Date:	Mon, 21 May 2012 13:47:39 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Namhyung Kim <namhyung.kim@....com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] perf symbols: Implement poor man's ELF parser

On Mon, May 14, 2012 at 04:10:24PM +0900, Namhyung Kim wrote:
> Implement minimalistic elf parser for getting build-id.
> A couple of structs needed are copied from elf.h and
> the parser only looks for PT_NOTE program header to
> check build-id.
> ---
>  tools/perf/util/elf-minimal.h    |  153 ++++++++++++++++++++++++
>  tools/perf/util/symbol-minimal.c |  244 ++++++++++++++++++++++++++++++++++++--
>  2 files changed, 388 insertions(+), 9 deletions(-)
>  create mode 100644 tools/perf/util/elf-minimal.h
> 
> diff --git a/tools/perf/util/elf-minimal.h b/tools/perf/util/elf-minimal.h
> new file mode 100644
> index 000000000000..26540b5718a1
> --- /dev/null
> +++ b/tools/perf/util/elf-minimal.h
> @@ -0,0 +1,153 @@
> +/*
> + * Minimal ELF definitions for parsing build-id.
> + */
> +/* This file defines standard ELF types, structures, and macros.
> +   Copyright (C) 1995-2003,2004,2005,2006,2007,2008,2009,2010,2011
> +	Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, write to the Free
> +   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
> +   02111-1307 USA.  */

I can see all this exported in:

[jolsa@...p-26-214 perf]$ rpm -qf /usr/include/elf.h
glibc-headers-2.14.90-24.fc16.6.x86_64

so maybe we dont need to add our own, since glic-headers
seems crutial anyway ;)

jirka

> +
> +#ifndef _ELF_MINIMAL_H
> +#define	_ELF_MINIMAL_H 1
> +
> +/* Standard ELF types.  */
> +
> +#include <stdint.h>
> +
> +/* Type for a 16-bit quantity.  */
> +typedef uint16_t Elf32_Half;
> +typedef uint16_t Elf64_Half;
> +
> +/* Types for signed and unsigned 32-bit quantities.  */
> +typedef uint32_t Elf32_Word;
> +typedef	int32_t  Elf32_Sword;
> +typedef uint32_t Elf64_Word;
> +typedef	int32_t  Elf64_Sword;
> +
> +/* Types for signed and unsigned 64-bit quantities.  */
> +typedef uint64_t Elf32_Xword;
> +typedef	int64_t  Elf32_Sxword;
> +typedef uint64_t Elf64_Xword;
> +typedef	int64_t  Elf64_Sxword;
> +
> +/* Type of addresses.  */
> +typedef uint32_t Elf32_Addr;
> +typedef uint64_t Elf64_Addr;
> +
> +/* Type of file offsets.  */
> +typedef uint32_t Elf32_Off;
> +typedef uint64_t Elf64_Off;
> +
> +
> +/* The ELF file header.  This appears at the start of every ELF file.  */
> +
> +#define EI_NIDENT (16)
> +
> +typedef struct
> +{
> +  unsigned char	e_ident[EI_NIDENT];	/* Magic number and other info */
> +  Elf32_Half	e_type;			/* Object file type */
> +  Elf32_Half	e_machine;		/* Architecture */
> +  Elf32_Word	e_version;		/* Object file version */
> +  Elf32_Addr	e_entry;		/* Entry point virtual address */
> +  Elf32_Off	e_phoff;		/* Program header table file offset */
> +  Elf32_Off	e_shoff;		/* Section header table file offset */
> +  Elf32_Word	e_flags;		/* Processor-specific flags */
> +  Elf32_Half	e_ehsize;		/* ELF header size in bytes */
> +  Elf32_Half	e_phentsize;		/* Program header table entry size */
> +  Elf32_Half	e_phnum;		/* Program header table entry count */
> +  Elf32_Half	e_shentsize;		/* Section header table entry size */
