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Re: [patch] for PR 28281: enable -fstack-protector for the x86_64 linux kernel
2006-07-06 Arjan van de Ven <arjan@linux.intel.com>
* config/i386/i386.md (stack_tls_protect_set_di,
stack_tls_protect_test_di): Use %gs rather than %fs for
-mcmodel=kernel.
* gcc.target/i386/stack-prot-kernel.c: New test.
This is OK if you add a comment to the two insns you are modifying in
i386.md which explains why the kernel uses a different segment
register (one insn can simply refer to the other insns if you like).
E.g., /* The kernel uses a different segment register for performance
reasons: a system call will not have to trash the userspace segment
register, which would be expensive. */
Approved with that change.
patch with added comments below
2006-07-06 Arjan van de Ven <arjan@linux.intel.com>
* config/i386/i386.md (stack_tls_protect_set_di,
stack_tls_protect_test_di): Use %gs rather than %fs for
-mcmodel=kernel.
* gcc.target/i386/stack-prot-kernel.c: New test.
Index: gcc/testsuite/gcc.target/i386/stack-prot-kernel.c
===================================================================
--- gcc/testsuite/gcc.target/i386/stack-prot-kernel.c (revision 0)
+++ gcc/testsuite/gcc.target/i386/stack-prot-kernel.c (revision 0)
@@ -0,0 +1,12 @@
+/* { dg-do compile { target lp64 } } */
+/* { dg-options "-O2 -fstack-protector-all -mcmodel=kernel" } */
+
+void test1 (int x)
+{
+ char p[40];
+ int i;
+ for (i=0; i<40; i++)
+ p[i] = x;
+}
+
+/* { dg-final { scan-assembler-not "%fs" } } */
Index: gcc/config/i386/i386.md
===================================================================
--- gcc/config/i386/i386.md (revision 115220)
+++ gcc/config/i386/i386.md (working copy)
@@ -20393,7 +20393,14 @@
(set (match_scratch:DI 2 "=&r") (const_int 0))
(clobber (reg:CC FLAGS_REG))]
"TARGET_64BIT"
- "mov{q}\t{%%fs:%P1, %2|%2, QWORD PTR %%fs:%P1}\;mov{q}\t{%2, %0|%0, %2}\;xor{l}\t%k2, %k2"
+ {
+ /* The kernel uses a different segment register for performance reasons; a system call
+ would not have to trash the userspace segment register, which would be expensive */
+ if (ix86_cmodel != CM_KERNEL)
+ return "mov{q}\t{%%fs:%P1, %2|%2, QWORD PTR %%fs:%P1}\;mov{q}\t{%2, %0|%0, %2}\;xor{l}\t%k2, %k2";
+ else
+ return "mov{q}\t{%%gs:%P1, %2|%2, QWORD PTR %%gs:%P1}\;mov{q}\t{%2, %0|%0, %2}\;xor{l}\t%k2, %k2";
+ }
[(set_attr "type" "multi")])
(define_expand "stack_protect_test"
@@ -20461,7 +20468,14 @@
UNSPEC_SP_TLS_TEST))
(clobber (match_scratch:DI 3 "=r"))]
"TARGET_64BIT"
- "mov{q}\t{%1, %3|%3, %1}\;xor{q}\t{%%fs:%P2, %3|%3, QWORD PTR %%fs:%P2}"
+ {
+ /* The kernel uses a different segment register for performance reasons; a system call
+ would not have to trash the userspace segment register, which would be expensive */
+ if (ix86_cmodel != CM_KERNEL)
+ return "mov{q}\t{%1, %3|%3, %1}\;xor{q}\t{%%fs:%P2, %3|%3, QWORD PTR %%fs:%P2}";
+ else
+ return "mov{q}\t{%1, %3|%3, %1}\;xor{q}\t{%%gs:%P2, %3|%3, QWORD PTR %%gs:%P2}";
+ }
[(set_attr "type" "multi")])
(include "sse.md")