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Bug 886736 - Disable on-demand decompression when latency to get into segfault handlers is too high. r=nfroyd

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This commit is contained in:
Mike Hommey 2013-10-01 15:30:45 +09:00
parent e88d48b47d
commit f6addb05b1
2 changed files with 49 additions and 5 deletions
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53
mozglue/linker/ElfLoader.cpp
View File

@ -14,6 +14,7 @@
#include "CustomElf.h"
#include "Mappable.h"
#include "Logging.h"
#include <inttypes.h>
#if defined(ANDROID)
#include <sys/syscall.h>
@ -908,8 +909,34 @@ Divert(T func, T new_func)
}
#endif
namespace {
/* Clock that only accounts for time spent in the current process. */
static uint64_t ProcessTimeStamp_Now()
{
struct timespec ts;
int rv = clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts);
if (rv != 0) {
return 0;
}
uint64_t baseNs = (uint64_t)ts.tv_sec * 1000000000;
return baseNs + (uint64_t)ts.tv_nsec;
}
}
/* Data structure used to pass data to the temporary signal handler,
* as well as triggering a test crash. */
struct TmpData {
volatile int crash_int;
volatile uint64_t crash_timestamp;
};
SEGVHandler::SEGVHandler()
: registeredHandler(false), signalHandlingBroken(false)
, signalHandlingSlow(false)
{
/* Initialize oldStack.ss_flags to an invalid value when used to set
* an alternative stack, meaning we haven't got information about the
@ -925,7 +952,11 @@ SEGVHandler::SEGVHandler()
* making it impossible for on-demand decompression to work. To check if
* we're on such a device, setup a temporary handler and deliberately
* trigger a segfault. The handler will set signalHandlingBroken if the
* provided information is bogus. */
* provided information is bogus.
* Some other devices have a kernel option enabled that makes SIGSEGV handler
* have an overhead so high that it affects how on-demand decompression
* performs. The handler will also set signalHandlingSlow if the triggered
* SIGSEGV took too much time. */
struct sigaction action;
action.sa_sigaction = &SEGVHandler::test_handler;
sigemptyset(&action.sa_mask);
@ -933,14 +964,17 @@ SEGVHandler::SEGVHandler()
action.sa_restorer = NULL;
if (sys_sigaction(SIGSEGV, &action, NULL))
return;
stackPtr.Assign(MemoryRange::mmap(NULL, PageSize(), PROT_NONE,
stackPtr.Assign(MemoryRange::mmap(NULL, PageSize(), PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0));
if (stackPtr.get() == MAP_FAILED)
return;
*((volatile int*)stackPtr.get()) = 123;
TmpData *data = reinterpret_cast<TmpData*>(stackPtr.get());
data->crash_timestamp = ProcessTimeStamp_Now();
mprotect(stackPtr, stackPtr.GetLength(), PROT_NONE);
data->crash_int = 123;
stackPtr.Assign(MAP_FAILED, 0);
if (signalHandlingBroken) {
if (signalHandlingBroken || signalHandlingSlow) {
/* Restore the original segfault signal handler. */
sys_sigaction(SIGSEGV, &this->action, NULL);
return;
@ -983,13 +1017,22 @@ SEGVHandler::~SEGVHandler()
/* Test handler for a deliberately triggered SIGSEGV that determines whether
* useful information is provided to signal handlers, particularly whether
* si_addr is filled in properly. */
* si_addr is filled in properly, and whether the segfault handler is called
* quickly enough. */
void SEGVHandler::test_handler(int signum, siginfo_t *info, void *context)
{
SEGVHandler &that = ElfLoader::Singleton;
if (signum != SIGSEGV || info == NULL || info->si_addr != that.stackPtr.get())
that.signalHandlingBroken = true;
mprotect(that.stackPtr, that.stackPtr.GetLength(), PROT_READ | PROT_WRITE);
TmpData *data = reinterpret_cast<TmpData*>(that.stackPtr.get());
uint64_t latency = ProcessTimeStamp_Now() - data->crash_timestamp;
DEBUG_LOG("SEGVHandler latency: %" PRIu64, latency);
/* See bug 886736 for timings on different devices, 150 µs is reasonably above
* the latency on "working" devices and seems to be reasonably fast to incur
* a huge overhead to on-demand decompression. */
if (latency > 150000)
that.signalHandlingSlow = true;
}
/* TODO: "properly" handle signal masks and flags */

1
mozglue/linker/ElfLoader.h
View File

@ -344,6 +344,7 @@ private:
bool registeredHandler;
bool signalHandlingBroken;
bool signalHandlingSlow;
};
/**