> + kfree(iter);
>> +}
>> +
>> +/**
>> + * gcov_iter_get_info - return profiling data set for given file iterator
>> + * @iter: file iterator
>> + */
>> +struct gcov_info *gcov_iter_get_info(struct gcov_iterator *iter)
>> +{
>> + return iter->info;
>> +}
>> +
>> +/**
>> + * gcov_iter_start - reset file iterator to starting position
>> + * @iter: file iterator
>> + */
>> +void gcov_iter_start(struct gcov_iterator *iter)
>> +{
>> + iter->pos = 0;
>> +}
>> +
>> +/**
>> + * gcov_iter_next - advance file iterator to next logical record
>> + * @iter: file iterator
>> + *
>> + * Return zero if new position is valid, non-zero if iterator has reached end.
>> + */
>> +int gcov_iter_next(struct gcov_iterator *iter)
>> +{
>> + if (iter->pos < iter->size)
>> + iter->pos += ITER_STRIDE;
>> + if (iter->pos >= iter->size)
>> + return -EINVAL;
>> +
>> + return 0;
>> +}
>> +
>> +/**
>> + * gcov_iter_write - write data for current pos to seq_file
>> + * @iter: file iterator
>> + * @seq: seq_file handle
>> + *
>> + * Return zero on success, non-zero otherwise.
>> + */
>> +int gcov_iter_write(struct gcov_iterator *iter, struct seq_file *seq)
>> +{
>> + size_t len;
>> +
>> + if (iter->pos >= iter->size)
>> + return -EINVAL;
>> +
>> + len = ITER_STRIDE;
>> + if (iter->pos + len > iter->size)
>> + len = iter->size - iter->pos;
>> +
>> + seq_write(seq, iter->buffer + iter->pos, len);
>> +
>> + return 0;
>> +}
>> +
>> +/**
>> + * gcov_info_get_filename - return name of the associated gcov data file
>> + * @info: profiling data set
>> + */
>> +const char *gcov_info_get_filename(struct gcov_info *info)
>> +{
>> + return info->filename;
>> +}
>>
>> --
>> Peter Oberparleiter
>> Linux on System z Development - IBM Germany
--
Peter Oberparleiter
Linux on System z Development - IBM Germany
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