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Use a deterministic hash for USDT symbol names.

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Previously libdtrace used ftok(3), which hashes the inode number of the
input object file.  To increase reproducibility of builds that embed
USDT probes, include a hash of the object file path in the symbol name
instead.

Reported and tested by:	bdrewery
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
This commit is contained in:
Mark Johnston 2020-01-07 21:56:20 +00:00
parent accd6aa25e
commit 938acb0869
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=356477
1 changed files with 22 additions and 5 deletions
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27
cddl/contrib/opensolaris/lib/libdtrace/common/dt_link.c
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@ -57,7 +57,6 @@
#include <sys/mman.h>
#endif
#include <assert.h>
#include <sys/ipc.h>
#include <dt_impl.h>
#include <dt_provider.h>
@ -1249,13 +1248,32 @@ dt_link_error(dtrace_hdl_t *dtp, Elf *elf, int fd, dt_link_pair_t *bufs,
return (dt_set_errno(dtp, EDT_COMPILER));
}
/*
* Provide a unique identifier used when adding global symbols to an object.
* This is the FNV-1a hash of an absolute path for the file.
*/
static unsigned int
hash_obj(const char *obj, int fd)
{
char path[PATH_MAX];
unsigned int h;
if (realpath(obj, path) == NULL)
return (-1);
for (h = 2166136261u, obj = &path[0]; *obj != '\0'; obj++)
h = (h ^ *obj) * 16777619;
h &= 0x7fffffff;
return (h);
}
static int
process_obj(dtrace_hdl_t *dtp, const char *obj, int *eprobesp)
{
static const char dt_prefix[] = "__dtrace";
static const char dt_enabled[] = "enabled";
static const char dt_symprefix[] = "$dtrace";
static const char dt_symfmt[] = "%s%ld.%s";
static const char dt_symfmt[] = "%s%u.%s";
static const char dt_weaksymfmt[] = "%s.%s";
char probename[DTRACE_NAMELEN];
int fd, i, ndx, eprobe, mod = 0;
@ -1272,7 +1290,7 @@ process_obj(dtrace_hdl_t *dtp, const char *obj, int *eprobesp)
dt_probe_t *prp;
uint32_t off, eclass, emachine1, emachine2;
size_t symsize, osym, nsym, isym, istr, len;
key_t objkey;
unsigned int objkey;
dt_link_pair_t *pair, *bufs = NULL;
dt_strtab_t *strtab;
void *tmp;
@ -1350,10 +1368,9 @@ process_obj(dtrace_hdl_t *dtp, const char *obj, int *eprobesp)
* system in order to disambiguate potential conflicts between files of
* the same name which contain identially named local symbols.
*/
if ((objkey = ftok(obj, 0)) == (key_t)-1) {
if ((objkey = hash_obj(obj, fd)) == (unsigned int)-1)
return (dt_link_error(dtp, elf, fd, bufs,
"failed to generate unique key for object file: %s", obj));
}
scn_rel = NULL;
while ((scn_rel = elf_nextscn(elf, scn_rel)) != NULL) {