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8320890: [AIX] Find a better way to mimic dl handle equality
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Reviewed-by: stuefe, mdoerr
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Joachim Kern authored and TheRealMDoerr committed Jan 11, 2024
1 parent e5aed6b commit b8ae4a8
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Showing 12 changed files with 338 additions and 114 deletions.
36 changes: 5 additions & 31 deletions src/hotspot/os/aix/os_aix.cpp
Expand Up @@ -1118,7 +1118,9 @@ void *os::dll_load(const char *filename, char *ebuf, int ebuflen) {
}

if (!filename || strlen(filename) == 0) {
::strncpy(ebuf, "dll_load: empty filename specified", ebuflen - 1);
if (ebuf != nullptr && ebuflen > 0) {
::strncpy(ebuf, "dll_load: empty filename specified", ebuflen - 1);
}
return nullptr;
}

Expand All @@ -1133,8 +1135,9 @@ void *os::dll_load(const char *filename, char *ebuf, int ebuflen) {
}

void* result;
const char* error_report = nullptr;
JFR_ONLY(NativeLibraryLoadEvent load_event(filename, &result);)
result = ::dlopen(filename, dflags);
result = Aix_dlopen(filename, dflags, &error_report);
if (result != nullptr) {
Events::log_dll_message(nullptr, "Loaded shared library %s", filename);
// Reload dll cache. Don't do this in signal handling.
Expand All @@ -1143,7 +1146,6 @@ void *os::dll_load(const char *filename, char *ebuf, int ebuflen) {
return result;
} else {
// error analysis when dlopen fails
const char* error_report = ::dlerror();
if (error_report == nullptr) {
error_report = "dlerror returned no error description";
}
Expand Down Expand Up @@ -3026,31 +3028,3 @@ void os::jfr_report_memory_info() {}

#endif // INCLUDE_JFR

// Simulate the library search algorithm of dlopen() (in os::dll_load)
int os::Aix::stat64x_via_LIBPATH(const char* path, struct stat64x* stat) {
if (path[0] == '/' ||
(path[0] == '.' && (path[1] == '/' ||
(path[1] == '.' && path[2] == '/')))) {
return stat64x(path, stat);
}

const char* env = getenv("LIBPATH");
if (env == nullptr || *env == 0)
return -1;

int ret = -1;
size_t libpathlen = strlen(env);
char* libpath = NEW_C_HEAP_ARRAY(char, libpathlen + 1, mtServiceability);
char* combined = NEW_C_HEAP_ARRAY(char, libpathlen + strlen(path) + 1, mtServiceability);
char *saveptr, *token;
strcpy(libpath, env);
for (token = strtok_r(libpath, ":", &saveptr); token != nullptr; token = strtok_r(nullptr, ":", &saveptr)) {
sprintf(combined, "%s/%s", token, path);
if (0 == (ret = stat64x(combined, stat)))
break;
}

FREE_C_HEAP_ARRAY(char*, combined);
FREE_C_HEAP_ARRAY(char*, libpath);
return ret;
}
2 changes: 0 additions & 2 deletions src/hotspot/os/aix/os_aix.hpp
Expand Up @@ -175,8 +175,6 @@ class os::Aix {
static bool platform_print_native_stack(outputStream* st, const void* context, char *buf, int buf_size, address& lastpc);
static void* resolve_function_descriptor(void* p);

// Simulate the library search algorithm of dlopen() (in os::dll_load)
static int stat64x_via_LIBPATH(const char* path, struct stat64x* stat);
};

#endif // OS_AIX_OS_AIX_HPP
278 changes: 278 additions & 0 deletions src/hotspot/os/aix/porting_aix.cpp
Expand Up @@ -21,6 +21,12 @@
* questions.
*
*/
// needs to be defined first, so that the implicit loaded xcoff.h header defines
// the right structures to analyze the loader header of 64 Bit executable files
// this is needed for rtv_linkedin_libpath() to get the linked (burned) in library
// search path of an XCOFF executable
#define __XCOFF64__
#include <xcoff.h>

#include "asm/assembler.hpp"
#include "compiler/disassembler.hpp"
Expand Down Expand Up @@ -891,3 +897,275 @@ bool AixMisc::query_stack_bounds_for_current_thread(stackbounds_t* out) {
return true;

