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>

diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 4591d4aac27af750dff76808369f2a35cb5af129..6b01539ea53771af11f07cc5ab69284ef2bce109 100644 (file)
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,10 @@
+2015-06-21  Corinna Vinschen  <corinna@vinschen.de>
+
+       * 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.
+
 2015-06-20  Corinna Vinschen  <corinna@vinschen.de>
 
        * exceptions.cc (_cygtls::call_signal_handler): Implement alternate

diff --git a/winsup/cygwin/exceptions.cc b/winsup/cygwin/exceptions.cc
index fb59c614269c156a9ee3f201dda9f080822ce8af..8d341799e370d737069315a8b438401a640377dc 100644 (file)
--- 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),