[PATCH bpf-next 0/2] libbpf: Support symbol versioning for uprobe

[PATCH bpf-next 0/2] libbpf: Support symbol versioning for uprobe

[Hengqi Chen]

Dynamic symbols in shared library may have the same name, for example:

    $ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
    000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5
    000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34
    000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5

    $ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
      706: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 __pthread_rwlock_wrlock@GLIBC_2.2.5
      2568: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@@GLIBC_2.34
      2571: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@GLIBC_2.2.5

There are two pthread_rwlock_wrlock symbols in .dynsym section of libc.
The one with @@ is the default version, the other is hidden.
Note that the version info is actually stored in .gnu.version and .gnu.version_d
sections of libc and the two symbols are at the same offset.

Currently, specify `pthread_rwlock_wrlock`, `pthread_rwlock_wrlock@@GLIBC_2.34`
or `pthread_rwlock_wrlock@GLIBC_2.2.5` in bpf_uprobe_opts::func_name won't work.
Because there are two `pthread_rwlock_wrlock` in .dynsym sections without the
version suffix and both are global bind.

This patchset adds symbol versioning ([0]) support for dynsym for uprobe,
so that we can handle the above case.

  [0]: https://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA.junk/symversion.html

Hengqi Chen (2):
  libbpf: Resolve ambiguous matches at the same offset for uprobe
  libbpf: Support symbol versioning for uprobe

 tools/lib/bpf/elf.c | 103 ++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 94 insertions(+), 9 deletions(-)

--
2.39.3

[PATCH bpf-next 1/2] libbpf: Resolve ambiguous matches at the same offset for uprobe

[Hengqi Chen]

Dynamic symbols in shared library may have the same name, for example:

    $ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
    000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5
    000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34
    000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5

    $ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
     706: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 __pthread_rwlock_wrlock@GLIBC_2.2.5
    2568: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@@GLIBC_2.34
    2571: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@GLIBC_2.2.5

Currently, we can't attach a uprobe to pthread_rwlock_wrlock because
both symbols are global bind. Since both of them are at the same offset
we could accept one of them harmlessly.

Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
---
 tools/lib/bpf/elf.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c
index 9d0296c1726a..5c9e588b17da 100644
--- a/tools/lib/bpf/elf.c
+++ b/tools/lib/bpf/elf.c
@@ -214,7 +214,10 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)

 			if (ret > 0) {
 				/* handle multiple matches */
-				if (last_bind != STB_WEAK && cur_bind != STB_WEAK) {
+				if (elf_sym_offset(sym) == ret) {
+					/* same offset, no problem */
+					continue;
+				} else if (last_bind != STB_WEAK && cur_bind != STB_WEAK) {
 					/* Only accept one non-weak bind. */
 					pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
 						sym->name, name, binary_path);
--
2.39.3

[PATCH bpf-next 2/2] libbpf: Support symbol versioning for uprobe

[Hengqi Chen]

Currently, we allow users to specify symbol name for uprobe in a qualified
form, i.e. func@@LIB or func@@LIB_VERSION. For dynamic symbols, their version
info is actually stored in .gnu.version and .gnu.version_d sections of the ELF
objects. So dynamic symbols and the qualified name won't match. Add support for
symbol versioning ([0]) so that we can handle the above case.

  [0]: https://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA.junk/symversion.html

Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
---
 tools/lib/bpf/elf.c | 98 +++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 90 insertions(+), 8 deletions(-)

diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c
index 5c9e588b17da..ed3d9880eaa4 100644
--- a/tools/lib/bpf/elf.c
+++ b/tools/lib/bpf/elf.c
@@ -9,6 +9,7 @@
 #include "str_error.h"

