Documentation/perf_counter/util/symbol.c

#include "util.h"
#include "../perf.h"
#include "string.h"
#include "symbol.h"

#include <libelf.h>
#include <gelf.h>
#include <elf.h>

static struct symbol *symbol__new(uint64_t start, uint64_t len,
				  const char *name, unsigned int priv_size)
{
	size_t namelen = strlen(name) + 1;
	struct symbol *self = malloc(priv_size + sizeof(*self) + namelen);

	if (self != NULL) {
		if (priv_size) {
			memset(self, 0, priv_size);
			self = ((void *)self) + priv_size;
		}
		self->start = start;
		self->end   = start + len - 1;
		memcpy(self->name, name, namelen);
	}

	return self;
}

static void symbol__delete(struct symbol *self, unsigned int priv_size)
{
	free(((void *)self) - priv_size);
}

static size_t symbol__fprintf(struct symbol *self, FILE *fp)
{
	return fprintf(fp, " %llx-%llx %s\n",
		       self->start, self->end, self->name);
}

struct dso *dso__new(const char *name, unsigned int sym_priv_size)
{
	struct dso *self = malloc(sizeof(*self) + strlen(name) + 1);

	if (self != NULL) {
		strcpy(self->name, name);
		self->syms = RB_ROOT;
		self->sym_priv_size = sym_priv_size;
		self->find_symbol = dso__find_symbol;
	}

	return self;
}

static void dso__delete_symbols(struct dso *self)
{
	struct symbol *pos;
	struct rb_node *next = rb_first(&self->syms);

	while (next) {
		pos = rb_entry(next, struct symbol, rb_node);
		next = rb_next(&pos->rb_node);
		rb_erase(&pos->rb_node, &self->syms);
		symbol__delete(pos, self->sym_priv_size);
	}
}

void dso__delete(struct dso *self)
{
	dso__delete_symbols(self);
	free(self);
}

static void dso__insert_symbol(struct dso *self, struct symbol *sym)
{
	struct rb_node **p = &self->syms.rb_node;
	struct rb_node *parent = NULL;
	const uint64_t ip = sym->start;
	struct symbol *s;

	while (*p != NULL) {
		parent = *p;
		s = rb_entry(parent, struct symbol, rb_node);
		if (ip < s->start)
			p = &(*p)->rb_left;
		else
			p = &(*p)->rb_right;
	}
	rb_link_node(&sym->rb_node, parent, p);
	rb_insert_color(&sym->rb_node, &self->syms);
}

struct symbol *dso__find_symbol(struct dso *self, uint64_t ip)
{
	struct rb_node *n;

	if (self == NULL)
		return NULL;

	n = self->syms.rb_node;

	while (n) {
		struct symbol *s = rb_entry(n, struct symbol, rb_node);

		if (ip < s->start)
			n = n->rb_left;
		else if (ip > s->end)
			n = n->rb_right;
		else
			return s;
	}

	return NULL;
}

size_t dso__fprintf(struct dso *self, FILE *fp)
{
	size_t ret = fprintf(fp, "dso: %s\n", self->name);

	struct rb_node *nd;
	for (nd = rb_first(&self->syms); nd; nd = rb_next(nd)) {
		struct symbol *pos = rb_entry(nd, struct symbol, rb_node);
		ret += symbol__fprintf(pos, fp);
	}

	return ret;
}

static int dso__load_kallsyms(struct dso *self, symbol_filter_t filter, int verbose)
{
	struct rb_node *nd, *prevnd;
	char *line = NULL;
	size_t n;
	FILE *file = fopen("/proc/kallsyms", "r");

	if (file == NULL)
		goto out_failure;

	while (!feof(file)) {
		__u64 start;
		struct symbol *sym;
		int line_len, len;
		char symbol_type;

		line_len = getline(&line, &n, file);
		if (line_len < 0)
			break;

		if (!line)
			goto out_failure;

		line[--line_len] = '\0'; /* \n */

		len = hex2u64(line, &start);

