Commit 45bb77c6 authored by panne's avatar panne

[project @ 2004-08-22 16:20:42 by panne]

* Renamed __obscure_ccall_ret_code to obscure_ccall_ret_code, leading
  underscores are bad for user code.

* Let the code for obscure_ccall_ret_code live in dynamically
  allocated memory, just like the adjustors. This should fix problems
  on OpenBSD, which doesn't like executable code in the data section.
parent 47ff0630
......@@ -88,34 +88,8 @@ execPage (void* addr, pageMode mode)
#endif
}
static unsigned char __obscure_ccall_ret_code [] =
#if defined(i386_TARGET_ARCH)
/* Now here's something obscure for you:
When generating an adjustor thunk that uses the C calling
convention, we have to make sure that the thunk kicks off
the process of jumping into Haskell with a tail jump. Why?
Because as a result of jumping in into Haskell we may end
up freeing the very adjustor thunk we came from using
freeHaskellFunctionPtr(). Hence, we better not return to
the adjustor code on our way out, since it could by then
point to junk.
The fix is readily at hand, just include the opcodes
for the C stack fixup code that we need to perform when
returning in some static piece of memory and arrange
to return to it before tail jumping from the adjustor thunk.
For this to work we make the assumption that bytes in .data
are considered executable.
*/
{ 0x83, 0xc4, 0x04 /* addl $0x4, %esp */
, 0xc3 /* ret */
};
#else
/* No such mind-twisters on non-Intel platforms */
{ };
static unsigned char *obscure_ccall_ret_code;
#endif
#if defined(alpha_TARGET_ARCH)
......@@ -208,7 +182,7 @@ createAdjustor(int cconv, StgStablePtr hptr, StgFunPtr wptr)
<00>: 68 ef be ad de pushl $0xdeadbeef # constant is large enough to
# hold a StgStablePtr
<05>: b8 fa ef ff 00 movl $0x00ffeffa, %eax # load up wptr
<0a>: 68 ef be ad de pushl $__obscure_ccall_ret_code # push the return address
<0a>: 68 ef be ad de pushl $obscure_ccall_ret_code # push the return address
<0f>: ff e0 jmp *%eax # jump to wptr
The ccall'ing version is a tad different, passing in the return
......@@ -216,7 +190,7 @@ createAdjustor(int cconv, StgStablePtr hptr, StgFunPtr wptr)
via the stable pointer.) (The auto-generated C stub is in on this
game, don't worry :-)
See the comment next to __obscure_ccall_ret_code why we need to
See the comment next to obscure_ccall_ret_code why we need to
perform a tail jump instead of a call, followed by some C stack
fixup.
......@@ -234,8 +208,8 @@ createAdjustor(int cconv, StgStablePtr hptr, StgFunPtr wptr)
adj_code[0x05] = (unsigned char)0xb8; /* movl $wptr, %eax */
*((StgFunPtr*)(adj_code + 0x06)) = (StgFunPtr)wptr;
adj_code[0x0a] = (unsigned char)0x68; /* pushl __obscure_ccall_ret_code */
*((StgFunPtr*)(adj_code + 0x0b)) = (StgFunPtr)__obscure_ccall_ret_code;
adj_code[0x0a] = (unsigned char)0x68; /* pushl obscure_ccall_ret_code */
*((StgFunPtr*)(adj_code + 0x0b)) = (StgFunPtr)obscure_ccall_ret_code;
adj_code[0x0f] = (unsigned char)0xff; /* jmp *%eax */
adj_code[0x10] = (unsigned char)0xe0;
......@@ -587,5 +561,33 @@ freeHaskellFunctionPtr(void* ptr)
rtsBool
initAdjustor(void)
{
return execPage(__obscure_ccall_ret_code, pageExecuteRead);
#if defined(i386_TARGET_ARCH)
/* Now here's something obscure for you:
When generating an adjustor thunk that uses the C calling
convention, we have to make sure that the thunk kicks off
the process of jumping into Haskell with a tail jump. Why?
Because as a result of jumping in into Haskell we may end
up freeing the very adjustor thunk we came from using
freeHaskellFunctionPtr(). Hence, we better not return to
the adjustor code on our way out, since it could by then
point to junk.
The fix is readily at hand, just include the opcodes
for the C stack fixup code that we need to perform when
returning in some static piece of memory and arrange
to return to it before tail jumping from the adjustor thunk.
*/
obscure_ccall_ret_code = stgMallocBytes(4, "initAdjustor");
obscure_ccall_ret_code[0x00] = (unsigned char)0x83; /* addl $0x4, %esp */
obscure_ccall_ret_code[0x01] = (unsigned char)0xc4;
obscure_ccall_ret_code[0x02] = (unsigned char)0x04;
obscure_ccall_ret_code[0x03] = (unsigned char)0xc3; /* ret */
execPage(obscure_ccall_ret_code, pageExecuteRead);
#endif
return rtsTrue;
}
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