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libbpf-tools: support to find symbols in different mount namespace #4854

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libbpf-tools: support to find symbols in different mount namespace #4854

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267 changes: 256 additions & 11 deletions libbpf-tools/trace_helpers.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
// 28-Feb-2020 Wenbo Zhang Created this.
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#include <sched.h>
#endif
#include <ctype.h>
#include <inttypes.h>
Expand All @@ -15,6 +16,7 @@
#include <errno.h>
#include <fcntl.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <time.h>
#include <bpf/bpf.h>
#include <bpf/btf.h>
Expand Down Expand Up @@ -228,6 +230,7 @@ struct map {
};

struct syms {
struct nsinfo *nsi;
struct dso *dsos;
int dso_sz;
};
Expand Down Expand Up @@ -320,6 +323,220 @@ static int get_elf_text_scn_info(const char *path, uint64_t *addr,
return err;
}

/*
* The following code related to nsinfo is based on the code of perf, see:
* https://github.com/torvalds/linux/commit/843ff37bb59edbe51d64e77ba1b3245a15a4dd9f
*/
struct nscookie {
int oldns;
int newns;
char *oldcwd;
};

struct nsinfo {
pid_t pid;
pid_t tgid;
pid_t nstgid;
bool need_setns;
char *mntns_path;
};

static pid_t nsinfo__pid(const struct nsinfo *nsi)
{
return nsi->pid;
}

static inline void nsinfo__clear_need_setns(struct nsinfo *nsi)
{
nsi->need_setns = false;
}

static inline bool nsinfo__need_setns(struct nsinfo *nsi)
{
return nsi->need_setns;
}

static inline const char *nsinfo__mntns_path(const struct nsinfo *nsi)
{
return nsi->mntns_path;
}

static int nsinfo__get_nspid(pid_t *tgid, pid_t *nstgid, const char *path)
{
FILE *f = NULL;
char *statln = NULL;
size_t linesz = 0;
char *nspid;

f = fopen(path, "r");
if (f == NULL)
return -1;

while (getline(&statln, &linesz, f) != -1) {
/* Use tgid if CONFIG_PID_NS is not defined. */
if (strstr(statln, "Tgid:") != NULL) {
*tgid = (pid_t)strtol(strrchr(statln, '\t'), NULL, 10);
*nstgid = *tgid;
}

if (strstr(statln, "NStgid:") != NULL) {
nspid = strrchr(statln, '\t');
*nstgid = (pid_t)strtol(nspid, NULL, 10);
break;
}
}

fclose(f);
free(statln);
return 0;
}

static int nsinfo__init(struct nsinfo *nsi)
{
char oldns[PATH_MAX];
char spath[PATH_MAX];
struct stat old_stat;
struct stat new_stat;
char *newns = NULL;
int rv = -1;

if (snprintf(oldns, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
return rv;

if (asprintf(&newns, "/proc/%d/ns/mnt", nsi->pid) == -1)
return rv;

if (stat(oldns, &old_stat) < 0)
goto out;

if (stat(newns, &new_stat) < 0)
goto out;

/* Check if the mount namespaces differ, if so then indicate that we
* want to switch as part of looking up dso/map data.
*/
if (old_stat.st_ino != new_stat.st_ino) {
nsi->need_setns = true;
nsi->mntns_path = newns;
newns = NULL;
}

/* If we're dealing with a process that is in a different PID namespace,
* attempt to work out the innermost tgid for the process.
*/
if (snprintf(spath, PATH_MAX, "/proc/%d/status", nsinfo__pid(nsi)) >= PATH_MAX)
goto out;

rv = nsinfo__get_nspid(&nsi->tgid, &nsi->nstgid, spath);

out:
free(newns);
return rv;
}

static struct nsinfo *nsinfo__new(pid_t pid)
{
struct nsinfo *nsi;

if (pid == 0)
return NULL;

nsi = calloc(1, sizeof(*nsi));
if (!nsi)
return NULL;
nsi->pid = pid;

/* Init may fail if the process exits while we're trying to look at its
* proc information. In that case, save the pid but don't try to enter
* the namespace.
*/
if (nsinfo__init(nsi) < 0) {
nsinfo__clear_need_setns(nsi);
}

return nsi;
}

static void nsinfo__free(struct nsinfo *nsi)
{
if (nsi) {
free(nsi->mntns_path);
free(nsi);
}
}

static void nsinfo__mountns_enter(struct nsinfo *nsi, struct nscookie *nc)
{
char curpath[PATH_MAX];
int oldns = -1;
int newns = -1;
char *oldcwd = NULL;

if (nc == NULL)
return;

nc->oldns = -1;
nc->newns = -1;

if (!nsi || !nsinfo__need_setns(nsi))
return;

if (snprintf(curpath, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
return;

oldcwd = get_current_dir_name();
if (!oldcwd)
return;

oldns = open(curpath, O_RDONLY);
if (oldns < 0)
goto errout;

newns = open(nsinfo__mntns_path(nsi), O_RDONLY);
if (newns < 0)
goto errout;

if (setns(newns, CLONE_NEWNS) < 0)
goto errout;

nc->oldcwd = oldcwd;
nc->oldns = oldns;
nc->newns = newns;

return;

errout:
free(oldcwd);
if (oldns > -1)
close(oldns);
if (newns > -1)
close(newns);
}

