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[libunwind] Improve unwinder stack usage - II

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unwind_phase1 and unwind_phase2 allocate their own copies of unw_cursor_t buffers
on the stack. This can blow-up stack usage of the unwinder depending on how these
two functions get inlined into _Unwind_RaiseException. Clang seems to inline
unwind_phase1 into _Unwind_RaiseException but not unwind_phase2, thus creating
two unw_cursor_t buffers on the stack.

One way to work-around this problem is to mark both unwind_phase1 and
unwind_phase2 as noinline. This patch takes the less compiler-dependent approach
and explicitly allocate a unw_cursor_t buffer and pass that into unwind_phase1
and unwind_phase2 functions.

A follow-up patch will replicate this behavior for the non-EHABI and non-SJLJ
implementations.

Reviewers: jroelofs, bcraig.

Differential revision: http://reviews.llvm.org/D20320

llvm-svn: 271004
This commit is contained in:
Asiri Rathnayake 2016-05-27 15:41:45 +00:00
parent 4daf7f13b6
commit 45e59f7198
1 changed files with 24 additions and 24 deletions
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48
libunwind/src/Unwind-EHABI.cpp
View File

@ -438,15 +438,14 @@ extern "C" _Unwind_Reason_Code __aeabi_unwind_cpp_pr2(
}
static _Unwind_Reason_Code
unwind_phase1(unw_context_t *uc, _Unwind_Exception *exception_object) {
unwind_phase1(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *exception_object) {
// EHABI #7.3 discusses preserving the VRS in a "temporary VRS" during
// phase 1 and then restoring it to the "primary VRS" for phase 2. The
// effect is phase 2 doesn't see any of the VRS manipulations from phase 1.
// In this implementation, the phases don't share the VRS backing store.
// Instead, they are passed the original |uc| and they create a new VRS
// from scratch thus achieving the same effect.
unw_cursor_t cursor1;
unw_init_local(&cursor1, uc);
unw_init_local(cursor, uc);
// Walk each frame looking for a place to stop.
for (bool handlerNotFound = true; handlerNotFound;) {
@ -454,7 +453,7 @@ unwind_phase1(unw_context_t *uc, _Unwind_Exception *exception_object) {
#if !_LIBUNWIND_ARM_EHABI
// Ask libuwind to get next frame (skip over first which is
// _Unwind_RaiseException).
int stepResult = unw_step(&cursor1);
int stepResult = unw_step(cursor);
if (stepResult == 0) {
_LIBUNWIND_TRACE_UNWINDING("unwind_phase1(ex_ojb=%p): unw_step() reached "
"bottom => _URC_END_OF_STACK\n",
@ -470,7 +469,7 @@ unwind_phase1(unw_context_t *uc, _Unwind_Exception *exception_object) {
// See if frame has code to run (has personality routine).
unw_proc_info_t frameInfo;
if (unw_get_proc_info(&cursor1, &frameInfo) != UNW_ESUCCESS) {
if (unw_get_proc_info(cursor, &frameInfo) != UNW_ESUCCESS) {
_LIBUNWIND_TRACE_UNWINDING("unwind_phase1(ex_ojb=%p): unw_get_proc_info "
"failed => _URC_FATAL_PHASE1_ERROR\n",
static_cast<void *>(exception_object));
@ -482,12 +481,12 @@ unwind_phase1(unw_context_t *uc, _Unwind_Exception *exception_object) {
char functionBuf[512];
const char *functionName = functionBuf;
unw_word_t offset;
if ((unw_get_proc_name(&cursor1, functionBuf, sizeof(functionBuf),
if ((unw_get_proc_name(cursor, functionBuf, sizeof(functionBuf),
&offset) != UNW_ESUCCESS) ||
(frameInfo.start_ip + offset > frameInfo.end_ip))
functionName = ".anonymous.";
unw_word_t pc;
unw_get_reg(&cursor1, UNW_REG_IP, &pc);
unw_get_reg(cursor, UNW_REG_IP, &pc);
_LIBUNWIND_TRACE_UNWINDING(
"unwind_phase1(ex_ojb=%p): pc=0x%llX, start_ip=0x%llX, func=%s, "
"lsda=0x%llX, personality=0x%llX\n",
@ -505,7 +504,7 @@ unwind_phase1(unw_context_t *uc, _Unwind_Exception *exception_object) {
"unwind_phase1(ex_ojb=%p): calling personality function %p\n",
static_cast<void *>(exception_object),
reinterpret_cast<void *>(reinterpret_cast<uintptr_t>(p)));
struct _Unwind_Context *context = (struct _Unwind_Context *)(&cursor1);
struct _Unwind_Context *context = (struct _Unwind_Context *)(cursor);
exception_object->pr_cache.fnstart = frameInfo.start_ip;
exception_object->pr_cache.ehtp =
(_Unwind_EHT_Header *)frameInfo.unwind_info;
@ -553,12 +552,11 @@ unwind_phase1(unw_context_t *uc, _Unwind_Exception *exception_object) {
return _URC_NO_REASON;
}
static _Unwind_Reason_Code unwind_phase2(unw_context_t *uc,
static _Unwind_Reason_Code unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor,
_Unwind_Exception *exception_object,
bool resume) {
// See comment at the start of unwind_phase1 regarding VRS integrity.
unw_cursor_t cursor2;