 #define STRERR_BUFSIZE  128
+#define HIDDEN_BIT	16

 int elf_open(const char *binary_path, struct elf_fd *elf_fd)
 {
@@ -64,11 +65,14 @@ struct elf_sym {
 	const char *name;
 	GElf_Sym sym;
 	GElf_Shdr sh;
+	int ver;
+	bool hidden;
 };

 struct elf_sym_iter {
 	Elf *elf;
 	Elf_Data *syms;
+	Elf_Data *versyms;
 	size_t nr_syms;
 	size_t strtabidx;
 	size_t next_sym_idx;
@@ -111,6 +115,18 @@ static int elf_sym_iter_new(struct elf_sym_iter *iter,
 	iter->nr_syms = iter->syms->d_size / sh.sh_entsize;
 	iter->elf = elf;
 	iter->st_type = st_type;
+
+	/* Version symbol table only meaningful to dynsym only */
+	if (sh_type != SHT_DYNSYM)
+		return 0;
+
+	scn = elf_find_next_scn_by_type(elf, SHT_GNU_versym, NULL);
+	if (!scn)
+		return 0;
+	if (!gelf_getshdr(scn, &sh))
+		return -EINVAL;
+	iter->versyms = elf_getdata(scn, 0);
+
 	return 0;
 }

@@ -119,6 +135,7 @@ static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)
 	struct elf_sym *ret = &iter->sym;
 	GElf_Sym *sym = &ret->sym;
 	const char *name = NULL;
+	GElf_Versym versym;
 	Elf_Scn *sym_scn;
 	size_t idx;

@@ -138,12 +155,57 @@ static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)

 		iter->next_sym_idx = idx + 1;
 		ret->name = name;
+		ret->ver = 0;
+		ret->hidden = false;
+
+		if (iter->versyms) {
+			if (!gelf_getversym(iter->versyms, idx, &versym))
+				continue;
+			ret->ver = versym & ~(1 << HIDDEN_BIT);
+			ret->hidden = versym & (1 << HIDDEN_BIT);
+		}
 		return ret;
 	}

 	return NULL;
 }

+static const char *elf_get_vername(Elf *elf, int ver)
+{
+	GElf_Verdaux verdaux;
+	GElf_Verdef verdef;
+	Elf_Data *verdefs;
+	size_t strtabidx;
+	GElf_Shdr sh;
+	Elf_Scn *scn;
+	int offset;
+
+	scn = elf_find_next_scn_by_type(elf, SHT_GNU_verdef, NULL);
+	if (!scn)
+		return NULL;
+	if (!gelf_getshdr(scn, &sh))
+		return NULL;
+	strtabidx = sh.sh_link;
+	verdefs =  elf_getdata(scn, 0);
+
+	offset = 0;
+	while (gelf_getverdef(verdefs, offset, &verdef)) {
+		if (verdef.vd_ndx != ver) {
+			if (!verdef.vd_next)
+				break;
+
+			offset += verdef.vd_next;
+			continue;
+		}
+
+		if (!gelf_getverdaux(verdefs, offset + verdef.vd_aux, &verdaux))
+			break;
+
+		return elf_strptr(elf, strtabidx, verdaux.vda_name);
+
+	}
+	return NULL;
+}

 /* Transform symbol's virtual address (absolute for binaries and relative
  * for shared libs) into file offset, which is what kernel is expecting
@@ -191,6 +253,9 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
 	for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
 		struct elf_sym_iter iter;
 		struct elf_sym *sym;
+		size_t sname_len;
+		char sname[256];
+		const char *ver;
 		int last_bind = -1;
 		int cur_bind;

@@ -201,14 +266,31 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
 			goto out;

 		while ((sym = elf_sym_iter_next(&iter))) {
-			/* User can specify func, func@@LIB or func@@LIB_VERSION. */
-			if (strncmp(sym->name, name, name_len) != 0)
-				continue;
-			/* ...but we don't want a search for "foo" to match 'foo2" also, so any
-			 * additional characters in sname should be of the form "@@LIB".
-			 */
-			if (!is_name_qualified && sym->name[name_len] != '\0' && sym->name[name_len] != '@')
-				continue;
+			if (sh_types[i] == SHT_DYNSYM && is_name_qualified) {
+				if (sym->hidden)
+					continue;
+
+				sname_len = strlen(sym->name);
+				if (strncmp(sym->name, name, sname_len) != 0)
+					continue;
+
+				ver = elf_get_vername(elf, sym->ver);
+				if (!ver)
+					continue;
+
+				snprintf(sname, sizeof(sname), "%s@@%s", sym->name, ver);
+				if (strncmp(sname, name, name_len) != 0)
+					continue;
+			} else {
+				/* User can specify func, func@@LIB or func@@LIB_VERSION. */
+				if (strncmp(sym->name, name, name_len) != 0)
+					continue;
+				/* ...but we don't want a search for "foo" to match 'foo2" also, so any
+				* additional characters in sname should be of the form "@@LIB".
+				*/
+				if (!is_name_qualified && sym->name[name_len] != '\0' && sym->name[name_len] != '@')
+					continue;
+			}

 			cur_bind = GELF_ST_BIND(sym->sym.st_info);

