[PATCH 11/16] perf symbol: introduce symsrc structure.

[Cody P Schafer <cody@linux.vnet.ibm.com>]

Factors opening of certain sections & tracking certain elf info into an
external structure.

The goal here is to keep multiple elfs (and their looked up
sections/indexes) around during the symbol generation process (in
dso__load()).

We need this to properly resolve symbols on PPC due to the
use of function descriptors & the .opd section (ie: symbols which are
functions don't point to their actual location, they point to their
function descriptor in .opd which contains their actual location.

It would be possible to just keep the (Elf *) around, but then we'd end
up with duplicate code for looking up the same sections and checking for
the existence of an important section wouldn't be as clean.

Additionally, move dso__swap_init() so we can use it.

Utilized by the later patch
"perf symbol: use both runtime and debug images"

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
---
 tools/perf/util/symbol.c | 240 +++++++++++++++++++++++++++++++----------------
 1 file changed, 161 insertions(+), 79 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 662d1a2..00a8226 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -993,6 +993,144 @@ static Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
 	return sec;
 }
 
+static int dso__swap_init(struct dso *dso, unsigned char eidata)
+{
+	static unsigned int const endian = 1;
+
+	dso->needs_swap = DSO_SWAP__NO;
+
+	switch (eidata) {
+	case ELFDATA2LSB:
+		/* We are big endian, DSO is little endian. */
+		if (*(unsigned char const *)&endian != 1)
+			dso->needs_swap = DSO_SWAP__YES;
+		break;
+
+	case ELFDATA2MSB:
+		/* We are little endian, DSO is big endian. */
+		if (*(unsigned char const *)&endian != 0)
+			dso->needs_swap = DSO_SWAP__YES;
+		break;
+
+	default:
+		pr_err("unrecognized DSO data encoding %d\n", eidata);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+struct symsrc {
+	Elf *elf;
+	GElf_Ehdr ehdr;
+
+	Elf_Scn *opdsec;
+	size_t opdidx;
+	GElf_Shdr opdshdr;
+
+	Elf_Scn *symtab;
+	GElf_Shdr symshdr;
+
+	Elf_Scn *dynsym;
+	size_t dynsym_idx;
+	GElf_Shdr dynshdr;
+
+	char *name;
+	int fd;
+	enum dso_binary_type type;
+
+	bool adjust_symbols;
+};
+
+static void symsrc__destroy(struct symsrc *ss)
+{
+	free(ss->name);
+	elf_end(ss->elf);
+	close(ss->fd);
+}
+
+static int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
+	enum dso_binary_type type)
+{
+	int err = -1;
+	GElf_Ehdr ehdr;
+	Elf *elf;
+	int fd;
+
+	fd = open(name, O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
+	if (elf == NULL) {
+		pr_debug("%s: cannot read %s ELF file.\n", __func__, name);
+		goto out_close;
+	}
+
+	if (gelf_getehdr(elf, &ehdr) == NULL) {
+		pr_debug("%s: cannot get elf header.\n", __func__);
+		goto out_elf_end;
+	}
+
+	if (dso__swap_init(dso, ehdr.e_ident[EI_DATA]))
+		goto out_elf_end;
+
+	/* Always reject images with a mismatched build-id: */
+	if (dso->has_build_id) {
+		u8 build_id[BUILD_ID_SIZE];
+
+		if (elf_read_build_id(elf, build_id, BUILD_ID_SIZE) < 0)
+			goto out_elf_end;
+
+		if (!dso__build_id_equal(dso, build_id))
+			goto out_elf_end;
+	}
+
+	ss->symtab = elf_section_by_name(elf, &ehdr, &ss->symshdr, ".symtab",
+			NULL);
+	if (ss->symshdr.sh_type != SHT_SYMTAB)
+		ss->symtab = NULL;
+
+	ss->dynsym_idx = 0;
+	ss->dynsym = elf_section_by_name(elf, &ehdr, &ss->dynshdr, ".dynsym",
+			&ss->dynsym_idx);
+	if (ss->dynshdr.sh_type != SHT_DYNSYM)
+		ss->dynsym = NULL;
+
+	ss->opdidx = 0;
+	ss->opdsec = elf_section_by_name(elf, &ehdr, &ss->opdshdr, ".opd",
+			&ss->opdidx);
+	if (ss->opdshdr.sh_type != SHT_PROGBITS)
+		ss->opdsec = NULL;
+
+	if (dso->kernel == DSO_TYPE_USER) {
+		GElf_Shdr shdr;
+		ss->adjust_symbols = (ehdr.e_type == ET_EXEC ||
+				elf_section_by_name(elf, &ehdr, &shdr,
+						     ".gnu.prelink_undo",
+						     NULL) != NULL);
+	} else {
+		ss->adjust_symbols = 0;
+	}
+
+	ss->name   = strdup(name);
+	if (!ss->name)
+		goto out_elf_end;
+
+	ss->elf    = elf;
+	ss->fd     = fd;
+	ss->ehdr   = ehdr;
+	ss->type   = type;
+
+	return 0;
+
+out_elf_end:
+	elf_end(elf);
+out_close:
+	close(fd);
+	return err;
+}
+
 #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; \
@@ -1192,35 +1330,8 @@ static size_t elf_addr_to_index(Elf *elf, GElf_Addr addr)
 	return -1;
 }
 
