[commit: ghc] master: Fix incorrect stack pointer usage in StgRun() on x86_64 (b38ee89)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/b38ee89c8c8724ba2feb98d4082795a5d4ae96f6/ghc

>---------------------------------------------------------------

commit b38ee89c8c8724ba2feb98d4082795a5d4ae96f6
Author: Ben Gamari <bgamari.foss at gmail.com>
Date:   Mon Aug 3 08:42:00 2015 +0200

    Fix incorrect stack pointer usage in StgRun() on x86_64
    
    The STG_RETURN code from StgCRun.c is incorrect for x86_64 variants
    where the ABI doesn't impose a mandatory red zone for the stack, like on
    Windows or Xen/HaLVM. The current implementation restores the stack
    pointer first, which effectively marks the area with the saved registers
    as reusable. Later, the CPU registers are restored from this "free"
    area.
    
    This ordering happens to work by accident on operating systems that
    strictly adhere to the System V ABI, because any interrupt/signal
    delivery is guaranteed to leave the first 128 bytes past the stack
    pointer untouched (red zone). On other systems this might result in
    corrupted CPU registers if an interruption happens just after restoring
    the stack pointer.
    
    The red zone is usually only used by small leaf functions to avoid
    updates to the stack pointer and exploiting it doesn't give us any
    advantage in this case.
    
    Reviewers: austin, rwbarton
    
    Reviewed By: rwbarton
    
    Subscribers: thomie, simonmar
    
    Differential Revision: https://phabricator.haskell.org/D1120
    
    GHC Trac Issues: #10155


>---------------------------------------------------------------

b38ee89c8c8724ba2feb98d4082795a5d4ae96f6
 rts/StgCRun.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/rts/StgCRun.c b/rts/StgCRun.c
index 2903911..6448509 100644
--- a/rts/StgCRun.c
+++ b/rts/StgCRun.c
@@ -302,19 +302,18 @@ StgRunIsImplementedInAssembler(void)
          * restore callee-saves registers.  (Don't stomp on %%rax!)
          */
         "addq %0, %%rsp\n\t"
-        "movq %%rsp, %%rdx\n\t"
-        "addq %1, %%rsp\n\t"
-        "movq 0(%%rdx),%%rbx\n\t"       /* restore the registers saved above */
-        "movq 8(%%rdx),%%rbp\n\t"
-        "movq 16(%%rdx),%%r12\n\t"
-        "movq 24(%%rdx),%%r13\n\t"
-        "movq 32(%%rdx),%%r14\n\t"
-        "movq 40(%%rdx),%%r15\n\t"
+        "movq 0(%%rsp),%%rbx\n\t"       /* restore the registers saved above */
+        "movq 8(%%rsp),%%rbp\n\t"
+        "movq 16(%%rsp),%%r12\n\t"
+        "movq 24(%%rsp),%%r13\n\t"
+        "movq 32(%%rsp),%%r14\n\t"
+        "movq 40(%%rsp),%%r15\n\t"
 #if defined(mingw32_HOST_OS)
-        "movq 48(%%rdx),%%rdi\n\t"
-        "movq 56(%%rdx),%%rsi\n\t"
-        "movq 64(%%rdx),%%xmm6\n\t"
+        "movq 48(%%rsp),%%rdi\n\t"
+        "movq 56(%%rsp),%%rsi\n\t"
+        "movq 64(%%rsp),%%xmm6\n\t"
 #endif
+        "addq %1, %%rsp\n\t"
         "retq"
 
         :