> +  Elf32_Half	e_shnum;		/* Section header table entry count */
> +  Elf32_Half	e_shstrndx;		/* Section header string table index */
> +} Elf32_Ehdr;
> +
> +typedef struct
> +{
> +  unsigned char	e_ident[EI_NIDENT];	/* Magic number and other info */
> +  Elf64_Half	e_type;			/* Object file type */
> +  Elf64_Half	e_machine;		/* Architecture */
> +  Elf64_Word	e_version;		/* Object file version */
> +  Elf64_Addr	e_entry;		/* Entry point virtual address */
> +  Elf64_Off	e_phoff;		/* Program header table file offset */
> +  Elf64_Off	e_shoff;		/* Section header table file offset */
> +  Elf64_Word	e_flags;		/* Processor-specific flags */
> +  Elf64_Half	e_ehsize;		/* ELF header size in bytes */
> +  Elf64_Half	e_phentsize;		/* Program header table entry size */
> +  Elf64_Half	e_phnum;		/* Program header table entry count */
> +  Elf64_Half	e_shentsize;		/* Section header table entry size */
> +  Elf64_Half	e_shnum;		/* Section header table entry count */
> +  Elf64_Half	e_shstrndx;		/* Section header string table index */
> +} Elf64_Ehdr;
> +
> +/* Conglomeration of the identification bytes, for easy testing as a word.  */
> +#define	ELFMAG		"\177ELF"
> +#define	SELFMAG		4
> +
> +#define EI_CLASS	4		/* File class byte index */
> +#define ELFCLASSNONE	0		/* Invalid class */
> +#define ELFCLASS32	1		/* 32-bit objects */
> +#define ELFCLASS64	2		/* 64-bit objects */
> +#define ELFCLASSNUM	3
> +
> +#define EI_DATA		5		/* Data encoding byte index */
> +#define ELFDATANONE	0		/* Invalid data encoding */
> +#define ELFDATA2LSB	1		/* 2's complement, little endian */
> +#define ELFDATA2MSB	2		/* 2's complement, big endian */
> +#define ELFDATANUM	3
> +
> +#define EI_VERSION	6		/* File version byte index */
> +					/* Value must be EV_CURRENT */
> +
> +/* Legal values for e_version (version).  */
> +
> +#define EV_NONE		0		/* Invalid ELF version */
> +#define EV_CURRENT	1		/* Current version */
> +#define EV_NUM		2
> +
> +#define EI_PAD		9		/* Byte index of padding bytes */
> +
> +/* Program segment header.  */
> +
> +typedef struct
> +{
> +  Elf32_Word	p_type;			/* Segment type */
> +  Elf32_Off	p_offset;		/* Segment file offset */
> +  Elf32_Addr	p_vaddr;		/* Segment virtual address */
> +  Elf32_Addr	p_paddr;		/* Segment physical address */
> +  Elf32_Word	p_filesz;		/* Segment size in file */
> +  Elf32_Word	p_memsz;		/* Segment size in memory */
> +  Elf32_Word	p_flags;		/* Segment flags */
> +  Elf32_Word	p_align;		/* Segment alignment */
> +} Elf32_Phdr;
> +
> +typedef struct
> +{
> +  Elf64_Word	p_type;			/* Segment type */
> +  Elf64_Word	p_flags;		/* Segment flags */
> +  Elf64_Off	p_offset;		/* Segment file offset */
> +  Elf64_Addr	p_vaddr;		/* Segment virtual address */
> +  Elf64_Addr	p_paddr;		/* Segment physical address */
> +  Elf64_Xword	p_filesz;		/* Segment size in file */
> +  Elf64_Xword	p_memsz;		/* Segment size in memory */
> +  Elf64_Xword	p_align;		/* Segment alignment */
> +} Elf64_Phdr;
> +
> +/* Legal values for p_type (segment type).  */
> +
> +#define PT_NOTE		4		/* Auxiliary information */
> +
> +#endif	/* _ELF_MINIMAL_H */
> diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
> index 2917ede1d5ba..dfef571abc9b 100644
> --- a/tools/perf/util/symbol-minimal.c
