[PATCH] perf lookup of ppc64 symbols

[PATCH] perf lookup of ppc64 symbols

[Eric B Munson]

Currently symbol resolution does not work for 64-bit programs
using perf.  For this to work perf needs to lookup symbol names in
the OPD.  This patch adds this functionality.  The OPD data is
used to find symbol names when available.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Eric B Munson <ebmunson@us.ibm.com>
---
 tools/perf/util/symbol.c |   37 ++++++++++++++++++++++++++++++++++---
 1 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index b63e571..971d0a0 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -933,6 +933,25 @@ static bool elf_sec__is_a(GElf_Shdr *self, Elf_Data *secstrs, enum map_type type
 	}
 }
 
+static size_t elf_addr_to_index(Elf *elf, GElf_Addr addr)
+{
+	Elf_Scn *sec = NULL;
+	GElf_Shdr shdr;
+	size_t cnt = 1;
+
+	while ((sec = elf_nextscn(elf, sec)) != NULL) {
+		gelf_getshdr(sec, &shdr);
+
+		if ((addr >= shdr.sh_addr) &&
+		    (addr < (shdr.sh_addr + shdr.sh_size)))
+			return cnt;
+
+		++cnt;
+	}
+
+	return -1;
+}
+
 static int dso__load_sym(struct dso *self, struct map *map, const char *name,
 			 int fd, symbol_filter_t filter, int kmodule)
 {
@@ -944,12 +963,13 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
 	int err = -1;
 	uint32_t idx;
 	GElf_Ehdr ehdr;
-	GElf_Shdr shdr;
-	Elf_Data *syms;
+	GElf_Shdr shdr, opdshdr;
+	Elf_Data *syms, *opddata = NULL;
 	GElf_Sym sym;
-	Elf_Scn *sec, *sec_strndx;
+	Elf_Scn *sec, *sec_strndx, *opdsec;
 	Elf *elf;
 	int nr = 0;
+	size_t opdidx = 0;
 
 	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
 	if (elf == NULL) {
@@ -969,6 +989,10 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
 			goto out_elf_end;
 	}
 
+	opdsec = elf_section_by_name(elf, &ehdr, &opdshdr, ".opd", &opdidx);
+	if (opdsec)
+		opddata = elf_rawdata(opdsec, NULL);
+
 	syms = elf_getdata(sec, NULL);
 	if (syms == NULL)
 		goto out_elf_end;
@@ -1013,6 +1037,13 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
 		if (!is_label && !elf_sym__is_a(&sym, map->type))
 			continue;
 
+		if (opdsec && sym.st_shndx == opdidx) {
+			u32 offset = sym.st_value - opdshdr.sh_addr;
+			u64 *opd = opddata->d_buf + offset;
+			sym.st_value = *opd;
+			sym.st_shndx = elf_addr_to_index(elf, sym.st_value);
+		}
+
 		sec = elf_getscn(elf, sym.st_shndx);
 		if (!sec)
 			goto out_elf_end;
-- 
1.7.0.4

Re: [PATCH] perf lookup of ppc64 symbols

[Anton Blanchard]

Hi,

> Currently symbol resolution does not work for 64-bit programs
> using perf.  For this to work perf needs to lookup symbol names in
> the OPD.  This patch adds this functionality.  The OPD data is
> used to find symbol names when available.

To clarify, this is an issue with 64bit architectures that use function
descriptors (eg ppc64). The problem is that a symbol doesn't point to a text
address, it points to a data area that contains (amongst other things) a
pointer to the text address.

We look for a section called ".opd" which is the function descriptor
area. To create the full symbol table, when we see a symbol in the function
descriptor section we load the first pointer and use that as the text
address. The only tricky part here is working out which section the
text address is in. Right now we have a loop which is sub optimal:

> +	while ((sec = elf_nextscn(elf, sec)) != NULL) {
> +		gelf_getshdr(sec, &shdr);
> +
> +		if ((addr >= shdr.sh_addr) &&
> +		    (addr < (shdr.sh_addr + shdr.sh_size)))
> +			return cnt;
> +
> +		++cnt;
> +	}

