libc: implement sigsetjmp(), siglongjmp()

This patch implements the sigsetjmp()/siglongjmp() functions. Fixes #241.

sigsetjmp() and siglongjmp() are similar to setjmp() and longjmp(), except
that they also save and restore the signals mask. Signals are hardly useful
in OSv, so we don't necessarily need this signal mask feature, but we still
want to implement these functions, if only so that applications which use
them by default could run (see issue #241).

Most of the code in this patch is from Musl 1.0.0, with a few small
modifications - namely, call our sigprocmask() function instead a Linux
syscall. Note I copied the x64 version of sigsetjmp.s only. Musl also
has this file for ARM and other architectures. Interestingly we already
had in our source tree, but didn't use, block.c, and this patch starts
to use it.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

include/api/setjmp.h

@@ -9,27 +9,26 @@ extern "C" {
 
 #include <bits/setjmp.h>
 
+typedef struct __jmp_buf_tag {
+	__jmp_buf __jb;
+	unsigned long __fl;
+	unsigned long __ss[128/sizeof(long)];
+} jmp_buf[1];
 
 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
  || defined(_BSD_SOURCE)
-typedef struct __sigjmp_buf {
-	jmp_buf __jb;
-	unsigned long __fl;
-	unsigned long __ss[128/sizeof(long)];
-} sigjmp_buf[1];
+typedef jmp_buf sigjmp_buf;
 int sigsetjmp (sigjmp_buf, int);
 _Noreturn void siglongjmp (sigjmp_buf, int);
 #endif
 
-
 #if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
  || defined(_BSD_SOURCE)
 int _setjmp (jmp_buf);
 _Noreturn void _longjmp (jmp_buf, int);
 #endif
 
-
 int setjmp (jmp_buf);
 _Noreturn void longjmp (jmp_buf, int);
 

include/api/x64/bits/setjmp.h

-typedef unsigned long jmp_buf[8];
+typedef unsigned long __jmp_buf[8];

libc/build.mk

@@ -385,6 +385,9 @@ libc += arch/$(arch)/setjmp/longjmp.o
 
 libc += signal/sigrtmax.o
 libc += signal/sigrtmin.o
+libc += signal/siglongjmp.o
+libc += signal/sigsetjmp.o
+libc += signal/block.o
 
 libc += stdio/__fclose_ca.o
 libc += stdio/__fdopen.o

libc/signal/block.c

-#include "pthread_impl.h"
 #include "syscall.h"
 #include <signal.h>
 
@@ -30,15 +29,15 @@ static const unsigned long app_mask[] = {
 
 void __block_all_sigs(void *set)
 {
-	__syscall(SYS_rt_sigprocmask, SIG_BLOCK, &all_mask, set, _NSIG/8);
+	sigprocmask(SIG_BLOCK, (void*)&all_mask, set);
 }
 
 void __block_app_sigs(void *set)
 {
-	__syscall(SYS_rt_sigprocmask, SIG_BLOCK, &app_mask, set, _NSIG/8);
+	sigprocmask(SIG_BLOCK, (void*)&app_mask, set);
 }
 
 void __restore_sigs(void *set)
 {
-	__syscall(SYS_rt_sigprocmask, SIG_SETMASK, set, 0, _NSIG/8);
+	sigprocmask(SIG_SETMASK, set, 0);
 }

libc/signal/siglongjmp.c

+#include <setjmp.h>
+
+extern void __restore_sigs(void *set);
+
+_Noreturn void siglongjmp(sigjmp_buf buf, int ret)
+{
+	if (buf->__fl) __restore_sigs(buf->__ss);
+	longjmp(buf, ret);
+}

libc/signal/sigsetjmp.s

+/* Copyright 2011-2012 Nicholas J. Kain, licensed under standard MIT license */
+.global sigsetjmp
+.type sigsetjmp,@function
+sigsetjmp:
+	andl %esi,%esi
+	movq %rsi,64(%rdi)
+	jz 1f
+	pushq %rdi
+	leaq 72(%rdi),%rdx
+	xorl %esi,%esi
+	movl $2,%edi
+	call sigprocmask
+	popq %rdi
+1:	jmp setjmp