commit 7cdd140cbccc8eb62a20d12a03bed83765cbc066 Author: Stefan Liebler Date: Fri Jul 31 13:42:52 2015 +0200 S390: Fix "backtrace() returns infinitely deep stack frames with makecontext()" [BZ #18508]. On s390/s390x backtrace(buffer, size) returns the series of called functions until "makecontext_ret" and additional entries (up to "size") with "makecontext_ret". GDB-backtrace is also warning: "Backtrace stopped: previous frame identical to this frame (corrupt stack?)" To reproduce this scenario you have to setup a new context with makecontext() and activate it with setcontext(). See e.g. cf() function in testcase stdlib/tst-makecontext.c. Or see bug in libgo "Bug 66303 - runtime.Caller() returns infinitely deep stack frames on s390x " (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66303). This patch omits the cfi_startproc/cfi_endproc directives in ENTRY/END macro of __makecontext_ret. Thus no frame information is generated in .eh_frame and backtrace stops after __makecontext_ret. There is also no .eh_frame info for _start or thread_start functions. ChangeLog: [BZ #18508] * stdlib/Makefile ($(objpfx)tst-makecontext3): Depend on $(libdl). * stdlib/tst-makecontext.c (cf): Test if _Unwind_Backtrace is not called infinitely times. (backtrace_helper): New function. (trace_arg): New struct. (st1): Enlarge stack size. * sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S: (__makecontext_ret): Omit cfi_startproc and cfi_endproc. * sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S: Likewise. diff --git a/stdlib/Makefile b/stdlib/Makefile index 8f22c8d..c1e80d7 100644 --- a/stdlib/Makefile +++ b/stdlib/Makefile @@ -154,3 +154,4 @@ $(objpfx)bug-getcontext: $(link-libm) $(objpfx)tst-strtod-round: $(link-libm) $(objpfx)tst-tininess: $(link-libm) $(objpfx)tst-strtod-underflow: $(link-libm) +$(objpfx)tst-makecontext: $(libdl) diff --git a/stdlib/tst-makecontext.c b/stdlib/tst-makecontext.c index eb6e89b..1420857 100644 --- a/stdlib/tst-makecontext.c +++ b/stdlib/tst-makecontext.c @@ -19,23 +19,62 @@ #include #include #include +#include +#include +#include +#include ucontext_t ucp; -char st1[8192]; +char st1[16384]; __thread int thr; int somevar = -76; long othervar = -78L; +struct trace_arg +{ + int cnt, size; +}; + +static _Unwind_Reason_Code +backtrace_helper (struct _Unwind_Context *ctx, void *a) +{ + struct trace_arg *arg = a; + if (++arg->cnt == arg->size) + return _URC_END_OF_STACK; + return _URC_NO_REASON; +} + void cf (int i) { + struct trace_arg arg = { .size = 100, .cnt = -1 }; + void *handle; + _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *); + if (i != othervar || thr != 94) { printf ("i %d thr %d\n", i, thr); exit (1); } + /* Test if callback function of _Unwind_Backtrace is not called infinitely + times. See Bug 18508 or gcc bug "Bug 66303 - runtime.Caller() returns + infinitely deep stack frames on s390x.". + The go runtime calls backtrace_full() in + /libbacktrace/backtrace.c, which uses _Unwind_Backtrace(). */ + handle = dlopen (LIBGCC_S_SO, RTLD_LAZY); + if (handle != NULL) + { + unwind_backtrace = dlsym (handle, "_Unwind_Backtrace"); + if (unwind_backtrace != NULL) + { + unwind_backtrace (backtrace_helper, &arg); + assert (arg.cnt != -1 && arg.cnt < 100); + } + dlclose (handle); + } + /* Since uc_link below has been set to NULL, setcontext is supposed to terminate the process normally after this function returns. */ } diff --git a/sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S b/sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S index ab172bb..365c2b0 100644 --- a/sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S +++ b/sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S @@ -17,6 +17,14 @@ #include +/* We do not want .eh_frame info so that __makecontext_ret stops unwinding + if backtrace was called within a context created by makecontext. (There + is also no .eh_frame info for _start or thread_start.) */ +#undef cfi_startproc +#define cfi_startproc +#undef cfi_endproc +#define cfi_endproc + ENTRY(__makecontext_ret) basr %r14,%r7 ltr %r8,%r8 /* Check whether uc_link is 0. */ diff --git a/sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S b/sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S index cbd88e1..c4a43bd 100644 --- a/sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S +++ b/sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S @@ -17,6 +17,14 @@ #include +/* We do not want .eh_frame info so that __makecontext_ret stops unwinding + if backtrace was called within a context created by makecontext. (There + is also no .eh_frame info for _start or thread_start.) */ +#undef cfi_startproc +#define cfi_startproc +#undef cfi_endproc +#define cfi_endproc + ENTRY(__makecontext_ret) basr %r14,%r7 ltgr %r8,%r8 /* Check whether uc_link is 0. */