static void nsinfo__mountns_exit(struct nscookie *nc)
{
if (nc == NULL || nc->oldns == -1 || nc->newns == -1 || !nc->oldcwd)
return;

setns(nc->oldns, CLONE_NEWNS);

if (nc->oldcwd) {
chdir(nc->oldcwd);
free(nc->oldcwd);
nc->oldcwd = NULL;
}

if (nc->oldns > -1) {
close(nc->oldns);
nc->oldns = -1;
}

if (nc->newns > -1) {
close(nc->newns);
nc->newns = -1;
}
}

static int syms__add_dso(struct syms *syms, struct map *map, const char *name)
{
struct dso *dso = NULL;
Expand Down Expand Up @@ -493,15 +710,19 @@ static void dso__free_fields(struct dso *dso)
btf__free(dso->btf);
}

static int dso__load_sym_table_from_elf(struct dso *dso, int fd)
static int dso__load_sym_table_from_elf(struct dso *dso, struct nsinfo *nsi, int fd)
{
Elf_Scn *section = NULL;
struct nscookie nsc;
Elf *e;
int i;

nsinfo__mountns_enter(nsi, &nsc);
e = fd > 0 ? open_elf_by_fd(fd) : open_elf(dso->name, &fd);
if (!e)
if (!e) {
nsinfo__mountns_exit(&nsc);
return -1;
}

while ((section = elf_nextscn(e, section)) != 0) {
GElf_Shdr header;
Expand All @@ -527,11 +748,13 @@ static int dso__load_sym_table_from_elf(struct dso *dso, int fd)
qsort(dso->syms, dso->syms_sz, sizeof(*dso->syms), sym_cmp);

close_elf(e, fd);
nsinfo__mountns_exit(&nsc);
return 0;

err_out:
dso__free_fields(dso);
close_elf(e, fd);
nsinfo__mountns_exit(&nsc);
return -1;
}

Expand Down Expand Up @@ -608,28 +831,28 @@ static int dso__load_sym_table_from_vdso_image(struct dso *dso)

if (fd < 0)
return -1;
return dso__load_sym_table_from_elf(dso, fd);
return dso__load_sym_table_from_elf(dso, NULL, fd);
}

static int dso__load_sym_table(struct dso *dso)
static int dso__load_sym_table(struct dso *dso, struct nsinfo *nsi)
{
if (dso->type == UNKNOWN)
return -1;
if (dso->type == PERF_MAP)
return dso__load_sym_table_from_perf_map(dso);
if (dso->type == EXEC || dso->type == DYN)
return dso__load_sym_table_from_elf(dso, 0);
return dso__load_sym_table_from_elf(dso, nsi, 0);
if (dso->type == VDSO)
return dso__load_sym_table_from_vdso_image(dso);
return -1;
}

static struct sym *dso__find_sym(struct dso *dso, uint64_t offset)
static struct sym *dso__find_sym(struct dso *dso, struct nsinfo *nsi, uint64_t offset)
{
unsigned long sym_addr;
int start, end, mid;

if (!dso->syms && dso__load_sym_table(dso))
if (!dso->syms && dso__load_sym_table(dso, nsi))
return NULL;

start = 0;
Expand Down Expand Up @@ -706,12 +929,33 @@ struct syms *syms__load_file(const char *fname)
return NULL;
}

static void fill_map_file_name(char *fname, size_t len, struct nsinfo *nsi)
{
pid_t tgid = nsi->tgid;

if (nsi->need_setns) {
tgid = nsi->nstgid;
}
snprintf(fname, len, "/proc/%ld/maps", (long)tgid);
}

struct syms *syms__load_pid(pid_t tgid)
{
struct nscookie nsc;
struct nsinfo *nsi;
struct syms *syms;
char fname[128];

snprintf(fname, sizeof(fname), "/proc/%ld/maps", (long)tgid);
return syms__load_file(fname);
nsi = nsinfo__new(tgid);
if (!nsi)
return NULL;

nsinfo__mountns_enter(nsi, &nsc);
fill_map_file_name(fname,sizeof(fname), nsi);
syms = syms__load_file(fname);
nsinfo__mountns_exit(&nsc);
syms->nsi = nsi;
return syms;
}

void syms__free(struct syms *syms)
Expand All @@ -723,6 +967,7 @@ void syms__free(struct syms *syms)

for (i = 0; i < syms->dso_sz; i++)
dso__free_fields(&syms->dsos[i]);
nsinfo__free(syms->nsi);
free(syms->dsos);
free(syms);
}
Expand All @@ -735,7 +980,7 @@ const struct sym *syms__map_addr(const struct syms *syms, unsigned long addr)
dso = syms__find_dso(syms, addr, &offset);
if (!dso)
return NULL;
return dso__find_sym(dso, offset);
return dso__find_sym(dso, syms->nsi, offset);
}

const struct sym *syms__map_addr_dso(const struct syms *syms, unsigned long addr,
Expand All @@ -751,7 +996,7 @@ const struct sym *syms__map_addr_dso(const struct syms *syms, unsigned long addr
*dso_name = dso->name;
*dso_offset = offset;

return dso__find_sym(dso, offset);
return dso__find_sym(dso, syms->nsi, offset);
}

struct syms_cache {
Expand Down
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