--
2.39.3

Re: [PATCH bpf-next 2/2] libbpf: Support symbol versioning for uprobe

[Jiri Olsa]

On Mon, Sep 04, 2023 at 02:24:44AM +0000, Hengqi Chen wrote:
> Currently, we allow users to specify symbol name for uprobe in a qualified
> form, i.e. func@@LIB or func@@LIB_VERSION. For dynamic symbols, their version
> info is actually stored in .gnu.version and .gnu.version_d sections of the ELF
> objects. So dynamic symbols and the qualified name won't match. Add support for
> symbol versioning ([0]) so that we can handle the above case.
> 
>   [0]: https://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA.junk/symversion.html
> 
> Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
> ---
>  tools/lib/bpf/elf.c | 98 +++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 90 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c
> index 5c9e588b17da..ed3d9880eaa4 100644
> --- a/tools/lib/bpf/elf.c
> +++ b/tools/lib/bpf/elf.c
> @@ -9,6 +9,7 @@
>  #include "str_error.h"
> 
>  #define STRERR_BUFSIZE  128
> +#define HIDDEN_BIT	16

hum, the docs says it's bit 15 ?

SNIP

> @@ -138,12 +155,57 @@ static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)
> 
>  		iter->next_sym_idx = idx + 1;
>  		ret->name = name;
> +		ret->ver = 0;
> +		ret->hidden = false;
> +
> +		if (iter->versyms) {
> +			if (!gelf_getversym(iter->versyms, idx, &versym))
> +				continue;
> +			ret->ver = versym & ~(1 << HIDDEN_BIT);
> +			ret->hidden = versym & (1 << HIDDEN_BIT);
> +		}
>  		return ret;
>  	}
> 
>  	return NULL;
>  }
> 
> +static const char *elf_get_vername(Elf *elf, int ver)
> +{
> +	GElf_Verdaux verdaux;
> +	GElf_Verdef verdef;
> +	Elf_Data *verdefs;
> +	size_t strtabidx;
> +	GElf_Shdr sh;
> +	Elf_Scn *scn;
> +	int offset;
> +
> +	scn = elf_find_next_scn_by_type(elf, SHT_GNU_verdef, NULL);
> +	if (!scn)
> +		return NULL;
> +	if (!gelf_getshdr(scn, &sh))
> +		return NULL;
> +	strtabidx = sh.sh_link;
> +	verdefs =  elf_getdata(scn, 0);

should we read verdefs same as you did for versyms in elf_sym_iter_new,
so you don't need to read that every time?

> +
> +	offset = 0;
> +	while (gelf_getverdef(verdefs, offset, &verdef)) {
> +		if (verdef.vd_ndx != ver) {
> +			if (!verdef.vd_next)
> +				break;
> +
> +			offset += verdef.vd_next;
> +			continue;
> +		}
> +
> +		if (!gelf_getverdaux(verdefs, offset + verdef.vd_aux, &verdaux))
> +			break;
> +
> +		return elf_strptr(elf, strtabidx, verdaux.vda_name);
> +
> +	}
> +	return NULL;
> +}
> 
>  /* Transform symbol's virtual address (absolute for binaries and relative
>   * for shared libs) into file offset, which is what kernel is expecting
> @@ -191,6 +253,9 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
>  	for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
>  		struct elf_sym_iter iter;
>  		struct elf_sym *sym;
> +		size_t sname_len;
> +		char sname[256];

is this enough? not sure if there's symbol max size,
maybe we could also use asprintf below