		len++;
		if (len + 2 >= line_len)
			continue;

		symbol_type = toupper(line[len]);
		/*
		 * We're interested only in code ('T'ext)
		 */
		if (symbol_type != 'T' && symbol_type != 'W')
			continue;
		/*
		 * Well fix up the end later, when we have all sorted.
		 */
		sym = symbol__new(start, 0xdead, line + len + 2,
				  self->sym_priv_size);

		if (sym == NULL)
			goto out_delete_line;

		if (filter && filter(self, sym))
			symbol__delete(sym, self->sym_priv_size);
		else
			dso__insert_symbol(self, sym);
	}

	/*
	 * Now that we have all sorted out, just set the ->end of all
	 * symbols
	 */
	prevnd = rb_first(&self->syms);

	if (prevnd == NULL)
		goto out_delete_line;

	for (nd = rb_next(prevnd); nd; nd = rb_next(nd)) {
		struct symbol *prev = rb_entry(prevnd, struct symbol, rb_node),
			      *curr = rb_entry(nd, struct symbol, rb_node);

		prev->end = curr->start - 1;
		prevnd = nd;
	}

	free(line);
	fclose(file);

	return 0;

out_delete_line:
	free(line);
out_failure:
	return -1;
}

/**
 * elf_symtab__for_each_symbol - iterate thru all the symbols
 *
 * @self: struct elf_symtab instance to iterate
 * @index: uint32_t index
 * @sym: GElf_Sym iterator
 */
#define elf_symtab__for_each_symbol(syms, nr_syms, index, sym) \
	for (index = 0, gelf_getsym(syms, index, &sym);\
	     index < nr_syms; \
	     index++, gelf_getsym(syms, index, &sym))

static inline uint8_t elf_sym__type(const GElf_Sym *sym)
{
	return GELF_ST_TYPE(sym->st_info);
}

static inline int elf_sym__is_function(const GElf_Sym *sym)
{
	return elf_sym__type(sym) == STT_FUNC &&
	       sym->st_name != 0 &&
	       sym->st_shndx != SHN_UNDEF &&
	       sym->st_size != 0;
}

static inline const char *elf_sym__name(const GElf_Sym *sym,
					const Elf_Data *symstrs)
{
	return symstrs->d_buf + sym->st_name;
}

static Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
				    GElf_Shdr *shp, const char *name,
				    size_t *index)
{
	Elf_Scn *sec = NULL;
	size_t cnt = 1;

	while ((sec = elf_nextscn(elf, sec)) != NULL) {
		char *str;

		gelf_getshdr(sec, shp);
		str = elf_strptr(elf, ep->e_shstrndx, shp->sh_name);
		if (!strcmp(name, str)) {
			if (index)
				*index = cnt;
			break;
		}
		++cnt;
	}

	return sec;
}

#define elf_section__for_each_rel(reldata, pos, pos_mem, idx, nr_entries) \
	for (idx = 0, pos = gelf_getrel(reldata, 0, &pos_mem); \
	     idx < nr_entries; \
	     ++idx, pos = gelf_getrel(reldata, idx, &pos_mem))

#define elf_section__for_each_rela(reldata, pos, pos_mem, idx, nr_entries) \
	for (idx = 0, pos = gelf_getrela(reldata, 0, &pos_mem); \
	     idx < nr_entries; \
	     ++idx, pos = gelf_getrela(reldata, idx, &pos_mem))

static int dso__synthesize_plt_symbols(struct  dso *self, Elf *elf,
				       GElf_Ehdr *ehdr, Elf_Scn *scn_dynsym,
				       GElf_Shdr *shdr_dynsym,
				       size_t dynsym_idx)
{
	uint32_t nr_rel_entries, idx;
	GElf_Sym sym;
	__u64 plt_offset;
	GElf_Shdr shdr_plt;
	struct symbol *f;
	GElf_Shdr shdr_rel_plt;
	Elf_Data *reldata, *syms, *symstrs;
	Elf_Scn *scn_plt_rel, *scn_symstrs;
	char sympltname[1024];
	int nr = 0, symidx;