}

// variables needed to emulate linux behavior in os::dll_load() if library is loaded twice
static pthread_mutex_t g_handletable_mutex = PTHREAD_MUTEX_INITIALIZER;

struct TableLocker {
TableLocker() { pthread_mutex_lock(&g_handletable_mutex); }
~TableLocker() { pthread_mutex_unlock(&g_handletable_mutex); }
};
struct handletableentry{
void* handle;
ino64_t inode;
dev64_t devid;
uint refcount;
};
constexpr unsigned init_num_handles = 128;
static unsigned max_handletable = 0;
static unsigned g_handletable_used = 0;
// We start with an empty array. At first use we will dynamically allocate memory for 128 entries.
// If this table is full we dynamically reallocate a memory reagion of double size, and so on.
static struct handletableentry* p_handletable = nullptr;

// get the library search path burned in to the executable file during linking
// If the libpath cannot be retrieved return an empty path
static const char* rtv_linkedin_libpath() {
constexpr int bufsize = 4096;
static char buffer[bufsize];
static const char* libpath = 0;

// we only try to retrieve the libpath once. After that try we
// let libpath point to buffer, which then contains a valid libpath
// or an empty string
if (libpath != nullptr) {
return libpath;
}

// retrieve the path to the currently running executable binary
// to open it
snprintf(buffer, 100, "/proc/%ld/object/a.out", (long)getpid());
FILE* f = nullptr;
struct xcoffhdr the_xcoff;
struct scnhdr the_scn;
struct ldhdr the_ldr;
constexpr size_t xcoffsz = FILHSZ + _AOUTHSZ_EXEC;
STATIC_ASSERT(sizeof(the_xcoff) == xcoffsz);
STATIC_ASSERT(sizeof(the_scn) == SCNHSZ);
STATIC_ASSERT(sizeof(the_ldr) == LDHDRSZ);
// read the generic XCOFF header and analyze the substructures
// to find the burned in libpath. In any case of error perform the assert
if (nullptr == (f = fopen(buffer, "r")) ||
xcoffsz != fread(&the_xcoff, 1, xcoffsz, f) ||
the_xcoff.filehdr.f_magic != U64_TOCMAGIC ||
0 != fseek(f, (FILHSZ + the_xcoff.filehdr.f_opthdr + (the_xcoff.aouthdr.o_snloader -1)*SCNHSZ), SEEK_SET) ||
SCNHSZ != fread(&the_scn, 1, SCNHSZ, f) ||
0 != strcmp(the_scn.s_name, ".loader") ||
0 != fseek(f, the_scn.s_scnptr, SEEK_SET) ||
LDHDRSZ != fread(&the_ldr, 1, LDHDRSZ, f) ||
0 != fseek(f, the_scn.s_scnptr + the_ldr.l_impoff, SEEK_SET) ||
0 == fread(buffer, 1, bufsize, f)) {
buffer[0] = 0;
assert(false, "could not retrieve burned in library path from executables loader section");
}

if (f) {
fclose(f);
}
libpath = buffer;

return libpath;
}

// Simulate the library search algorithm of dlopen() (in os::dll_load)
static bool search_file_in_LIBPATH(const char* path, struct stat64x* stat) {
if (path == nullptr)
return false;

char* path2 = os::strdup(path);
// if exist, strip off trailing (shr_64.o) or similar
char* substr;
if (path2[strlen(path2) - 1] == ')' && (substr = strrchr(path2, '('))) {
*substr = 0;
}

bool ret = false;
// If FilePath contains a slash character, FilePath is used directly,
// and no directories are searched.
// But if FilePath does not start with / or . we have to prepend it with ./
if (strchr(path2, '/')) {
stringStream combined;
if (*path2 == '/' || *path2 == '.') {
combined.print("%s", path2);
} else {
combined.print("./%s", path2);
}
ret = (0 == stat64x(combined.base(), stat));
os::free(path2);
return ret;
}

const char* env = getenv("LIBPATH");
if (env == nullptr) {
// no LIBPATH, try with LD_LIBRARY_PATH
env = getenv("LD_LIBRARY_PATH");
}

stringStream Libpath;
if (env == nullptr) {
// no LIBPATH or LD_LIBRARY_PATH given -> try only with burned in libpath
Libpath.print("%s", rtv_linkedin_libpath());
} else if (*env == 0) {
// LIBPATH or LD_LIBRARY_PATH given but empty -> try first with burned
// in libpath and with current working directory second
Libpath.print("%s:.", rtv_linkedin_libpath());
} else {
// LIBPATH or LD_LIBRARY_PATH given with content -> try first with
// LIBPATH or LD_LIBRARY_PATH and second with burned in libpath.
// No check against current working directory
Libpath.print("%s:%s", env, rtv_linkedin_libpath());
}

char* libpath = os::strdup(Libpath.base());

