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libbpf: Fix uprobe offset calculation #8647

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libbpf: Fix uprobe offset calculation #8647

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32 changes: 24 additions & 8 deletions tools/lib/bpf/elf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -260,13 +260,29 @@ static bool symbol_match(struct elf_sym_iter *iter, int sh_type, struct elf_sym
* for shared libs) into file offset, which is what kernel is expecting
* for uprobe/uretprobe attachment.
* See Documentation/trace/uprobetracer.rst for more details. This is done
* by looking up symbol's containing section's header and using iter's virtual
* address (sh_addr) and corresponding file offset (sh_offset) to transform
* by looking up symbol's containing program header and using its virtual
* address (p_vaddr) and corresponding file offset (p_offset) to transform
* sym.st_value (virtual address) into desired final file offset.
*/
static unsigned long elf_sym_offset(struct elf_sym *sym)
static unsigned long elf_sym_offset(Elf *elf, struct elf_sym *sym)
{
return sym->sym.st_value - sym->sh.sh_addr + sym->sh.sh_offset;
size_t nhdrs, i;
GElf_Phdr phdr;

if (elf_getphdrnum(elf, &nhdrs))
return -1;

for (i = 0; i < nhdrs; i++) {
if (!gelf_getphdr(elf, (int)i, &phdr))
continue;
if (phdr.p_type != PT_LOAD)
continue;
if (sym->sym.st_value >= phdr.p_vaddr &&
sym->sym.st_value < (phdr.p_vaddr + phdr.p_memsz))
return sym->sym.st_value - phdr.p_vaddr + phdr.p_offset;
}

return -1;
}

/* Find offset of function name in the provided ELF object. "binary_path" is
Expand Down Expand Up @@ -329,7 +345,7 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)

if (ret > 0) {
/* handle multiple matches */
if (elf_sym_offset(sym) == ret) {
if (elf_sym_offset(elf, sym) == ret) {
/* same offset, no problem */
continue;
} else if (last_bind != STB_WEAK && cur_bind != STB_WEAK) {
Expand All @@ -346,7 +362,7 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
}
}

ret = elf_sym_offset(sym);
ret = elf_sym_offset(elf, sym);
last_bind = cur_bind;
}
if (ret > 0)
Expand Down Expand Up @@ -445,7 +461,7 @@ int elf_resolve_syms_offsets(const char *binary_path, int cnt,
goto out;

while ((sym = elf_sym_iter_next(&iter))) {
unsigned long sym_offset = elf_sym_offset(sym);
unsigned long sym_offset = elf_sym_offset(elf_fd.elf, sym);
int bind = GELF_ST_BIND(sym->sym.st_info);
struct symbol *found, tmp = {
.name = sym->name,
Expand Down Expand Up @@ -534,7 +550,7 @@ int elf_resolve_pattern_offsets(const char *binary_path, const char *pattern,
if (err)
goto out;

offsets[cnt++] = elf_sym_offset(sym);
offsets[cnt++] = elf_sym_offset(elf_fd.elf, sym);
}

/* If we found anything in the first symbol section,
Expand Down
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