> +++ b/tools/perf/util/symbol-minimal.c
> @@ -1,29 +1,255 @@
>  #include "symbol.h"
> +#include "elf-minimal.h"
>  
> +#include <stdio.h>
> +#include <fcntl.h>
> +#include <string.h>
> +#include <byteswap.h>
> +#include <sys/stat.h>
>  
> -int filename__read_build_id(const char *filename __used, void *bf __used,
> -			    size_t size __used)
> +static bool check_need_swap(int file_endian)
>  {
> -	return -1;
> +	const int data = 1;
> +	u8 *check = (u8 *)&data;
> +	int host_endian;
> +
> +	if (check[0] == 1)
> +		host_endian = ELFDATA2LSB;
> +	else
> +		host_endian = ELFDATA2MSB;
> +
> +	return host_endian != file_endian;
>  }
>  
> -int sysfs__read_build_id(const char *filename __used, void *build_id __used,
> -			 size_t size __used)
> +#define NOTE_ALIGN(sz) (((sz) + 3) & ~3)
> +
> +#define NT_GNU_BUILD_ID	3
> +
> +static int read_build_id(void *note_data, size_t note_len, void *bf,
> +			 size_t size, bool need_swap)
>  {
> +	struct {
> +		u32 n_namesz;
> +		u32 n_descsz;
> +		u32 n_type;
> +	} *nhdr;
> +	void *ptr;
> +
> +	ptr = note_data;
> +	while (ptr < (note_data + note_len)) {
> +		const char *name;
> +		size_t namesz, descsz;
> +
> +		nhdr = ptr;
> +		if (need_swap) {
> +			nhdr->n_namesz = bswap_32(nhdr->n_namesz);
> +			nhdr->n_descsz = bswap_32(nhdr->n_descsz);
> +			nhdr->n_type = bswap_32(nhdr->n_type);
> +		}
> +
> +		namesz = NOTE_ALIGN(nhdr->n_namesz);
> +		descsz = NOTE_ALIGN(nhdr->n_descsz);
> +
> +		ptr += sizeof(*nhdr);
> +		name = ptr;
> +		ptr += namesz;
> +		if (nhdr->n_type == NT_GNU_BUILD_ID &&
> +		    nhdr->n_namesz == sizeof("GNU")) {
> +			if (memcmp(name, "GNU", sizeof("GNU")) == 0) {
> +				size_t sz = min(size, descsz);
> +				memcpy(bf, ptr, sz);
> +				memset(bf + sz, 0, size - sz);
> +				return 0;
> +			}
> +		}
> +		ptr += descsz;
> +	}
> +
>  	return -1;
>  }
>  
> +/*
> + * Just try PT_NOTE header otherwise fails
> + */
> +int filename__read_build_id(const char *filename, void *bf, size_t size)
> +{
> +	FILE *fp;
> +	int ret = -1;
> +	bool need_swap = false;
> +	u8 e_ident[EI_NIDENT];
> +	size_t buf_size;
> +	void *buf;
> +	int i;
> +
> +	fp = fopen(filename, "r");
> +	if (fp == NULL)
> +		return -1;
> +
> +	if (fread(e_ident, sizeof(e_ident), 1, fp) != 1)
> +		goto out;
> +
> +	if (memcmp(e_ident, ELFMAG, SELFMAG) ||
> +	    e_ident[EI_VERSION] != EV_CURRENT)
> +		goto out;
> +
> +	need_swap = check_need_swap(e_ident[EI_DATA]);
> +
> +	/* for simplicity */
> +	fseek(fp, 0, SEEK_SET);
> +
> +	if (e_ident[EI_CLASS] == ELFCLASS32) {
> +		Elf32_Ehdr ehdr;
> +		Elf32_Phdr *phdr;
> +
> +		if (fread(&ehdr, sizeof(ehdr), 1, fp) != 1)
> +			goto out;
> +
> +		if (need_swap) {
> +			ehdr.e_phoff = bswap_32(ehdr.e_phoff);
> +			ehdr.e_phentsize = bswap_16(ehdr.e_phentsize);
> +			ehdr.e_phnum = bswap_16(ehdr.e_phnum);
> +		}
> +
> +		buf_size = ehdr.e_phentsize * ehdr.e_phnum;
> +		buf = malloc(buf_size);
> +		if (buf == NULL)
> +			goto out;
> +
> +		fseek(fp, ehdr.e_phoff, SEEK_SET);
> +		if (fread(buf, buf_size, 1, fp) != 1)
> +			goto out_free;
> +
> +		for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
> +			void *tmp;
> +
> +			if (need_swap) {
> +				phdr->p_type = bswap_32(phdr->p_type);
> +				phdr->p_offset = bswap_32(phdr->p_offset);