char *saveptr, *token;
for (token = strtok_r(libpath, ":", &saveptr); token != nullptr; token = strtok_r(nullptr, ":", &saveptr)) {
stringStream combined;
combined.print("%s/%s", token, path2);
if ((ret = (0 == stat64x(combined.base(), stat))))
break;
}

os::free(libpath);
os::free(path2);
return ret;
}

// specific AIX versions for ::dlopen() and ::dlclose(), which handles the struct g_handletable
// This way we mimic dl handle equality for a library
// opened a second time, as it is implemented on other platforms.
void* Aix_dlopen(const char* filename, int Flags, const char** error_report) {
assert(error_report != nullptr, "error_report is nullptr");
void* result;
struct stat64x libstat;

if (false == search_file_in_LIBPATH(filename, &libstat)) {
// file with filename does not exist
#ifdef ASSERT
result = ::dlopen(filename, Flags);
assert(result == nullptr, "dll_load: Could not stat() file %s, but dlopen() worked; Have to improve stat()", filename);
#endif
*error_report = "Could not load module .\nSystem error: No such file or directory";
return nullptr;
}
else {
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)->refcount++;
result = (p_handletable + i)->handle;
break;
}
}
if (i == g_handletable_used) {
// library not yet loaded. Check if there is space left in array
// to store new ::dlopen() handle
if (g_handletable_used == max_handletable) {
// No place in array anymore; increase array.
unsigned new_max = MAX2(max_handletable * 2, init_num_handles);
struct handletableentry* new_tab = (struct handletableentry*)::realloc(p_handletable, new_max * sizeof(struct handletableentry));
assert(new_tab != nullptr, "no more memory for handletable");
if (new_tab == nullptr) {
*error_report = "dlopen: no more memory for handletable";
return nullptr;
}
max_handletable = new_max;
p_handletable = new_tab;
}
// Library not yet loaded; load it, then store its handle in handle table
result = ::dlopen(filename, Flags);
if (result != nullptr) {
g_handletable_used++;
(p_handletable + i)->handle = result;
(p_handletable + i)->inode = libstat.st_ino;
(p_handletable + i)->devid = libstat.st_dev;
(p_handletable + i)->refcount = 1;
}
else {
// error analysis when dlopen fails
*error_report = ::dlerror();
if (*error_report == nullptr) {
*error_report = "dlerror returned no error description";
}
}
}
}
return result;
}

bool os::pd_dll_unload(void* libhandle, char* ebuf, int ebuflen) {
unsigned i = 0;
bool res = false;

if (ebuf && ebuflen > 0) {
ebuf[0] = '\0';
ebuf[ebuflen - 1] = '\0';
}

{
TableLocker lock;
// try to find handle in array, which means library was loaded by os::dll_load() call
for (i = 0; i < g_handletable_used; i++) {
if ((p_handletable + i)->handle == libhandle) {
// handle found, decrease refcount
assert((p_handletable + i)->refcount > 0, "Sanity");
(p_handletable + i)->refcount--;
if ((p_handletable + i)->refcount > 0) {
// if refcount is still >0 then we have to keep library and just return true
return true;
}
// refcount == 0, so we have to ::dlclose() the lib
// and delete the entry from the array.
break;
}
}

// If we reach this point either the libhandle was found with refcount == 0, or the libhandle
// was not found in the array at all. In both cases we have to ::dlclose the lib and perform
// the error handling. In the first case we then also have to delete the entry from the array
// while in the second case we simply have to nag.
res = (0 == ::dlclose(libhandle));
if (!res) {
// error analysis when dlopen fails
const char* error_report = ::dlerror();
if (error_report == nullptr) {
error_report = "dlerror returned no error description";
}
if (ebuf != nullptr && ebuflen > 0) {
snprintf(ebuf, ebuflen - 1, "%s", error_report);
}
assert(false, "os::pd_dll_unload() ::dlclose() failed");
}

if (i < g_handletable_used) {
if (res) {
// First case: libhandle was found (with refcount == 0) and ::dlclose successful,
// so delete entry from array
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
// entry of the array to the place of the entry we want to remove and overwrite it
if (i < g_handletable_used) {
*(p_handletable + i) = *(p_handletable + g_handletable_used);
(p_handletable + g_handletable_used)->handle = nullptr;
}
}
}
else {
// Second case: libhandle was not found (library was not loaded by os::dll_load())
// therefore nag
assert(false, "os::pd_dll_unload() library was not loaded by os::dll_load()");
}
}