Anton

> Signed-off-by: Anton Blanchard <anton@samba.org>
> Signed-off-by: Eric B Munson <ebmunson@us.ibm.com>
> ---
>  tools/perf/util/symbol.c |   37 ++++++++++++++++++++++++++++++++++---
>  1 files changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index b63e571..971d0a0 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -933,6 +933,25 @@ static bool elf_sec__is_a(GElf_Shdr *self, Elf_Data *secstrs, enum map_type type
>  	}
>  }
>  
> +static size_t elf_addr_to_index(Elf *elf, GElf_Addr addr)
> +{
> +	Elf_Scn *sec = NULL;
> +	GElf_Shdr shdr;
> +	size_t cnt = 1;
> +
> +	while ((sec = elf_nextscn(elf, sec)) != NULL) {
> +		gelf_getshdr(sec, &shdr);
> +
> +		if ((addr >= shdr.sh_addr) &&
> +		    (addr < (shdr.sh_addr + shdr.sh_size)))
> +			return cnt;
> +
> +		++cnt;
> +	}
> +
> +	return -1;
> +}
> +
>  static int dso__load_sym(struct dso *self, struct map *map, const char *name,
>  			 int fd, symbol_filter_t filter, int kmodule)
>  {
> @@ -944,12 +963,13 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
>  	int err = -1;
>  	uint32_t idx;
>  	GElf_Ehdr ehdr;
> -	GElf_Shdr shdr;
> -	Elf_Data *syms;
> +	GElf_Shdr shdr, opdshdr;
> +	Elf_Data *syms, *opddata = NULL;
>  	GElf_Sym sym;
> -	Elf_Scn *sec, *sec_strndx;
> +	Elf_Scn *sec, *sec_strndx, *opdsec;
>  	Elf *elf;
>  	int nr = 0;
> +	size_t opdidx = 0;
>  
>  	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
>  	if (elf == NULL) {
> @@ -969,6 +989,10 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
>  			goto out_elf_end;
>  	}
>  
> +	opdsec = elf_section_by_name(elf, &ehdr, &opdshdr, ".opd", &opdidx);
> +	if (opdsec)
> +		opddata = elf_rawdata(opdsec, NULL);
> +
>  	syms = elf_getdata(sec, NULL);
>  	if (syms == NULL)
>  		goto out_elf_end;
> @@ -1013,6 +1037,13 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
>  		if (!is_label && !elf_sym__is_a(&sym, map->type))
>  			continue;
>  
> +		if (opdsec && sym.st_shndx == opdidx) {
> +			u32 offset = sym.st_value - opdshdr.sh_addr;
> +			u64 *opd = opddata->d_buf + offset;
> +			sym.st_value = *opd;
> +			sym.st_shndx = elf_addr_to_index(elf, sym.st_value);
> +		}
> +
>  		sec = elf_getscn(elf, sym.st_shndx);
>  		if (!sec)
>  			goto out_elf_end;
> -- 
> 1.7.0.4

Re: [PATCH] perf lookup of ppc64 symbols

[Arnaldo Carvalho de Melo]

Em Fri, Jun 18, 2010 at 12:46:08AM +1000, Anton Blanchard escreveu:
> 
> Hi,
> 
> > Currently symbol resolution does not work for 64-bit programs
> > using perf.  For this to work perf needs to lookup symbol names in
> > the OPD.  This patch adds this functionality.  The OPD data is
> > used to find symbol names when available.
> 
> To clarify, this is an issue with 64bit architectures that use function
> descriptors (eg ppc64). The problem is that a symbol doesn't point to a text
> address, it points to a data area that contains (amongst other things) a
> pointer to the text address.
> 
> We look for a section called ".opd" which is the function descriptor
> area. To create the full symbol table, when we see a symbol in the function
> descriptor section we load the first pointer and use that as the text
> address. The only tricky part here is working out which section the
> text address is in. Right now we have a loop which is sub optimal:

I'll update the comment in Eric's patch and apply this to perf/core, for
.36, we can optimize this later, correctness first :-)

- Arnaldo

Re: [PATCH] perf lookup of ppc64 symbols

[Arnaldo Carvalho de Melo]

Em Thu, Jun 17, 2010 at 12:17:05PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Fri, Jun 18, 2010 at 12:46:08AM +1000, Anton Blanchard escreveu:
> > address. The only tricky part here is working out which section the
> > text address is in. Right now we have a loop which is sub optimal:
> 
> I'll update the comment in Eric's patch and apply this to perf/core, for
> .36, we can optimize this later, correctness first :-)

Also we only call dso__load lazily, when we find a hit in that DSO that
we want to resolve to a symbol, so it should be ok as-is.

