Commit 9738e8b6 authored by Ben Gamari's avatar Ben Gamari Committed by Ben Gamari

Use SIGQUIT for DWARF backtraces instead of SIGUSR2

Reviewers: austin, erikd, simonmar

Subscribers: NicolasT, rwbarton, thomie

Differential Revision:
parent d11611f5
......@@ -157,6 +157,12 @@ Runtime system
- The GHCi runtime linker on Windows now supports the `big-obj` file format.
- The runtime system's :ref:`native stack backtrace <backtrace-signal>` support
on POSIX platforms is now triggered by ``SIGQUIT`` instead of ``SIGUSR2`` as
it was in previous releases. This change is to bring GHC's behavior into
compliance with the model set by the most Java virtual machine
Template Haskell
......@@ -185,16 +185,21 @@ Stack trace functionality is exposed for use by Haskell programs in the
:base-ref:`GHC.ExecutionStack.` module. See the Haddock
documentation in this module for details regarding usage.
Requesting a stack trace with ``SIGUSR2``
.. _backtrace_signal:
Requesting a stack trace with ``SIGQUIT``
On POSIX-compatible platforms GHC's runtime system (when built with ``libdw``
support) will produce a stack trace on ``stderr`` when a ``SIGUSR2`` signal is
received. For instance (using the same ``fib.hs`` as above),
support) will produce a stack trace on ``stderr`` when a ``SIGQUIT`` signal is
received (on many systems this signal can be sent using :kbd:`Ctrl-\\`). For
instance (using the same ``fib.hs`` as above),
.. code-block:: sh
$ ./fib & killall -SIGUSR2 fib
$ ./fib & killall -SIGQUIT fib
Caught SIGQUIT; Backtrace:
0x7f3176b15dd8 dwfl_thread_getframes (/usr/lib/x86_64-linux-gnu/
0x7f3176b1582f (null) (/usr/lib/x86_64-linux-gnu/
0x7f3176b15b57 dwfl_getthreads (/usr/lib/x86_64-linux-gnu/
......@@ -528,10 +528,10 @@ shutdown_handler(int sig STG_UNUSED)
/* -----------------------------------------------------------------------------
* SIGUSR2 handler.
* SIGQUIT handler.
* We try to give the user an indication of what we are currently doing
* in response to SIGUSR2.
* in response to SIGQUIT.
* -------------------------------------------------------------------------- */
static void
backtrace_handler(int sig STG_UNUSED)
......@@ -539,7 +539,7 @@ backtrace_handler(int sig STG_UNUSED)
LibdwSession *session = libdwInit();
Backtrace *bt = libdwGetBacktrace(session);
fprintf(stderr, "\nCaught SIGUSR2; Backtrace:\n");
fprintf(stderr, "\nCaught SIGQUIT; Backtrace:\n");
libdwPrintBacktrace(session, stderr, bt);
......@@ -721,12 +721,12 @@ initDefaultHandlers(void)
sysErrorBelch("warning: failed to install SIGPIPE handler");
// Print a backtrace on SIGUSR2
// Print a backtrace on SIGQUIT
action.sa_handler = backtrace_handler;
action.sa_flags = 0;
if (sigaction(SIGUSR2, &action, &oact) != 0) {
sysErrorBelch("warning: failed to install SIGUSR2 handler");
if (sigaction(SIGQUIT, &action, &oact) != 0) {
sysErrorBelch("warning: failed to install SIGQUIT handler");
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