@@ -651,7 +651,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
printf("search cu '%s' for percpu global variables.\n", cu->name);
cu__for_each_variable(cu, core_id, pos) {
- uint32_t size, type, linkage, offset;
+ uint32_t size, type, linkage;
const char *name;
uint64_t addr;
int id;
@@ -665,12 +665,24 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
/* addr has to be recorded before we follow spec */
addr = var->ip.addr;
- if (var->spec)
- var = var->spec;
+
+ /* DWARF takes into account .data..percpu section offset
+ * within its segment, which for vmlinux is 0, but for kernel
+ * modules is >0. ELF symbols, on the other hand, don't take
+ * into account these offsets (as they are relative to the
+ * section start), so to match DWARF and ELF symbols we need
+ * to negate the section base address here.
+ */
+ if (addr < btfe->percpu_base_addr || addr >= btfe->percpu_base_addr + btfe->percpu_sec_sz)
+ continue;
+ addr -= btfe->percpu_base_addr;
if (!percpu_var_exists(addr, &size, &name))
continue; /* not a per-CPU variable */
+ if (var->spec)
+ var = var->spec;
+
if (var->ip.tag.type == 0) {
fprintf(stderr, "error: found variable '%s' in CU '%s' that has void type\n",
name, cu->name);
@@ -701,8 +713,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
* add a BTF_VAR_SECINFO in btfe->percpu_secinfo, which will be added into
* btfe->types later when we add BTF_VAR_DATASEC.
*/
- offset = addr - btfe->percpu_base_addr;
- id = btf_elf__add_var_secinfo(&btfe->percpu_secinfo, id, offset, size);
+ id = btf_elf__add_var_secinfo(&btfe->percpu_secinfo, id, addr, size);
if (id < 0) {
err = -1;
fprintf(stderr, "error: failed to encode section info for variable '%s' at addr 0x%lx\n",
@@ -170,6 +170,7 @@ try_as_raw_btf:
}
btfe->percpu_shndx = elf_ndxscn(sec);
btfe->percpu_base_addr = shdr.sh_addr;
+ btfe->percpu_sec_sz = shdr.sh_size;
return btfe;
@@ -26,6 +26,7 @@ struct btf_elf {
bool raw_btf; // "/sys/kernel/btf/vmlinux"
uint32_t percpu_shndx;
uint64_t percpu_base_addr;
+ uint64_t percpu_sec_sz;
struct btf *btf;
struct btf *base_btf;
};
Fix pahole's logic for determining per-CPU variables. For vmlinux, btfe->percpu_base_addr is always 0, so it didn't matter at which point to subtract it to get offset that later was matched against corresponding ELF symbol. For kernel module, though, the situation is different. Kernel module's per-CPU data section has non-zero offset, which is taken into account in all DWARF variable addresses calculation. For such cases, it's important to subtract section offset (btfe->percpu_base_addr) before ELF symbol look up is performed. This patch also records per-CPU data section size and uses it for early filtering of non-per-CPU variables by their address. Fixes: 2e719cca6672 ("btf_encoder: revamp how per-CPU variables are encoded") Signed-off-by: Andrii Nakryiko <andrii@kernel.org> --- btf_encoder.c | 21 ++++++++++++++++----- libbtf.c | 1 + libbtf.h | 1 + 3 files changed, 18 insertions(+), 5 deletions(-)