	scn_plt_rel = elf_section_by_name(elf, ehdr, &shdr_rel_plt,
					  ".rela.plt", NULL);
	if (scn_plt_rel == NULL) {
		scn_plt_rel = elf_section_by_name(elf, ehdr, &shdr_rel_plt,
						  ".rel.plt", NULL);
		if (scn_plt_rel == NULL)
			return 0;
	}

	if (shdr_rel_plt.sh_link != dynsym_idx)
		return 0;

	if (elf_section_by_name(elf, ehdr, &shdr_plt, ".plt", NULL) == NULL)
		return 0;

	/*
	 * Fetch the relocation section to find the indexes to the GOT
	 * and the symbols in the .dynsym they refer to.
	 */
	reldata = elf_getdata(scn_plt_rel, NULL);
	if (reldata == NULL)
		return -1;

	syms = elf_getdata(scn_dynsym, NULL);
	if (syms == NULL)
		return -1;

	scn_symstrs = elf_getscn(elf, shdr_dynsym->sh_link);
	if (scn_symstrs == NULL)
		return -1;

	symstrs = elf_getdata(scn_symstrs, NULL);
	if (symstrs == NULL)
		return -1;

	nr_rel_entries = shdr_rel_plt.sh_size / shdr_rel_plt.sh_entsize;
	plt_offset = shdr_plt.sh_offset;

	if (shdr_rel_plt.sh_type == SHT_RELA) {
		GElf_Rela pos_mem, *pos;

		elf_section__for_each_rela(reldata, pos, pos_mem, idx,
					   nr_rel_entries) {
			symidx = GELF_R_SYM(pos->r_info);
			plt_offset += shdr_plt.sh_entsize;
			gelf_getsym(syms, symidx, &sym);
			snprintf(sympltname, sizeof(sympltname),
				 "%s@plt", elf_sym__name(&sym, symstrs));

			f = symbol__new(plt_offset, shdr_plt.sh_entsize,
					sympltname, self->sym_priv_size);
			if (!f)
				return -1;

			dso__insert_symbol(self, f);
			++nr;
		}
	} else if (shdr_rel_plt.sh_type == SHT_REL) {
		GElf_Rel pos_mem, *pos;
		elf_section__for_each_rel(reldata, pos, pos_mem, idx,
					  nr_rel_entries) {
			symidx = GELF_R_SYM(pos->r_info);
			plt_offset += shdr_plt.sh_entsize;
			gelf_getsym(syms, symidx, &sym);
			snprintf(sympltname, sizeof(sympltname),
				 "%s@plt", elf_sym__name(&sym, symstrs));

			f = symbol__new(plt_offset, shdr_plt.sh_entsize,
					sympltname, self->sym_priv_size);
			if (!f)
				return -1;

			dso__insert_symbol(self, f);
			++nr;
		}
	} else {
		/*
		 * TODO: There are still one more shdr_rel_plt.sh_type
		 * I have to investigate, but probably should be ignored.
		 */
	}

	return nr;
}

static int dso__load_sym(struct dso *self, int fd, const char *name,
			 symbol_filter_t filter, int verbose)
{
	Elf_Data *symstrs;
	uint32_t nr_syms;
	int err = -1;
	uint32_t index;
	GElf_Ehdr ehdr;
	GElf_Shdr shdr;
	Elf_Data *syms;
	GElf_Sym sym;
	Elf_Scn *sec, *sec_dynsym;
	Elf *elf;
	size_t dynsym_idx;
	int nr = 0;

	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
	if (elf == NULL) {
		if (verbose)
			fprintf(stderr, "%s: cannot read %s ELF file.\n",
				__func__, name);
		goto out_close;
	}

	if (gelf_getehdr(elf, &ehdr) == NULL) {
		if (verbose)
			fprintf(stderr, "%s: cannot get elf header.\n", __func__);
		goto out_elf_end;
	}

