| Summary: | ltrace doesn't support re-entrant library calls on ppc64 | ||
|---|---|---|---|
| Product: | Red Hat Enterprise Linux 6 | Reporter: | Petr Machata <pmachata> |
| Component: | ltrace | Assignee: | Petr Machata <pmachata> |
| Status: | CLOSED WONTFIX | QA Contact: | qe-baseos-tools-bugs |
| Severity: | unspecified | Docs Contact: | |
| Priority: | unspecified | ||
| Version: | 6.6 | CC: | law, mcermak, mnewsome, ohudlick |
| Target Milestone: | rc | ||
| Target Release: | --- | ||
| Hardware: | Unspecified | ||
| OS: | Unspecified | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | Bug Fix | |
| Doc Text: | Story Points: | --- | |
| Clone Of: | Environment: | ||
| Last Closed: | 2014-06-18 18:26:07 UTC | Type: | --- |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
|
Description
Petr Machata
2011-11-11 12:13:37 UTC
I'm pasting the relevant contents of the linked bug, as the bug itself is not publicly available:
#ifdef LIB
void call(void (*what) ()) {
if (what)
what();
}
#else
void call(void (*) ());
void ble() {
call(0);
}
int main(int argc, char *argv[]) {
call(&ble);
return 0;
}
#endif
On ppc64:
# gcc -DLIB -m64 rec.c -fPIC -shared -o rec.so
# gcc -ULIB -m64 rec.c rec.so -Wl,-rpath,. -o rec
# ./ltrace ./rec
_start(1, 0xfffff9ff2c8, 0xfffff9ff2d8, <unfinished ...>
__libc_start_main(1, 0xfffff9ff2c8, 0xfffff9ff2d8, <unfinished ...>
call(0x10010be8, 0xfffff9ff2c8, 0xfffff9ff2d8) = 0
+++ exited (status 0) +++
On ppc32:
# gcc -DLIB rec.c -fPIC -shared -o rec.so
# gcc -ULIB rec.c rec.so -Wl,-rpath,. -o rec
# ./ltrace ./rec
_start(1, 0xffe5f3f4, 0xffe5f3fc, <unfinished ...>
__libc_start_main(1, 0xffe5f3f4, 0xffe5f3fc, <unfinished ...>
call(0x100015bc, 0xffe5f3f4, 0xffe5f3fc, <unfinished ...>
call(0, 0xffe5f3f4, 0xffe5f3fc) = 0
<... call resumed> ) = 0
+++ exited (status 0) +++
The deal is that on ppc, the PLT entry is changed after the first call. So ltrace knows it has to re-insert the breakpoint. But it cannot do so right away, when the PLT breakpoint is hit, it has to wait for the dynamic linker to actually change the entry first. So it does the re-insertion on _return_ from the function. Which is clever, except in case of re-entrant functions (or in multi-threaded app) this means that we miss all further calls to this one function until the first invocation returns.
The simple way out, viz. keeping everyone blocked until the first thread returns, is a no-go. Apart from it being rather horrible, some functions don't actually return (__libc_start_main comes to mind).
This Bugzilla has been reviewed by Red Hat and is not planned on being addressed in Red Hat Enterprise Linux 5, and therefore will be moved to Red Hat Enterprise Linux 6. If this bug is critical to production systems, please contact your Red Hat support representative and provide sufficient business justification. Development Management has reviewed and declined this request. You may appeal this decision by reopening this request. *** Bug 1210725 has been marked as a duplicate of this bug. *** |