linux-kernel - Re: [PATCH v0 07/71] perf tools: Record whether a dso is 64-bit

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Date:	Sun, 15 Dec 2013 20:16:22 -0700
From:	David Ahern <dsahern@...il.com>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH v0 07/71] perf tools: Record whether a dso is 64-bit

On 12/11/13, 5:36 AM, Alexander Shishkin wrote:
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index a0c7c59..80817ec 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -446,6 +446,7 @@ struct dso *dso__new(const char *name)
>   		dso->cache = RB_ROOT;
>   		dso->symtab_type = DSO_BINARY_TYPE__NOT_FOUND;
>   		dso->data_type   = DSO_BINARY_TYPE__NOT_FOUND;
> +		dso->is_64_bit = (sizeof(void *) == 8);
>   		dso->loaded = 0;
>   		dso->rel = 0;
>   		dso->sorted_by_name = 0;
> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> index 384f2d9..62680e1 100644
> --- a/tools/perf/util/dso.h
> +++ b/tools/perf/util/dso.h
> @@ -91,6 +91,7 @@ struct dso {
>   	u8		 annotate_warned:1;
>   	u8		 sname_alloc:1;
>   	u8		 lname_alloc:1;
> +	u8		 is_64_bit:1;
>   	u8		 sorted_by_name;
>   	u8		 loaded;
>   	u8		 rel;
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index eed0b96..a0fc81b 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -595,6 +595,8 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
>   			goto out_elf_end;
>   	}
>
> +	ss->is_64_bit = (gelf_getclass(elf) == ELFCLASS64);
> +
>   	ss->symtab = elf_section_by_name(elf, &ehdr, &ss->symshdr, ".symtab",
>   			NULL);
>   	if (ss->symshdr.sh_type != SHT_SYMTAB)
> @@ -694,6 +696,7 @@ int dso__load_sym(struct dso *dso, struct map *map,
>   	bool remap_kernel = false, adjust_kernel_syms = false;
>
>   	dso->symtab_type = syms_ss->type;
> +	dso->is_64_bit = syms_ss->is_64_bit;
>   	dso->rel = syms_ss->ehdr.e_type == ET_REL;
>
>   	/*
> diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
> index ac7070a..b9d1119 100644
> --- a/tools/perf/util/symbol-minimal.c
> +++ b/tools/perf/util/symbol-minimal.c
> @@ -1,3 +1,4 @@
> +#include "util.h"
>   #include "symbol.h"
>
>   #include <stdio.h>
> @@ -287,6 +288,23 @@ int dso__synthesize_plt_symbols(struct dso *dso __maybe_unused,
>   	return 0;
>   }
>
> +static int fd__is_64_bit(int fd)
> +{
> +	u8 e_ident[EI_NIDENT];
> +
> +	if (lseek(fd, 0, SEEK_SET))
> +		return -1;
> +
> +	if (readn(fd, e_ident, sizeof(e_ident)) != sizeof(e_ident))
> +		return -1;
> +
> +	if (memcmp(e_ident, ELFMAG, SELFMAG) ||
> +	    e_ident[EI_VERSION] != EV_CURRENT)
> +		return -1;
> +
> +	return e_ident[EI_CLASS] == ELFCLASS64;
> +}
> +
>   int dso__load_sym(struct dso *dso, struct map *map __maybe_unused,
>   		  struct symsrc *ss,
>   		  struct symsrc *runtime_ss __maybe_unused,
> @@ -294,6 +312,11 @@ int dso__load_sym(struct dso *dso, struct map *map __maybe_unused,
>   		  int kmodule __maybe_unused)
>   {
>   	unsigned char *build_id[BUILD_ID_SIZE];
> +	int ret;
> +
> +	ret = fd__is_64_bit(ss->fd);
> +	if (ret >= 0)
> +		dso->is_64_bit = ret;
>
>   	if (filename__read_build_id(ss->name, build_id, BUILD_ID_SIZE) > 0) {
>   		dso__set_build_id(dso, build_id);


Here's what is wrong with this API: you are determining DSO bitness at 
symbol load time, not when the DSO is created and added to the maps.

As I pointed out in a prior comment you are initializing dso->is_64_bit 
to perf's bitness when the dso object is created (dso__new) but the 
value is not correctly set until dso__load time. Some tools (perf-trace) 
never load symbols, so that value is always wrong in the sense that its 
value has no correlation to the dso object.

David
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