	/*
	 * We need to check if we have a .dynsym, so that we can handle the
	 * .plt, synthesizing its symbols, that aren't on the symtabs (be it
	 * .dynsym or .symtab)
	 */
	sec_dynsym = elf_section_by_name(elf, &ehdr, &shdr,
					 ".dynsym", &dynsym_idx);
	if (sec_dynsym != NULL) {
		nr = dso__synthesize_plt_symbols(self, elf, &ehdr,
						 sec_dynsym, &shdr,
						 dynsym_idx);
		if (nr < 0)
			goto out_elf_end;
	}

	/*
	 * But if we have a full .symtab (that is a superset of .dynsym) we
	 * should add the symbols not in the .dynsyn
	 */
	sec = elf_section_by_name(elf, &ehdr, &shdr, ".symtab", NULL);
	if (sec == NULL) {
		if (sec_dynsym == NULL)
			goto out_elf_end;

		sec = sec_dynsym;
		gelf_getshdr(sec, &shdr);
	}

	syms = elf_getdata(sec, NULL);
	if (syms == NULL)
		goto out_elf_end;

	sec = elf_getscn(elf, shdr.sh_link);
	if (sec == NULL)
		goto out_elf_end;

	symstrs = elf_getdata(sec, NULL);
	if (symstrs == NULL)
		goto out_elf_end;

	nr_syms = shdr.sh_size / shdr.sh_entsize;

	elf_symtab__for_each_symbol(syms, nr_syms, index, sym) {
		struct symbol *f;

		if (!elf_sym__is_function(&sym))
			continue;

		sec = elf_getscn(elf, sym.st_shndx);
		if (!sec)
			goto out_elf_end;

		gelf_getshdr(sec, &shdr);
		sym.st_value -= shdr.sh_addr - shdr.sh_offset;

		f = symbol__new(sym.st_value, sym.st_size,
				elf_sym__name(&sym, symstrs),
				self->sym_priv_size);
		if (!f)
			goto out_elf_end;

		if (filter && filter(self, f))
			symbol__delete(f, self->sym_priv_size);
		else {
			dso__insert_symbol(self, f);
			nr++;
		}
	}

	err = nr;
out_elf_end:
	elf_end(elf);
out_close:
	return err;
}

int dso__load(struct dso *self, symbol_filter_t filter, int verbose)
{
	int size = strlen(self->name) + sizeof("/usr/lib/debug%s.debug");
	char *name = malloc(size);
	int variant = 0;
	int ret = -1;
	int fd;

	if (!name)
		return -1;

more:
	do {
		switch (variant) {
		case 0: /* Fedora */
			snprintf(name, size, "/usr/lib/debug%s.debug", self->name);
			break;
		case 1: /* Ubuntu */
			snprintf(name, size, "/usr/lib/debug%s", self->name);
			break;
		case 2: /* Sane people */
			snprintf(name, size, "%s", self->name);
			break;

		default:
			goto out;
		}
		variant++;

		fd = open(name, O_RDONLY);
	} while (fd < 0);

	ret = dso__load_sym(self, fd, name, filter, verbose);
	close(fd);

	/*
	 * Some people seem to have debuginfo files _WITHOUT_ debug info!?!?
	 */
	if (!ret)
		goto more;

out:
	free(name);
	return ret;
}

static int dso__load_vmlinux(struct dso *self, const char *vmlinux,
			     symbol_filter_t filter, int verbose)
{
	int err, fd = open(vmlinux, O_RDONLY);

	if (fd < 0)
		return -1;

	err = dso__load_sym(self, fd, vmlinux, filter, verbose);
	close(fd);

	return err;
}

int dso__load_kernel(struct dso *self, const char *vmlinux,
		     symbol_filter_t filter, int verbose)
{
	int err = -1;

	if (vmlinux)
		err = dso__load_vmlinux(self, vmlinux, filter, verbose);

	if (err)
		err = dso__load_kallsyms(self, filter, verbose);

	return err;
}

void symbol__init(void)
{
	elf_version(EV_CURRENT);
}