> +		const char *ver;
>  		int last_bind = -1;
>  		int cur_bind;
> 
> @@ -201,14 +266,31 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
>  			goto out;
> 
>  		while ((sym = elf_sym_iter_next(&iter))) {
> -			/* User can specify func, func@@LIB or func@@LIB_VERSION. */
> -			if (strncmp(sym->name, name, name_len) != 0)
> -				continue;
> -			/* ...but we don't want a search for "foo" to match 'foo2" also, so any
> -			 * additional characters in sname should be of the form "@@LIB".
> -			 */
> -			if (!is_name_qualified && sym->name[name_len] != '\0' && sym->name[name_len] != '@')
> -				continue;
> +			if (sh_types[i] == SHT_DYNSYM && is_name_qualified) {
> +				if (sym->hidden)
> +					continue;
> +
> +				sname_len = strlen(sym->name);
> +				if (strncmp(sym->name, name, sname_len) != 0)
> +					continue;
> +
> +				ver = elf_get_vername(elf, sym->ver);
> +				if (!ver)
> +					continue;
> +
> +				snprintf(sname, sizeof(sname), "%s@@%s", sym->name, ver);
> +				if (strncmp(sname, name, name_len) != 0)
> +					continue;
> +			} else {
> +				/* User can specify func, func@@LIB or func@@LIB_VERSION. */
> +				if (strncmp(sym->name, name, name_len) != 0)
> +					continue;
> +				/* ...but we don't want a search for "foo" to match 'foo2" also, so any
> +				* additional characters in sname should be of the form "@@LIB".
> +				*/
> +				if (!is_name_qualified && sym->name[name_len] != '\0' && sym->name[name_len] != '@')
> +					continue;

hum, I never checked the versioned symbols, but it looks like we
don't get symbols in 'symbol@version' form, so I wonder how that
worked before

would be great to have a selftest for that

also I had to add change below to test that through prog's section,
I think we need allow '@' in there

thanks,
jirka


---
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 96ff1aa4bf6a..a30f3c48f891 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11512,8 +11512,11 @@ static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf
 
 	*link = NULL;
 
-	n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.]+%li",
+	n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.@]+%li",
 		   &probe_type, &binary_path, &func_name, &offset);

Re: [PATCH bpf-next 2/2] libbpf: Support symbol versioning for uprobe

[Hengqi Chen]

Hi, Jiri:

On 9/4/23 22:10, Jiri Olsa wrote:
> On Mon, Sep 04, 2023 at 02:24:44AM +0000, Hengqi Chen wrote:
>> Currently, we allow users to specify symbol name for uprobe in a qualified
>> form, i.e. func@@LIB or func@@LIB_VERSION. For dynamic symbols, their version
>> info is actually stored in .gnu.version and .gnu.version_d sections of the ELF
>> objects. So dynamic symbols and the qualified name won't match. Add support for
>> symbol versioning ([0]) so that we can handle the above case.
>>
>>   [0]: https://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA.junk/symversion.html
>>
>> Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
>> ---
>>  tools/lib/bpf/elf.c | 98 +++++++++++++++++++++++++++++++++++++++++----
>>  1 file changed, 90 insertions(+), 8 deletions(-)
>>
>> diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c
>> index 5c9e588b17da..ed3d9880eaa4 100644
>> --- a/tools/lib/bpf/elf.c
>> +++ b/tools/lib/bpf/elf.c
>> @@ -9,6 +9,7 @@
>>  #include "str_error.h"
>>
>>  #define STRERR_BUFSIZE  128
>> +#define HIDDEN_BIT	16
> 
> hum, the docs says it's bit 15 ?

Ahh, right, should be 15.

> 
> SNIP
> 
>> @@ -138,12 +155,57 @@ static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)
>>
>>  		iter->next_sym_idx = idx + 1;
>>  		ret->name = name;
>> +		ret->ver = 0;
>> +		ret->hidden = false;
>> +
>> +		if (iter->versyms) {
>> +			if (!gelf_getversym(iter->versyms, idx, &versym))
>> +				continue;
>> +			ret->ver = versym & ~(1 << HIDDEN_BIT);
>> +			ret->hidden = versym & (1 << HIDDEN_BIT);
>> +		}
>>  		return ret;
>>  	}
>>
>>  	return NULL;
>>  }
>>
>> +static const char *elf_get_vername(Elf *elf, int ver)
>> +{
>> +	GElf_Verdaux verdaux;
>> +	GElf_Verdef verdef;
>> +	Elf_Data *verdefs;
>> +	size_t strtabidx;
>> +	GElf_Shdr sh;
>> +	Elf_Scn *scn;
>> +	int offset;
>> +
>> +	scn = elf_find_next_scn_by_type(elf, SHT_GNU_verdef, NULL);
>> +	if (!scn)
>> +		return NULL;
>> +	if (!gelf_getshdr(scn, &sh))
>> +		return NULL;
>> +	strtabidx = sh.sh_link;
>> +	verdefs =  elf_getdata(scn, 0);
> 
> should we read verdefs same as you did for versyms in elf_sym_iter_new,
> so you don't need to read that every time?
> 