// Update the dll cache
LoadedLibraries::reload();

return res;
} // end: os::pd_dll_unload()

2 changes: 2 additions & 0 deletions src/hotspot/os/aix/porting_aix.hpp
Expand Up @@ -115,4 +115,6 @@ class AixMisc {

};

void* Aix_dlopen(const char* filename, int Flags, const char** error_report);

#endif // OS_AIX_PORTING_AIX_HPP
22 changes: 22 additions & 0 deletions src/hotspot/os/bsd/os_bsd.cpp
Expand Up @@ -2530,3 +2530,25 @@ void os::jfr_report_memory_info() {
}

#endif // INCLUDE_JFR

bool os::pd_dll_unload(void* libhandle, char* ebuf, int ebuflen) {

if (ebuf && ebuflen > 0) {
ebuf[0] = '\0';
ebuf[ebuflen - 1] = '\0';
}

bool res = (0 == ::dlclose(libhandle));
if (!res) {
// error analysis when dlopen fails
const char* error_report = ::dlerror();
if (error_report == nullptr) {
error_report = "dlerror returned no error description";
}
if (ebuf != nullptr && ebuflen > 0) {
snprintf(ebuf, ebuflen - 1, "%s", error_report);
}
}

return res;
} // end: os::pd_dll_unload()

5 comments on commit b8ae4a8

@openjdk-notifier
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@JoKern65
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/backport jdk22u

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@openjdk openjdk bot commented on b8ae4a8 Feb 5, 2024

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@JoKern65 the backport was successfully created on the branch backport-JoKern65-b8ae4a8c in my personal fork of openjdk/jdk22u. To create a pull request with this backport targeting openjdk/jdk22u:master, just click the following link:

➡️ Create pull request

The title of the pull request is automatically filled in correctly and below you find a suggestion for the pull request body:

Hi all,

This pull request contains a backport of commit b8ae4a8c from the openjdk/jdk repository.

The commit being backported was authored by Joachim Kern on 11 Jan 2024 and was reviewed by Thomas Stuefe and Martin Doerr.

Thanks!

If you need to update the source branch of the pull then run the following commands in a local clone of your personal fork of openjdk/jdk22u:

$ git fetch https://github.com/openjdk-bots/jdk22u.git backport-JoKern65-b8ae4a8c:backport-JoKern65-b8ae4a8c
$ git checkout backport-JoKern65-b8ae4a8c
# make changes
$ git add paths/to/changed/files
$ git commit --message 'Describe additional changes made'
$ git push https://github.com/openjdk-bots/jdk22u.git backport-JoKern65-b8ae4a8c

⚠️ @JoKern65 You are not yet a collaborator in my fork openjdk-bots/jdk22u. An invite will be sent out and you need to accept it before you can proceed.

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/backport jdk21u-dev

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@openjdk openjdk bot commented on b8ae4a8 Feb 9, 2024

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@JoKern65 Could not automatically backport b8ae4a8c to openjdk/jdk21u-dev due to conflicts in the following files:

  • src/hotspot/os/aix/os_aix.cpp
  • src/hotspot/os/posix/os_posix.cpp

Please fetch the appropriate branch/commit and manually resolve these conflicts by using the following commands in your personal fork of openjdk/jdk21u-dev. Note: these commands are just some suggestions and you can use other equivalent commands you know.

# Fetch the up-to-date version of the target branch
$ git fetch --no-tags https://git.openjdk.org/jdk21u-dev.git master:master

# Check out the target branch and create your own branch to backport
$ git checkout master
$ git checkout -b backport-JoKern65-b8ae4a8c

# Fetch the commit you want to backport
$ git fetch --no-tags https://git.openjdk.org/jdk.git b8ae4a8c0985d1763ac48ba78943d8b992d7be77

# Backport the commit
$ git cherry-pick --no-commit b8ae4a8c0985d1763ac48ba78943d8b992d7be77
# Resolve conflicts now

# Commit the files you have modified
$ git add files/with/resolved/conflicts
$ git commit -m 'Backport b8ae4a8c0985d1763ac48ba78943d8b992d7be77'

Once you have resolved the conflicts as explained above continue with creating a pull request towards the openjdk/jdk21u-dev with the title Backport b8ae4a8c0985d1763ac48ba78943d8b992d7be77.

Below you can find a suggestion for the pull request body:

Hi all,

This pull request contains a backport of commit b8ae4a8c from the openjdk/jdk repository.

The commit being backported was authored by Joachim Kern on 11 Jan 2024 and was reviewed by Thomas Stuefe and Martin Doerr.

Thanks!

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