When a -fsplit-stack function calls a non-split-stack function, the gold
linker automatically redirects the call to __morestack to call
__morestack_non_split instead. I wrote __morestack_non_split to always
allocate at least 0x4000 bytes. However, that was unclear thinking;
0x4000 bytes is sufficient for calling into libc, but it is not
sufficient for calling a general function. This value leads to stack
overruns in ordinary code. The default thread stack size on x86 and
x86_64 is 0x800000 bytes. This patch significantly increases the stack
size allocated for non-split code, to less than the default but still
larger, 0x100000 bytes.
Probably the program should have a way to control this, but I'm not yet
sure what the right API would be for that. In any case the default
should be larger.
Bootstrapped and ran Go testsuite and split-stack tests on
x86_64-unknown-linux-gnu. Committed to mainline and 4.7 branch.
Ian
2012-08-21 Ian Lance Taylor <i...@google.com>
* config/i386/morestack.S (__morestack_non_split): Increase amount
of space allocated for non-split code stack.
Index: config/i386/morestack.S
===================================================================
--- config/i386/morestack.S (revision 190572)
+++ config/i386/morestack.S (working copy)
@@ -83,6 +83,9 @@
#endif
+# The amount of space we ask for when calling non-split-stack code.
+#define NON_SPLIT_STACK 0x100000
+
# This entry point is for split-stack code which calls non-split-stack
# code. When the linker sees this case, it converts the call to
# __morestack to call __morestack_non_split instead. We just bump the
@@ -109,7 +112,7 @@ __morestack_non_split:
movl %esp,%eax # Current stack,
subl 8(%esp),%eax # less required stack frame size,
- subl $0x4000,%eax # less space for non-split code.
+ subl $NON_SPLIT_STACK,%eax # less space for non-split code.
cmpl %gs:0x30,%eax # See if we have enough space.
jb 2f # Get more space if we need it.
@@ -171,7 +174,8 @@ __morestack_non_split:
.cfi_adjust_cfa_offset -4 # Account for popped register.
- addl $0x5000+BACKOFF,4(%esp) # Increment space we request.
+ # Increment space we request.
+ addl $NON_SPLIT_STACK+0x1000+BACKOFF,4(%esp)
# Fall through into morestack.
@@ -186,7 +190,7 @@ __morestack_non_split:
movq %rsp,%rax # Current stack,
subq %r10,%rax # less required stack frame size,
- subq $0x4000,%rax # less space for non-split code.
+ subq $NON_SPLIT_STACK,%rax # less space for non-split code.
#ifdef __LP64__
cmpq %fs:0x70,%rax # See if we have enough space.
@@ -219,7 +223,8 @@ __morestack_non_split:
.cfi_adjust_cfa_offset -8 # Adjust for popped register.
- addq $0x5000+BACKOFF,%r10 # Increment space we request.
+ # Increment space we request.
+ addq $NON_SPLIT_STACK+0x1000+BACKOFF,%r10
# Fall through into morestack.
