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8329850: [AIX] Allow loading of different members of same shared library archive #18676

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8329850: [AIX] Allow loading of different members of same shared library archive #18676

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de6897e
JDK-8329850
JoKern65 Apr 8, 2024
3ec7964
change from hash to allocated string
JoKern65 Apr 25, 2024
b1ec5ed
cosmetic changes
JoKern65 Apr 25, 2024
584502a
Back to the roots
JoKern65 Apr 25, 2024
97ad367
set ptr to nullptr after free
JoKern65 Apr 25, 2024
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31 changes: 24 additions & 7 deletions src/hotspot/os/aix/porting_aix.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -906,10 +906,11 @@ struct TableLocker {
~TableLocker() { pthread_mutex_unlock(&g_handletable_mutex); }
};
struct handletableentry{
void* handle;
ino64_t inode;
dev64_t devid;
uint refcount;
void* handle;
ino64_t inode;
dev64_t devid;
char* member;
uint refcount;
};
constexpr unsigned init_num_handles = 128;
static unsigned max_handletable = 0;
Expand Down Expand Up @@ -1049,14 +1050,25 @@ void* Aix_dlopen(const char* filename, int Flags, const char** error_report) {
return nullptr;
}
else {
// extract member string if exist duplicate it and store pointer of it
// if member does not exist store nullptr
char* member = nullptr;
const char* substr;
if (filename[strlen(filename) - 1] == ')' && (substr = strrchr(filename, '('))) {
member = os::strdup(substr);
}
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@TheRealMDoerr TheRealMDoerr Apr 8, 2024

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Should work in practical cases, but what if a hash collision occurs?

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@JoKern65 JoKern65 Apr 8, 2024

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How likely is a hash collision? My first thought was to store the member string in an additional array. But there is no length limitation. So I cannot just add an char array of e.g. 20 chars, but have to use a pointer to an external dynamically loaded memory holding the string. I came to the conclusion that a hash is much more elegant with a neglectable small risk of a hash collision.

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@TheRealMDoerr TheRealMDoerr Apr 9, 2024

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I guess extremely unlikely. But if it happens, it will be an extremely annoying problem.
I'd probably use strdup, but let's hear what other reviewers think.


unsigned i = 0;
TableLocker lock;
// check if library belonging to filename is already loaded.
// If yes use stored handle from previous ::dlopen() and increase refcount
for (i = 0; i < g_handletable_used; i++) {
if ((p_handletable + i)->handle &&
(p_handletable + i)->inode == libstat.st_ino &&
(p_handletable + i)->devid == libstat.st_dev) {
(p_handletable + i)->devid == libstat.st_dev &&
(((p_handletable + i)->member == nullptr && member == nullptr) ||
((p_handletable + i)->member != nullptr && member != nullptr &&
strcmp((p_handletable + i)->member, member) == 0))) {
(p_handletable + i)->refcount++;
result = (p_handletable + i)->handle;
break;
Expand Down Expand Up @@ -1084,6 +1096,7 @@ void* Aix_dlopen(const char* filename, int Flags, const char** error_report) {
(p_handletable + i)->handle = result;
(p_handletable + i)->inode = libstat.st_ino;
(p_handletable + i)->devid = libstat.st_dev;
(p_handletable + i)->member = member;
(p_handletable + i)->refcount = 1;
}
else {
Expand Down Expand Up @@ -1131,7 +1144,7 @@ bool os::pd_dll_unload(void* libhandle, char* ebuf, int ebuflen) {
// while in the second case we simply have to nag.
res = (0 == ::dlclose(libhandle));
if (!res) {
// error analysis when dlopen fails
// error analysis when dlclose fails
const char* error_report = ::dlerror();
if (error_report == nullptr) {
error_report = "dlerror returned no error description";
Expand All @@ -1145,7 +1158,11 @@ bool os::pd_dll_unload(void* libhandle, char* ebuf, int ebuflen) {
if (i < g_handletable_used) {
if (res) {
// First case: libhandle was found (with refcount == 0) and ::dlclose successful,
// so delete entry from array
// so delete entry from array (do not forget to free member-string space if member exists)
if ((p_handletable + i)->member) {
os::free((p_handletable + i)->member);
(p_handletable + i)->member = nullptr;
}
g_handletable_used--;
// If the entry was the last one of the array, the previous g_handletable_used--
// is sufficient to remove the entry from the array, otherwise we move the last
Expand Down