diff mbox series

[1/5] Add dso__is_pie call to identify ELF PIE

Message ID 323e931fe9f8f080eb0dfc2e29d112dd7edf1fb2.1724104248.git.scclevenger@os.amperecomputing.com (mailing list archive)
State New, archived
Headers show
Series arm-cs-trace-disasm.py/perf must accommodate non-zero DSO text offset | expand

Commit Message

Steve Clevenger Aug. 20, 2024, 10:11 p.m. UTC 
From: "steve.c.clevenger.ampere" <scclevenger@os.amperecomputing.com>

Add dso__is_pie global to read the .dynamic section DT_FLAGS_1 entry for
the DF_1_PIE flag. This identifies position executable code.
 
Signed-off-by: steve.c.clevenger.ampere <scclevenger@os.amperecomputing.com>
---
 tools/perf/util/symbol-elf.c | 55 ++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

Comments

Leo Yan Aug. 26, 2024, 1:13 p.m. UTC | #1 
Hi Steve,

On Tue, Aug 20, 2024 at 04:11:35PM -0600, Steve Clevenger wrote:
> From: "steve.c.clevenger.ampere" <scclevenger@os.amperecomputing.com>
> 
> Add dso__is_pie global to read the .dynamic section DT_FLAGS_1 entry for
> the DF_1_PIE flag. This identifies position executable code.
>  
> Signed-off-by: steve.c.clevenger.ampere <scclevenger@os.amperecomputing.com>
> ---
>  tools/perf/util/symbol-elf.c | 55 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 55 insertions(+)
> 
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index e398abfd13a0..1d4bd222b314 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -662,6 +662,61 @@ static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf,
>  	return err;
>  }
>  
> +/*
> + * Check dynamic section DT_FLAGS_1 for a Position Independent
> + * Executable (PIE).
> + */
> +bool dso__is_pie(struct dso *dso)
> +{
> +	Elf *elf = NULL;
> +	Elf_Scn *scn = NULL;
> +	GElf_Ehdr ehdr;
> +	GElf_Shdr shdr;
> +	bool is_pie = false;
> +	char dso_path[PATH_MAX];
> +	int fd = -1;
> +
> +	if (!dso || (elf_version(EV_CURRENT) == EV_NONE))
> +		return is_pie;	// false
> +
> +	dso__build_id_filename(dso, dso_path, sizeof(dso_path), false);
> +
> +	fd = open(dso_path, O_RDONLY);
> +
> +	if (fd < 0) {
> +		pr_debug("%s: cannot read cached %s.\n", __func__, dso_path);
> +		return is_pie;	// false
> +	}
> +
> +	elf = elf_begin(fd, ELF_C_READ, NULL);
> +	gelf_getehdr(elf, &ehdr);
> +
> +	if (ehdr.e_type == ET_DYN) {

The code looks good to me, just several nitpicks.

To avoid indentation, we can firstly check the failure case and directly
exit for it.

        if (ehdr.e_type != ET_DYN)
                goto exit_elf_end;

> +		scn = elf_section_by_name(elf, &ehdr, &shdr, ".dynamic", NULL);

Ditto.

        if (!scn)
                goto exit_elf_end;

> +		if (scn) {	// check DT_FLAGS_1
> +			Elf_Data *data;
> +			GElf_Dyn *entry;
> +			int n_entries = shdr.sh_size / sizeof(GElf_Dyn);
> +
> +			data = (Elf_Data *) elf_getdata(scn, NULL);

For a safe code, it is good to check if pointers (data and
data->d_buf) are valid before dereference them.

       if (!data || !data->d_buf)
               goto exit_elf_end;

With above changes:

Reviewed-by: Leo Yan <leo.yan@arm.com>

> +			for (int i = 0; i < n_entries; i++) {
> +				entry = ((GElf_Dyn *) data->d_buf) + i;
> +				if (entry->d_tag == DT_FLAGS_1) {
> +					if ((entry->d_un.d_val & DF_1_PIE) != 0) {
> +						is_pie = true;
> +						break;
> +					}
> +				}
> +			} // end for
> +		}
> +	}
> +
> +	elf_end(elf);
> +	close(fd);
> +
> +	return is_pie;
> +}
> +
>  /*
>   * 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
> -- 
> 2.25.1
> 
>
Steve Clevenger Aug. 26, 2024, 9:33 p.m. UTC | #2 
On 8/26/2024 6:13 AM, Leo Yan wrote:
> Hi Steve,
> 
> On Tue, Aug 20, 2024 at 04:11:35PM -0600, Steve Clevenger wrote:
>> From: "steve.c.clevenger.ampere" <scclevenger@os.amperecomputing.com>
>>
>> Add dso__is_pie global to read the .dynamic section DT_FLAGS_1 entry for
>> the DF_1_PIE flag. This identifies position executable code.
>>  
>> Signed-off-by: steve.c.clevenger.ampere <scclevenger@os.amperecomputing.com>
>> ---
>>  tools/perf/util/symbol-elf.c | 55 ++++++++++++++++++++++++++++++++++++
>>  1 file changed, 55 insertions(+)
>>
>> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
>> index e398abfd13a0..1d4bd222b314 100644
>> --- a/tools/perf/util/symbol-elf.c
>> +++ b/tools/perf/util/symbol-elf.c
>> @@ -662,6 +662,61 @@ static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf,
>>  	return err;
>>  }
>>  
>> +/*
>> + * Check dynamic section DT_FLAGS_1 for a Position Independent
>> + * Executable (PIE).
>> + */
>> +bool dso__is_pie(struct dso *dso)
>> +{
>> +	Elf *elf = NULL;
>> +	Elf_Scn *scn = NULL;
>> +	GElf_Ehdr ehdr;
>> +	GElf_Shdr shdr;
>> +	bool is_pie = false;
>> +	char dso_path[PATH_MAX];
>> +	int fd = -1;
>> +
>> +	if (!dso || (elf_version(EV_CURRENT) == EV_NONE))
>> +		return is_pie;	// false
>> +
>> +	dso__build_id_filename(dso, dso_path, sizeof(dso_path), false);
>> +
>> +	fd = open(dso_path, O_RDONLY);
>> +
>> +	if (fd < 0) {
>> +		pr_debug("%s: cannot read cached %s.\n", __func__, dso_path);
>> +		return is_pie;	// false
>> +	}
>> +
>> +	elf = elf_begin(fd, ELF_C_READ, NULL);
>> +	gelf_getehdr(elf, &ehdr);
>> +
>> +	if (ehdr.e_type == ET_DYN) {
> 
> The code looks good to me, just several nitpicks.
> 
> To avoid indentation, we can firstly check the failure case and directly
> exit for it.
> 
>         if (ehdr.e_type != ET_DYN)
>                 goto exit_elf_end;
> 
>> +		scn = elf_section_by_name(elf, &ehdr, &shdr, ".dynamic", NULL);
> 
> Ditto.
> 
>         if (!scn)
>                 goto exit_elf_end;
> 
>> +		if (scn) {	// check DT_FLAGS_1
>> +			Elf_Data *data;
>> +			GElf_Dyn *entry;
>> +			int n_entries = shdr.sh_size / sizeof(GElf_Dyn);
>> +
>> +			data = (Elf_Data *) elf_getdata(scn, NULL);
> 
> For a safe code, it is good to check if pointers (data and
> data->d_buf) are valid before dereference them.
> 
>        if (!data || !data->d_buf)
>                goto exit_elf_end;
> 
> With above changes:

Thanks Leo. I understand your comment about excess indentation, but I
don't believe there's an excess here. Valid points about NULL pointer
checks. I've made changes based on your review. Please look for V2 of
this patch series. Besides addressing your comments, V2 is mostly to
update the mailing lists.

Steve C.

> 
> Reviewed-by: Leo Yan <leo.yan@arm.com>
> 
>> +			for (int i = 0; i < n_entries; i++) {
>> +				entry = ((GElf_Dyn *) data->d_buf) + i;
>> +				if (entry->d_tag == DT_FLAGS_1) {
>> +					if ((entry->d_un.d_val & DF_1_PIE) != 0) {
>> +						is_pie = true;
>> +						break;
>> +					}
>> +				}
>> +			} // end for
>> +		}
>> +	}
>> +
>> +	elf_end(elf);
>> +	close(fd);
>> +
>> +	return is_pie;
>> +}
>> +
>>  /*
>>   * 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
>> -- 
>> 2.25.1
>>
>>
diff mbox series

Patch

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index e398abfd13a0..1d4bd222b314 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -662,6 +662,61 @@  static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf,
 	return err;
 }
 
+/*
+ * Check dynamic section DT_FLAGS_1 for a Position Independent
+ * Executable (PIE).
+ */
+bool dso__is_pie(struct dso *dso)
+{
+	Elf *elf = NULL;
+	Elf_Scn *scn = NULL;
+	GElf_Ehdr ehdr;
+	GElf_Shdr shdr;
+	bool is_pie = false;
+	char dso_path[PATH_MAX];
+	int fd = -1;
+
+	if (!dso || (elf_version(EV_CURRENT) == EV_NONE))
+		return is_pie;	// false
+
+	dso__build_id_filename(dso, dso_path, sizeof(dso_path), false);
+
+	fd = open(dso_path, O_RDONLY);
+
+	if (fd < 0) {
+		pr_debug("%s: cannot read cached %s.\n", __func__, dso_path);
+		return is_pie;	// false
+	}
+
+	elf = elf_begin(fd, ELF_C_READ, NULL);
+	gelf_getehdr(elf, &ehdr);
+
+	if (ehdr.e_type == ET_DYN) {
+		scn = elf_section_by_name(elf, &ehdr, &shdr, ".dynamic", NULL);
+		if (scn) {	// check DT_FLAGS_1
+			Elf_Data *data;
+			GElf_Dyn *entry;
+			int n_entries = shdr.sh_size / sizeof(GElf_Dyn);
+
+			data = (Elf_Data *) elf_getdata(scn, NULL);
+			for (int i = 0; i < n_entries; i++) {
+				entry = ((GElf_Dyn *) data->d_buf) + i;
+				if (entry->d_tag == DT_FLAGS_1) {
+					if ((entry->d_un.d_val & DF_1_PIE) != 0) {
+						is_pie = true;
+						break;
+					}
+				}
+			} // end for
+		}
+	}
+
+	elf_end(elf);
+	close(fd);
+
+	return is_pie;
+}
+
 /*
  * 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