-static int dso__swap_init(struct dso *dso, unsigned char eidata)
-{
-	static unsigned int const endian = 1;
-
-	dso->needs_swap = DSO_SWAP__NO;
-
-	switch (eidata) {
-	case ELFDATA2LSB:
-		/* We are big endian, DSO is little endian. */
-		if (*(unsigned char const *)&endian != 1)
-			dso->needs_swap = DSO_SWAP__YES;
-		break;
-
-	case ELFDATA2MSB:
-		/* We are little endian, DSO is big endian. */
-		if (*(unsigned char const *)&endian != 0)
-			dso->needs_swap = DSO_SWAP__YES;
-		break;
-
-	default:
-		pr_err("unrecognized DSO data encoding %d\n", eidata);
-		return -EINVAL;
-	}
-
-	return 0;
-}
-
-static int dso__load_sym(struct dso *dso, struct map *map, const char *name,
-			 int fd, symbol_filter_t filter, int kmodule,
+static int dso__load_sym(struct dso *dso, struct map *map, struct symsrc *ss,
+		         symbol_filter_t filter, int kmodule,
 			 int want_symtab)
 {
 	struct kmap *kmap = dso->kernel ? map__kmap(map) : NULL;
@@ -1239,44 +1350,24 @@ static int dso__load_sym(struct dso *dso, struct map *map, const char *name,
 	int nr = 0;
 	size_t opdidx = 0;
 
-	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
-	if (elf == NULL) {
-		pr_debug("%s: cannot read %s ELF file.\n", __func__, name);
-		goto out_close;
-	}
+	elf = ss->elf;
+	ehdr = ss->ehdr;
+	sec = ss->symtab;
+	shdr = ss->symshdr;
 
-	if (gelf_getehdr(elf, &ehdr) == NULL) {
-		pr_debug("%s: cannot get elf header.\n", __func__);
-		goto out_elf_end;
-	}
-
-	if (dso__swap_init(dso, ehdr.e_ident[EI_DATA]))
-		goto out_elf_end;
-
-	/* Always reject images with a mismatched build-id: */
-	if (dso->has_build_id) {
-		u8 build_id[BUILD_ID_SIZE];
-
-		if (elf_read_build_id(elf, build_id, BUILD_ID_SIZE) < 0)
-			goto out_elf_end;
-
-		if (!dso__build_id_equal(dso, build_id))
-			goto out_elf_end;
-	}
-
-	sec = elf_section_by_name(elf, &ehdr, &shdr, ".symtab", NULL);
 	if (sec == NULL) {
 		if (want_symtab)
 			goto out_elf_end;
 
