Add comment explaining that changing the __restore and __restore_rt

signal return code will break GDB.

diff --git a/sysdeps/unix/sysv/linux/i386/sigaction.c b/sysdeps/unix/sysv/linux/i386/sigaction.c
index 2571f1d..5e43121 100644 (file)
--- a/sysdeps/unix/sysv/linux/i386/sigaction.c
+++ b/sysdeps/unix/sysv/linux/i386/sigaction.c
@@ -148,12 +148,20 @@ __sigaction (int sig, const struct sigaction *act, struct sigaction *oact)
 
 weak_alias (__sigaction, sigaction)
 
+/* NOTE: Please think twice before making any changes to the bits of
+   code below.  GDB needs some intimate knowledge about it to
+   recognize them as signal trampolines, and make backtraces through
+   signal handlers work right.  Important are both the names
+   (__restore and __restore_rt) and the exact instruction sequence.
+   If you ever feel the need to make any changes, please notify the
+   appropriate GDB maintainer.  */
+
 #define RESTORE(name, syscall) RESTORE2 (name, syscall)
 #define RESTORE2(name, syscall) \
 asm                                            \
   (                                            \
    ".align 16\n"                               \
-   "__" #name ":\n"                                    \
+   "__" #name ":\n"                            \
    "   movl $" #syscall ", %eax\n"             \
    "   int  $0x80"                             \
    );
@@ -168,8 +176,8 @@ RESTORE (restore_rt, __NR_rt_sigreturn)
 # define RESTORE2(name, syscall) \
 asm                                            \
   (                                            \
-   ".align 8\n"                                \
-   "__" #name ":\n"                                    \
+   ".align 8\n"                                        \
+   "__" #name ":\n"                            \
    "   popl %eax\n"                            \
    "   movl $" #syscall ", %eax\n"             \
    "   int  $0x80"                             \