It looks weird to retrieve version from elf_sym_iter, and we should not
reach here too many times.

>> +
>> +	offset = 0;
>> +	while (gelf_getverdef(verdefs, offset, &verdef)) {
>> +		if (verdef.vd_ndx != ver) {
>> +			if (!verdef.vd_next)
>> +				break;
>> +
>> +			offset += verdef.vd_next;
>> +			continue;
>> +		}
>> +
>> +		if (!gelf_getverdaux(verdefs, offset + verdef.vd_aux, &verdaux))
>> +			break;
>> +
>> +		return elf_strptr(elf, strtabidx, verdaux.vda_name);
>> +
>> +	}
>> +	return NULL;
>> +}
>>
>>  /* Transform symbol's virtual address (absolute for binaries and relative
>>   * for shared libs) into file offset, which is what kernel is expecting
>> @@ -191,6 +253,9 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
>>  	for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
>>  		struct elf_sym_iter iter;
>>  		struct elf_sym *sym;
>> +		size_t sname_len;
>> +		char sname[256];
> 
> is this enough? not sure if there's symbol max size,
> maybe we could also use asprintf below
> 

OK, will use asprintf instead.

>> +		const char *ver;
>>  		int last_bind = -1;
>>  		int cur_bind;
>>
>> @@ -201,14 +266,31 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
>>  			goto out;
>>
>>  		while ((sym = elf_sym_iter_next(&iter))) {
>> -			/* User can specify func, func@@LIB or func@@LIB_VERSION. */
>> -			if (strncmp(sym->name, name, name_len) != 0)
>> -				continue;
>> -			/* ...but we don't want a search for "foo" to match 'foo2" also, so any
>> -			 * additional characters in sname should be of the form "@@LIB".
>> -			 */
>> -			if (!is_name_qualified && sym->name[name_len] != '\0' && sym->name[name_len] != '@')
>> -				continue;
>> +			if (sh_types[i] == SHT_DYNSYM && is_name_qualified) {
>> +				if (sym->hidden)
>> +					continue;
>> +
>> +				sname_len = strlen(sym->name);
>> +				if (strncmp(sym->name, name, sname_len) != 0)
>> +					continue;
>> +
>> +				ver = elf_get_vername(elf, sym->ver);
>> +				if (!ver)
>> +					continue;
>> +
>> +				snprintf(sname, sizeof(sname), "%s@@%s", sym->name, ver);
>> +				if (strncmp(sname, name, name_len) != 0)
>> +					continue;
>> +			} else {
>> +				/* User can specify func, func@@LIB or func@@LIB_VERSION. */
>> +				if (strncmp(sym->name, name, name_len) != 0)
>> +					continue;
>> +				/* ...but we don't want a search for "foo" to match 'foo2" also, so any
>> +				* additional characters in sname should be of the form "@@LIB".
>> +				*/
>> +				if (!is_name_qualified && sym->name[name_len] != '\0' && sym->name[name_len] != '@')
>> +					continue;
> 
> hum, I never checked the versioned symbols, but it looks like we
> don't get symbols in 'symbol@version' form, so I wonder how that
> worked before
> 
> would be great to have a selftest for that
> 
> also I had to add change below to test that through prog's section,
> I think we need allow '@' in there
> 

Let me try.