-		sec = elf_section_by_name(elf, &ehdr, &shdr, ".dynsym", NULL);
+		sec  = ss->dynsym;
+		shdr = ss->dynshdr;
 		if (sec == NULL)
 			goto out_elf_end;
 	}
 
-	opdsec = elf_section_by_name(elf, &ehdr, &opdshdr, ".opd", &opdidx);
-	if (opdshdr.sh_type != SHT_PROGBITS)
-		opdsec = NULL;
+	opdsec = ss->opdsec;
+	opdshdr = ss->opdshdr;
+	opdidx  = ss->opdidx;
 	if (opdsec)
 		opddata = elf_rawdata(opdsec, NULL);
 
@@ -1303,14 +1394,7 @@ static int dso__load_sym(struct dso *dso, struct map *map, const char *name,
 	nr_syms = shdr.sh_size / shdr.sh_entsize;
 
 	memset(&sym, 0, sizeof(sym));
-	if (dso->kernel == DSO_TYPE_USER) {
-		dso->adjust_symbols = (ehdr.e_type == ET_EXEC ||
-				elf_section_by_name(elf, &ehdr, &shdr,
-						     ".gnu.prelink_undo",
-						     NULL) != NULL);
-	} else {
-		dso->adjust_symbols = 0;
-	}
+	dso->adjust_symbols = ss->adjust_symbols;
 	elf_symtab__for_each_symbol(syms, nr_syms, idx, sym) {
 		struct symbol *f;
 		const char *elf_name = elf_sym__name(&sym, symstrs);
@@ -1466,8 +1550,6 @@ new_symbol:
 	}
 	err = nr;
 out_elf_end:
-	elf_end(elf);
-out_close:
 	return err;
 }
 
@@ -1811,7 +1893,7 @@ int dso__load(struct dso *dso, struct map *map, symbol_filter_t filter)
 {
 	char *name;
 	int ret = -1;
-	int fd;
+	struct symsrc ss;
 	u_int i;
 	struct machine *machine;
 	char *root_dir = (char *) "";
@@ -1871,13 +1953,12 @@ restart:
 			continue;
 
 		/* Name is now the name of the next image to try */
-		fd = open(name, O_RDONLY);
-		if (fd < 0)
+		if (symsrc__init(&ss, dso, name, dso->symtab_type) < 0)
 			continue;
 
-		ret = dso__load_sym(dso, map, name, fd, filter, 0,
+		ret = dso__load_sym(dso, map, &ss, filter, 0,
 				    want_symtab);
-		close(fd);
+		symsrc__destroy(&ss);
 
 		/*
 		 * Some people seem to have debuginfo files _WITHOUT_ debug
@@ -2163,22 +2244,23 @@ out_failure:
 int dso__load_vmlinux(struct dso *dso, struct map *map,
 		      const char *vmlinux, symbol_filter_t filter)
 {
-	int err = -1, fd;
+	int err = -1;
+	struct symsrc ss;
 	char symfs_vmlinux[PATH_MAX];
 
 	snprintf(symfs_vmlinux, sizeof(symfs_vmlinux), "%s%s",
 		 symbol_conf.symfs, vmlinux);
-	fd = open(symfs_vmlinux, O_RDONLY);
-	if (fd < 0)
-		return -1;
 
 	if (dso->kernel == DSO_TYPE_GUEST_KERNEL)
 		dso->symtab_type = DSO_BINARY_TYPE__GUEST_VMLINUX;
 	else
 		dso->symtab_type = DSO_BINARY_TYPE__VMLINUX;
 
-	err = dso__load_sym(dso, map, symfs_vmlinux, fd, filter, 0, 0);
-	close(fd);
+	if (symsrc__init(&ss, dso, symfs_vmlinux, dso->symtab_type))
+		return -1;
+
+	err = dso__load_sym(dso, map, &ss, filter, 0, 0);
+	symsrc__destroy(&ss);
 
 	if (err > 0) {
 		dso__set_long_name(dso, (char *)vmlinux);
-- 
1.7.11.3