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libbpf: Introduce elf_find_func_offset_from_file() function

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This change splits the elf_find_func_offset() function in two:
elf_find_func_offset(), which now accepts an already opened Elf object
instead of a path to a file that is to be opened, as well as
elf_find_func_offset_from_file(), which opens a binary based on a
path and then invokes elf_find_func_offset() on the Elf object. Having
this split in responsibilities will allow us to call
elf_find_func_offset() from other code paths on Elf objects that did not
necessarily come from a file on disk.

Signed-off-by: Daniel Müller <deso@posteo.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230301212308.1839139-3-deso@posteo.net
This commit is contained in:
Daniel Müller
2023-03-01 21:23:07 +00:00
committed by Andrii Nakryiko
parent 9ca6f946cd
commit 47eb62005a
1 changed files with 36 additions and 21 deletions
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57
src/libbpf.c
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@@ -10530,32 +10530,19 @@ static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
return NULL; return NULL;
} }
/* Find offset of function name in object specified by path. "name" matches /* Find offset of function name in the provided ELF object. "binary_path" is
* symbol name or name@@LIB for library functions. * the path to the ELF binary represented by "elf", and only used for error
* reporting matters. "name" matches symbol name or name@@LIB for library
* functions.
*/ */
static long elf_find_func_offset(const char *binary_path, const char *name) static long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
{ {
int fd, i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB }; int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
bool is_shared_lib, is_name_qualified; bool is_shared_lib, is_name_qualified;
char errmsg[STRERR_BUFSIZE];
long ret = -ENOENT; long ret = -ENOENT;
size_t name_len; size_t name_len;
GElf_Ehdr ehdr; GElf_Ehdr ehdr;
Elf *elf;
fd = open(binary_path, O_RDONLY | O_CLOEXEC);
if (fd < 0) {
ret = -errno;
pr_warn("failed to open %s: %s\n", binary_path,
libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
return ret;
}
elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
if (!elf) {
pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
close(fd);
return -LIBBPF_ERRNO__FORMAT;
}
if (!gelf_getehdr(elf, &ehdr)) { if (!gelf_getehdr(elf, &ehdr)) {
pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1)); pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
ret = -LIBBPF_ERRNO__FORMAT; ret = -LIBBPF_ERRNO__FORMAT;
@@ -10568,7 +10555,7 @@ static long elf_find_func_offset(const char *binary_path, const char *name)
/* Does name specify "@@LIB"? */ /* Does name specify "@@LIB"? */
is_name_qualified = strstr(name, "@@") != NULL; is_name_qualified = strstr(name, "@@") != NULL;
/* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if /* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if
* a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically * a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically
* linked binary may not have SHT_DYMSYM, so absence of a section should not be * linked binary may not have SHT_DYMSYM, so absence of a section should not be
* reported as a warning/error. * reported as a warning/error.
@@ -10681,6 +10668,34 @@ static long elf_find_func_offset(const char *binary_path, const char *name)
} }
} }
out: out:
return ret;
}
/* Find offset of function name in ELF object specified by path. "name" matches
* symbol name or name@@LIB for library functions.
*/
static long elf_find_func_offset_from_file(const char *binary_path, const char *name)
{
char errmsg[STRERR_BUFSIZE];
long ret = -ENOENT;
Elf *elf;
int fd;
fd = open(binary_path, O_RDONLY | O_CLOEXEC);
if (fd < 0) {
ret = -errno;
pr_warn("failed to open %s: %s\n", binary_path,
libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
return ret;
}
elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
if (!elf) {
pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
close(fd);
return -LIBBPF_ERRNO__FORMAT;
}
ret = elf_find_func_offset(elf, binary_path, name);
elf_end(elf); elf_end(elf);
close(fd); close(fd);
return ret; return ret;
@@ -10804,7 +10819,7 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
if (func_name) { if (func_name) {
long sym_off; long sym_off;
sym_off = elf_find_func_offset(binary_path, func_name); sym_off = elf_find_func_offset_from_file(binary_path, func_name);
if (sym_off < 0) if (sym_off < 0)
return libbpf_err_ptr(sym_off); return libbpf_err_ptr(sym_off);
func_offset += sym_off; func_offset += sym_off;