Safe all clobbered volatile registers when using alternate stack

	* exceptions.cc (_cygtls::call_signal_handler): Drop subtracting 16
	bytes from the alternate stack, it's not necessary.  Safe all clobbered
	registers.  Safe one on the orignal stack, the others on the alternate
	stack on both platforms.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

1 files changed, 47 insertions, 22 deletions

diff --git a/winsup/cygwin/exceptions.cc b/winsup/cygwin/exceptions.cc
index fb59c6142..8d341799e 100644
--- a/winsup/cygwin/exceptions.cc
+++ b/winsup/cygwin/exceptions.cc
@@ -1594,29 +1594,49 @@ _cygtls::call_signal_handler ()
 	    If the current code does not work as expected in the "usual"
 	    POSIX circumstances, this problem must be revisited. */
 
-	  /* Compute new stackbase.  We start from the high address, subtract
-	     16 bytes (safe/sorry) and align to 16 byte. */
+	  /* Compute new stackbase.  We start from the high address, aligned
+	     to 16 byte. */
 	  uintptr_t new_sp = (uintptr_t) _my_tls.altstack.ss_sp
-			     + _my_tls.altstack.ss_size - 0x10;
+			     + _my_tls.altstack.ss_size;
 	  new_sp &= ~0xf;
 	  /* Mark alternate stack as used. */
 	  _my_tls.altstack.ss_flags = SS_ONSTACK;
-	  /* Move to alternate stack, call thisfunc, revert stack regs. */
+	  /* In assembler: Save regs on new stack, move to alternate stack,
+	     call thisfunc, revert stack regs. */
 #ifdef __x86_64__
+	  /* Clobbered regs: rax, rcx, rdx, r8, r9, r10, r11, rbp, rsp */
 	  __asm__ ("\n\
-		   movq  %[NEW_SP], %%r10  # Load alt stack into r10	\n\
+		   pushq %%r9              # Push r9 on orig stack 	\n\
+		   movq  %[NEW_SP], %%r9   # Load alt stack into r9	\n\
+		   subq  $0x40, %%r9       # Make room on alt stack to	\n\
+					   # save clobbered regs	\n\
+		   movq  %%rax, (%%r9)     # Save other clobbered regs	\n\
+		   movq  %%rcx, 0x8(%%r9)				\n\
+		   movq  %%rdx, 0x10(%%r9)				\n\
+		   movq  %%r8,  0x18(%%r9)				\n\
+		   movq  %%r10, 0x20(%%r9)				\n\
+		   movq  %%r11, 0x28(%%r9)				\n\
+		   movq  %%rbp, 0x30(%%r9)				\n\
+		   movq  %%rsp, 0x38(%%r9)				\n\
 		   movl  %[SIG], %%ecx     # thissig to 1st arg reg	\n\
 		   movq  %[SI], %%rdx      # &thissi to 2nd arg reg	\n\
 		   movq  %[CTX], %%r8      # thiscontext to 3rd arg reg	\n\
 		   movq  %[FUNC], %%rax    # thisfunc to rax		\n\
-		   movq  %%rbp, %%r12      # Save rbp in r12		\n\
-		   movq  %%rsp, %%r13      # Save rsp in r13		\n\
-		   movq  %%r10, %%rsp      # Move alt stack into rsp	\n\
+		   movq  %%r9, %%rsp       # Move alt stack into rsp	\n\
 		   xorq  %%rbp, %%rbp      # Set rbp to 0		\n\
-		   subq  $32, %%rsp        # Setup shadow space		\n\
+		   subq  $0x20, %%rsp      # Setup shadow space		\n\
 		   call  *%%rax            # Call thisfunc		\n\
-		   movq  %%r12, %%rbp      # Restore rbp		\n\
-		   movq  %%r13, %%rsp      # Restore rsp		\n"
+		   addq  $0x20, %%rsp      # Revert shadow space	\n\
+		   movq  %%rsp, %%r9       # Restore clobbered regs	\n\
+		   movq  0x38(%%r9), %%rsp				\n\
+		   movq  0x30(%%r9), %%rbp				\n\
+		   movq  0x28(%%r9), %%r11				\n\
+		   movq  0x20(%%r9), %%r10				\n\
+		   movq  0x18(%%r9), %%r8				\n\
+		   movq  0x10(%%r9), %%rdx				\n\
+		   movq  0x8(%%r9), %%rcx				\n\
+		   movq  (%%r9), %%rax					\n\
+		   popq  %%r9						\n"
 		   : : [NEW_SP]	"o" (new_sp),
 		       [SIG]	"o" (thissig),
 		       [SI]	"p" (&thissi),
@@ -1624,11 +1644,17 @@ _cygtls::call_signal_handler ()
 		       [FUNC]	"o" (thisfunc)
 		   : "memory");
 #else
+	  /* Clobbered regs: eax, ecx, edx, ebp, esp */
 	  __asm__ ("\n\
-		   push  %%ecx             # Save ecx on orig stack	\n\
-		   push  %%edx             # Save edx on orig stack	\n\
+		   push  %%ecx             # Push ecx on orig stack	\n\
 		   movl  %[NEW_SP], %%ecx  # Load alt stack into ecx	\n\
-		   subl  $20, %%ecx        # Make room on new stack	\n\
+		   subl  $28, %%ecx        # Make room on alt stack for	\n\
+					   # clobbered regs and args to \n\
+					   # signal handler             \n\
+		   movl  %%eax, 12(%%ecx)  # Save other clobbered regs	\n\
+		   movl  %%edx, 16(%%ecx)				\n\
+		   movl  %%ebp, 20(%%ecx)				\n\
+		   movl  %%esp, 24(%%ecx)				\n\
 		   movl  %[SIG], %%edx     # thissig to 1st arg slot	\n\
 		   movl  %%edx, (%%ecx)					\n\
 		   movl  %[SI], %%edx      # &thissi to 2nd arg slot	\n\
@@ -1636,16 +1662,15 @@ _cygtls::call_signal_handler ()
 		   movl  %[CTX], %%edx     # thiscontext to 3rd arg slot\n\
 		   movl  %%edx, 8(%%ecx)				\n\
 		   movl  %[FUNC], %%eax    # thisfunc to eax		\n\
-		   movl  %%ebp, 12(%%ecx)  # Save ebp on alt stack	\n\
-		   movl  %%esp, 16(%%ecx)  # Save esp on alt stack	\n\
-		   movl  %%ecx, %%esp      # Move stackbase into esp	\n\
+		   movl  %%ecx, %%esp      # Move alt stack into esp	\n\
 		   xorl  %%ebp, %%ebp      # Set ebp to 0		\n\
 		   call  *%%eax            # Call thisfunc		\n\
-		   movl	 %%esp, %%ecx      # Move alt stack to ecx	\n\
-		   movl	 12(%%ecx), %%ebp  # Restore ebp		\n\
-		   movl  16(%%ecx), %%esp  # Restore esp		\n\
-		   popl  %%edx             # Restore edx from orig stack\n\
-		   popl  %%ecx             # Restore ecx from orig stack\n"
+		   movl	 %%esp, %%ecx      # Restore clobbered regs	\n\
+		   movl  24(%%ecx), %%esp				\n\
+		   movl	 20(%%ecx), %%ebp				\n\
+		   movl	 16(%%ecx), %%edx				\n\
+		   movl	 12(%%ecx), %%eax				\n\
+		   popl  %%ecx						\n"
 		   : : [NEW_SP]	"o" (new_sp),
 		       [SIG]	"o" (thissig),
 		       [SI]	"p" (&thissi),