> thanks,
> jirka
> 
> 
> ---
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 96ff1aa4bf6a..a30f3c48f891 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -11512,8 +11512,11 @@ static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf
>  
>  	*link = NULL;
>  
> -	n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.]+%li",
> +	n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.@]+%li",
>  		   &probe_type, &binary_path, &func_name, &offset);

---
Hengqi

Re: [PATCH bpf-next 0/2] libbpf: Support symbol versioning for uprobe

[Alan Maguire]

On 04/09/2023 03:24, Hengqi Chen wrote:
> Dynamic symbols in shared library may have the same name, for example:
> 
>     $ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
>     000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5
>     000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34
>     000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5
> 
>     $ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
>       706: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 __pthread_rwlock_wrlock@GLIBC_2.2.5
>       2568: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@@GLIBC_2.34
>       2571: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@GLIBC_2.2.5
> 
> There are two pthread_rwlock_wrlock symbols in .dynsym section of libc.
> The one with @@ is the default version, the other is hidden.
> Note that the version info is actually stored in .gnu.version and .gnu.version_d
> sections of libc and the two symbols are at the same offset.
> 
> Currently, specify `pthread_rwlock_wrlock`, `pthread_rwlock_wrlock@@GLIBC_2.34`
> or `pthread_rwlock_wrlock@GLIBC_2.2.5` in bpf_uprobe_opts::func_name won't work.
> Because there are two `pthread_rwlock_wrlock` in .dynsym sections without the
> version suffix and both are global bind.
> 
> This patchset adds symbol versioning ([0]) support for dynsym for uprobe,
> so that we can handle the above case.
>

So it looks like patch 1 handles the above case for an unqualified
uprobe where the addresses match; is there a reasonable approach to
take for the unqualified version case where the addresses for different
global symbol versions do not match (such as "use the most recent
version")? Thanks!

Alan

>   [0]: https://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA.junk/symversion.html
> 
> Hengqi Chen (2):
>   libbpf: Resolve ambiguous matches at the same offset for uprobe
>   libbpf: Support symbol versioning for uprobe
> 
>  tools/lib/bpf/elf.c | 103 ++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 94 insertions(+), 9 deletions(-)
> 
> --
> 2.39.3
> 

Re: [PATCH bpf-next 0/2] libbpf: Support symbol versioning for uprobe

[Hengqi Chen]

Hi, Alan:

On 9/4/23 16:38, Alan Maguire wrote:
> On 04/09/2023 03:24, Hengqi Chen wrote:
>> Dynamic symbols in shared library may have the same name, for example:
>>
>>     $ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
>>     000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5
>>     000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34
>>     000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5
>>
>>     $ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
>>       706: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 __pthread_rwlock_wrlock@GLIBC_2.2.5
>>       2568: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@@GLIBC_2.34
>>       2571: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@GLIBC_2.2.5
>>
>> There are two pthread_rwlock_wrlock symbols in .dynsym section of libc.
>> The one with @@ is the default version, the other is hidden.
>> Note that the version info is actually stored in .gnu.version and .gnu.version_d
>> sections of libc and the two symbols are at the same offset.
>>
>> Currently, specify `pthread_rwlock_wrlock`, `pthread_rwlock_wrlock@@GLIBC_2.34`
>> or `pthread_rwlock_wrlock@GLIBC_2.2.5` in bpf_uprobe_opts::func_name won't work.
>> Because there are two `pthread_rwlock_wrlock` in .dynsym sections without the
>> version suffix and both are global bind.
>>
>> This patchset adds symbol versioning ([0]) support for dynsym for uprobe,
>> so that we can handle the above case.
>>
> 
> So it looks like patch 1 handles the above case for an unqualified
> uprobe where the addresses match; is there a reasonable approach to

Yes.

> take for the unqualified version case where the addresses for different
> global symbol versions do not match (such as "use the most recent
> version")? Thanks!
> 

No ideas, need further investigations.
For such cases, I guess users should specify func@LIB_VERSION.

> Alan
> 
>>   [0]: https://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA.junk/symversion.html
>>
>> Hengqi Chen (2):
>>   libbpf: Resolve ambiguous matches at the same offset for uprobe
>>   libbpf: Support symbol versioning for uprobe
>>
>>  tools/lib/bpf/elf.c | 103 ++++++++++++++++++++++++++++++++++++++++----
>>  1 file changed, 94 insertions(+), 9 deletions(-)
>>
>> --
>> 2.39.3
>>

---
Hengqi