> +				phdr->p_filesz = bswap_32(phdr->p_filesz);
> +			}
> +
> +			if (phdr->p_type != PT_NOTE)
> +				continue;
> +
> +			buf_size = phdr->p_filesz;
> +			tmp = realloc(buf, buf_size);
> +			if (tmp == NULL)
> +				goto out_free;
> +
> +			buf = tmp;
> +			fseek(fp, phdr->p_offset, SEEK_SET);
> +			if (fread(buf, buf_size, 1, fp) != 1)
> +				goto out_free;
> +
> +			ret = read_build_id(buf, buf_size, bf, size, need_swap);
> +			if (ret == 0)
> +				ret = size;
> +			break;
> +		}
> +	} else {
> +		Elf64_Ehdr ehdr;
> +		Elf64_Phdr *phdr;
> +
> +		if (fread(&ehdr, sizeof(ehdr), 1, fp) != 1)
> +			goto out;
> +
> +		if (need_swap) {
> +			ehdr.e_phoff = bswap_64(ehdr.e_phoff);
> +			ehdr.e_phentsize = bswap_16(ehdr.e_phentsize);
> +			ehdr.e_phnum = bswap_16(ehdr.e_phnum);
> +		}
> +
> +		buf_size = ehdr.e_phentsize * ehdr.e_phnum;
> +		buf = malloc(buf_size);
> +		if (buf == NULL)
> +			goto out;
> +
> +		fseek(fp, ehdr.e_phoff, SEEK_SET);
> +		if (fread(buf, buf_size, 1, fp) != 1)
> +			goto out_free;
> +
> +		for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
> +			void *tmp;
> +
> +			if (need_swap) {
> +				phdr->p_type = bswap_32(phdr->p_type);
> +				phdr->p_offset = bswap_64(phdr->p_offset);
> +				phdr->p_filesz = bswap_64(phdr->p_filesz);
> +			}
> +
> +			if (phdr->p_type != PT_NOTE)
> +				continue;
> +
> +			buf_size = phdr->p_filesz;
> +			tmp = realloc(buf, buf_size);
> +			if (tmp == NULL)
> +				goto out_free;
> +
> +			buf = tmp;
> +			fseek(fp, phdr->p_offset, SEEK_SET);
> +			if (fread(buf, buf_size, 1, fp) != 1)
> +				goto out_free;
> +
> +			ret = read_build_id(buf, buf_size, bf, size, need_swap);
> +			if (ret == 0)
> +				ret = size;
> +			break;
> +		}
> +	}
> +out_free:
> +	free(buf);
> +out:
> +	fclose(fp);
> +	return ret;
> +}
> +
> +int sysfs__read_build_id(const char *filename, void *build_id, size_t size)
> +{
> +	int fd;
> +	int ret = -1;
> +	struct stat stbuf;
> +	size_t buf_size;
> +	void *buf;
> +
> +	fd = open(filename, O_RDONLY);
> +	if (fd < 0)
> +		return -1;
> +
> +	if (fstat(fd, &stbuf) < 0)
> +		goto out;
> +
> +	buf_size = stbuf.st_size;
> +	buf = malloc(buf_size);
> +	if (buf == NULL)
> +		goto out;
> +
> +	if (read(fd, buf, buf_size) != (ssize_t) buf_size)
> +		goto out_free;
> +
> +	ret = read_build_id(buf, buf_size, build_id, size, false);
> +out_free:
> +	free(buf);
> +out:
> +	close(fd);
> +	return ret;
> +}
> +
>  int dso__synthesize_plt_symbols(struct dso *dso __used, struct map *map __used,
>  				symbol_filter_t filter __used)
>  {
>  	return 0;
>  }
>  
> -int dso__load_sym(struct dso *dso __used, struct map *map __used,
> -		  const char *name __used, int fd __used,
> -		  symbol_filter_t filter __used, int kmodule __used,
> -		  int want_symtab __used)
> +int dso__load_sym(struct dso *dso, struct map *map __used, const char *name,
> +		  int fd __used, symbol_filter_t filter __used,
> +		  int kmodule __used, int want_symtab __used)
>  {
> +	unsigned char *build_id[BUILD_ID_SIZE];
> +
> +	if (filename__read_build_id(name, build_id, BUILD_ID_SIZE) > 0) {
> +		dso__set_build_id(dso, build_id);
> +		return 1;
> +	}
>  	return 0;
>  }
>  
> -- 
> 1.7.10.1
> 
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