unw_init_local(&cursor2, uc);
unw_init_local(cursor, uc);
_LIBUNWIND_TRACE_UNWINDING("unwind_phase2(ex_ojb=%p)\n",
static_cast<void *>(exception_object));
@ -580,13 +578,13 @@ static _Unwind_Reason_Code unwind_phase2(unw_context_t *uc,
// for. After this, continue unwinding as if normal.
//
// See #7.4.6 for details.
unw_set_reg(&cursor2, UNW_REG_IP,
unw_set_reg(cursor, UNW_REG_IP,
exception_object->unwinder_cache.reserved2);
resume = false;
}
#if !_LIBUNWIND_ARM_EHABI
int stepResult = unw_step(&cursor2);
int stepResult = unw_step(cursor);
if (stepResult == 0) {
_LIBUNWIND_TRACE_UNWINDING("unwind_phase2(ex_ojb=%p): unw_step() reached "
"bottom => _URC_END_OF_STACK\n",
@ -603,8 +601,8 @@ static _Unwind_Reason_Code unwind_phase2(unw_context_t *uc,
// Get info about this frame.
unw_word_t sp;
unw_proc_info_t frameInfo;
unw_get_reg(&cursor2, UNW_REG_SP, &sp);
if (unw_get_proc_info(&cursor2, &frameInfo) != UNW_ESUCCESS) {
unw_get_reg(cursor, UNW_REG_SP, &sp);
if (unw_get_proc_info(cursor, &frameInfo) != UNW_ESUCCESS) {
_LIBUNWIND_TRACE_UNWINDING("unwind_phase2(ex_ojb=%p): unw_get_proc_info "
"failed => _URC_FATAL_PHASE1_ERROR\n",
static_cast<void *>(exception_object));
@ -616,7 +614,7 @@ static _Unwind_Reason_Code unwind_phase2(unw_context_t *uc,
char functionBuf[512];
const char *functionName = functionBuf;
unw_word_t offset;
if ((unw_get_proc_name(&cursor2, functionBuf, sizeof(functionBuf),
if ((unw_get_proc_name(cursor, functionBuf, sizeof(functionBuf),
&offset) != UNW_ESUCCESS) ||
(frameInfo.start_ip + offset > frameInfo.end_ip))
functionName = ".anonymous.";
@ -632,7 +630,7 @@ static _Unwind_Reason_Code unwind_phase2(unw_context_t *uc,
if (frameInfo.handler != 0) {
__personality_routine p =
(__personality_routine)(long)(frameInfo.handler);
struct _Unwind_Context *context = (struct _Unwind_Context *)(&cursor2);
struct _Unwind_Context *context = (struct _Unwind_Context *)(cursor);
// EHABI #7.2
exception_object->pr_cache.fnstart = frameInfo.start_ip;
exception_object->pr_cache.ehtp =
@ -661,8 +659,8 @@ static _Unwind_Reason_Code unwind_phase2(unw_context_t *uc,
// We may get control back if landing pad calls _Unwind_Resume().
if (_LIBUNWIND_TRACING_UNWINDING) {
unw_word_t pc;
unw_get_reg(&cursor2, UNW_REG_IP, &pc);
unw_get_reg(&cursor2, UNW_REG_SP, &sp);
unw_get_reg(cursor, UNW_REG_IP, &pc);
unw_get_reg(cursor, UNW_REG_SP, &sp);
_LIBUNWIND_TRACE_UNWINDING("unwind_phase2(ex_ojb=%p): re-entering "
"user code with ip=0x%llX, sp=0x%llX\n",
static_cast<void *>(exception_object),
@ -673,10 +671,10 @@ static _Unwind_Reason_Code unwind_phase2(unw_context_t *uc,
// EHABI #7.4.1 says we need to preserve pc for when _Unwind_Resume
// is called back, to find this same frame.
unw_word_t pc;
unw_get_reg(&cursor2, UNW_REG_IP, &pc);
unw_get_reg(cursor, UNW_REG_IP, &pc);
exception_object->unwinder_cache.reserved2 = (uint32_t)pc;
}
unw_resume(&cursor2);
unw_resume(cursor);
// unw_resume() only returns if there was an error.
return _URC_FATAL_PHASE2_ERROR;
@ -705,6 +703,7 @@ _Unwind_RaiseException(_Unwind_Exception *exception_object) {
_LIBUNWIND_TRACE_API("_Unwind_RaiseException(ex_obj=%p)\n",
static_cast<void *>(exception_object));
unw_context_t uc;
unw_cursor_t cursor;
unw_getcontext(&uc);
// This field for is for compatibility with GCC to say this isn't a forced
@ -712,12 +711,12 @@ _Unwind_RaiseException(_Unwind_Exception *exception_object) {
exception_object->unwinder_cache.reserved1 = 0;
// phase 1: the search phase
_Unwind_Reason_Code phase1 = unwind_phase1(&uc, exception_object);
_Unwind_Reason_Code phase1 = unwind_phase1(&uc, &cursor, exception_object);
if (phase1 != _URC_NO_REASON)
return phase1;
// phase 2: the clean up phase
return unwind_phase2(&uc, exception_object, false);
return unwind_phase2(&uc, &cursor, exception_object, false);
}
_LIBUNWIND_EXPORT void _Unwind_Complete(_Unwind_Exception* exception_object) {
@ -742,12 +741,13 @@ _Unwind_Resume(_Unwind_Exception *exception_object) {
_LIBUNWIND_TRACE_API("_Unwind_Resume(ex_obj=%p)\n",
static_cast<void *>(exception_object));
unw_context_t uc;
unw_cursor_t cursor;
unw_getcontext(&uc);
// _Unwind_RaiseException on EHABI will always set the reserved1 field to 0,
// which is in the same position as private_1 below.
// TODO(ajwong): Who wronte the above? Why is it true?
unwind_phase2(&uc, exception_object, true);
unwind_phase2(&uc, &cursor, exception_object, true);
// Clients assume _Unwind_Resume() does not return, so all we can do is abort.
_LIBUNWIND_ABORT("_Unwind_Resume() can't return");