- Arnaldo

[tip:perf/core] perf symbols: Function descriptor symbol lookup

[tip-bot for Eric B Munson]

Commit-ID:  70c3856b2f1304e0abc65f1b96a8c60ddfc0fb9e
Gitweb:     http://git.kernel.org/tip/70c3856b2f1304e0abc65f1b96a8c60ddfc0fb9e
Author:     Eric B Munson <ebmunson@us.ibm.com>
AuthorDate: Mon, 14 Jun 2010 14:56:33 +0100
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Thu, 17 Jun 2010 10:06:27 -0300

perf symbols: Function descriptor symbol lookup

Currently symbol resolution does not work for 64-bit programs on architectures
that use function descriptors such as ppc64.

The problem is that a symbol doesn't point to a text address, it points to a
data area that contains (amongst other things) a pointer to the text address.

We look for a section called ".opd" which is the function descriptor area. To
create the full symbol table, when we see a symbol in the function descriptor
section we load the first pointer and use that as the text address.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <1276523793-15422-1-git-send-email-ebmunson@us.ibm.com>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Eric B Munson <ebmunson@us.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/symbol.c |   37 ++++++++++++++++++++++++++++++++++---
 1 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index b63e571..971d0a0 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -933,6 +933,25 @@ static bool elf_sec__is_a(GElf_Shdr *self, Elf_Data *secstrs, enum map_type type
 	}
 }
 
+static size_t elf_addr_to_index(Elf *elf, GElf_Addr addr)
+{
+	Elf_Scn *sec = NULL;
+	GElf_Shdr shdr;
+	size_t cnt = 1;
+
+	while ((sec = elf_nextscn(elf, sec)) != NULL) {
+		gelf_getshdr(sec, &shdr);
+
+		if ((addr >= shdr.sh_addr) &&
+		    (addr < (shdr.sh_addr + shdr.sh_size)))
+			return cnt;
+
+		++cnt;
+	}
+
+	return -1;
+}
+
 static int dso__load_sym(struct dso *self, struct map *map, const char *name,
 			 int fd, symbol_filter_t filter, int kmodule)
 {
@@ -944,12 +963,13 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
 	int err = -1;
 	uint32_t idx;
 	GElf_Ehdr ehdr;
-	GElf_Shdr shdr;
-	Elf_Data *syms;
+	GElf_Shdr shdr, opdshdr;
+	Elf_Data *syms, *opddata = NULL;
 	GElf_Sym sym;
-	Elf_Scn *sec, *sec_strndx;
+	Elf_Scn *sec, *sec_strndx, *opdsec;
 	Elf *elf;
 	int nr = 0;
+	size_t opdidx = 0;
 
 	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
 	if (elf == NULL) {
@@ -969,6 +989,10 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
 			goto out_elf_end;
 	}
 
+	opdsec = elf_section_by_name(elf, &ehdr, &opdshdr, ".opd", &opdidx);
+	if (opdsec)
+		opddata = elf_rawdata(opdsec, NULL);
+
 	syms = elf_getdata(sec, NULL);
 	if (syms == NULL)
 		goto out_elf_end;
@@ -1013,6 +1037,13 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
 		if (!is_label && !elf_sym__is_a(&sym, map->type))
 			continue;
 
+		if (opdsec && sym.st_shndx == opdidx) {
+			u32 offset = sym.st_value - opdshdr.sh_addr;
+			u64 *opd = opddata->d_buf + offset;
+			sym.st_value = *opd;
+			sym.st_shndx = elf_addr_to_index(elf, sym.st_value);
+		}
+
 		sec = elf_getscn(elf, sym.st_shndx);
 		if (!sec)
 			goto out_elf_end;