From 490b84a72c8eecf03e8befbdcf973e468f2d310c Mon Sep 17 00:00:00 2001 From: Anton Kolesov Date: Wed, 28 Jun 2017 20:04:33 +0300 Subject: arc: Ensure that debugger can recognize sigrestorer An issue has been found with current implementation of signal restorer function in uClibc and how GDB handles it. When debugger information is not present, everything worked fine, because GDB would use a built-in logic to determine if function is a signal restorer. However when debugging information is present, debugger would rely solely on it and wouldn't use ARC-specific functions to detect signal handler frames. Because debug information for signal restorer is generated completely by the compiler, it lacks a marker, that identifies this as a signal frame that requires special handling. While it is possible to insert that marker via inline assembly, that still doesn't solve the whole problem, because some other expectations are not met by the debug information - there is no "nop" in front of the function, needed to fool debugger into thinking that this was a function call, and references to previous frame information need to be described manually. The simplest way to fix the problem is just to make sure that signal restorer function will not have any debug function at all, which can be done by writing it in assembly. Alternative, more complex, solution, where debug information for signal frame is manually defined can be found in glibc/sysdeps/unix/sysv/linux/x86_64/sigaction.c [1]. [1] https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/x86_64/sigaction.c;hb=HEAD Signed-off-by: Anton Kolesov --- libc/sysdeps/linux/arc/Makefile.arch | 3 ++- libc/sysdeps/linux/arc/sigaction.c | 6 +----- libc/sysdeps/linux/arc/sigrestorer.S | 25 +++++++++++++++++++++++++ 3 files changed, 28 insertions(+), 6 deletions(-) create mode 100644 libc/sysdeps/linux/arc/sigrestorer.S diff --git a/libc/sysdeps/linux/arc/Makefile.arch b/libc/sysdeps/linux/arc/Makefile.arch index 1a52fc9bf..a4aa72c0a 100644 --- a/libc/sysdeps/linux/arc/Makefile.arch +++ b/libc/sysdeps/linux/arc/Makefile.arch @@ -7,4 +7,5 @@ CSRC-y := syscall.c sigaction.c __syscall_error.c cacheflush.c -SSRC-y := __longjmp.S setjmp.S bsd-setjmp.S bsd-_setjmp.S vfork.S clone.S +SSRC-y := __longjmp.S setjmp.S bsd-setjmp.S bsd-_setjmp.S vfork.S clone.S \ + sigrestorer.S diff --git a/libc/sysdeps/linux/arc/sigaction.c b/libc/sysdeps/linux/arc/sigaction.c index 67ca38aca..64a6255c4 100644 --- a/libc/sysdeps/linux/arc/sigaction.c +++ b/libc/sysdeps/linux/arc/sigaction.c @@ -13,11 +13,7 @@ /* * Default sigretrun stub if user doesn't specify SA_RESTORER */ -static void attribute_optimize("Os") __attribute_noinline__ -__default_rt_sa_restorer(void) -{ - INTERNAL_SYSCALL_NCS(__NR_rt_sigreturn, , 0); -} +extern void __default_rt_sa_restorer(void); #define SA_RESTORER 0x04000000 diff --git a/libc/sysdeps/linux/arc/sigrestorer.S b/libc/sysdeps/linux/arc/sigrestorer.S new file mode 100644 index 000000000..e4deb6bd4 --- /dev/null +++ b/libc/sysdeps/linux/arc/sigrestorer.S @@ -0,0 +1,25 @@ +/* + * Copyright (C) 2017 Synopsys, Inc. (www.synopsys.com) + * + * Licensed under the LGPL v2.1 or later, see the file COPYING.LIB in this tarball. + */ + +#include + +/* + * Default sigretrun stub if user doesn't specify SA_RESTORER. + */ + +.section .text +.align 4 +.global __default_rt_sa_restorer +.type __default_rt_sa_restorer, @function + +; This "nop" is needed here, because debugger would assume that this function +; called the signal handler, therefore it cannot start on the "mov" +; instruction, at which execution will jump to. + nop +__default_rt_sa_restorer: + mov r8, __NR_rt_sigreturn + ARC_TRAP_INSN + -- cgit v1.2.3