S/390: Introduce jdd constraint

Implementation of section anchors in S/390 back-end added in r266741
broke jump labels in S/390 Linux kernel [1].  Currently jump labels
pass global variable addresses to .quad directive in inline assembly
using "X" constraint.  In the past this used to produce regular symbol
references, however, after r266741 we sometimes get values like
(plus (reg) (const_int)), where (reg) points to a section anchor.
Strictly speaking, this is still correct, since "X" accepts anything.
Thus, now we need another way to support jump labels.

The existing "i" constraint cannot be used, since with -fPIC it must
not accept non-local symbols, however, jump labels do require that,
e.g. __tracepoint_xdp_exception from kernel proper might be referenced
from kernel modules.

The existing "ZL" constraint cannot be used for the same reason.

The existing "b" constraint cannot be used because of the way
expand_asm_stmt works.  It deduces whether the constraint allows
regs, subregs or mems, and processes asm operands differently based on
that.  "b" is supposed to accept values like (mem (symbol_ref)), and
there appears to be no way to explain to expand_asm_stmt that for "b"
mem's address must not be in a register.

This patch introduces the new machine-specific constraint named "jdd" -
"j" prefix is already used for constants, and "d" stands for "data".
It accepts anything that fits into the data section, whether or not
this might require a relocation, that is, anything that passes
CONSTANT_P check.

[1] https://lkml.org/lkml/2019/1/23/346

gcc/ChangeLog:

2019-02-08  Ilya Leoshkevich  <iii@linux.ibm.com>

	* config/s390/constraints.md (jdd): New constraint.

gcc/testsuite/ChangeLog:

2019-02-08  Ilya Leoshkevich  <iii@linux.ibm.com>

	* gcc.target/s390/jump-label.c: New test.

From-SVN: r268688

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 5e826d097658358d6f20cad5ab568051962dc07c..ef22ae29eb7c8f10b4ae0cb5d500b4fdf93f3a17 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2019-02-08  Ilya Leoshkevich  <iii@linux.ibm.com>
+
+       * config/s390/constraints.md (jdd): New constraint.
+
 2019-02-08  H.J. Lu  <hongjiu.lu@intel.com>
 
        PR target/89229

diff --git a/gcc/config/s390/constraints.md b/gcc/config/s390/constraints.md
index 688dd96e0e27b6427337bf1fbb0b662eed488bbb..4055cbc7c68124f06f3d40e4ad0d22d55898fd3b 100644 (file)
--- a/gcc/config/s390/constraints.md
+++ b/gcc/config/s390/constraints.md
@@ -37,6 +37,7 @@
 ;;         jKK: constant vector with all elements having the same value and
 ;;              matching K constraint
 ;;         jm6: An integer operand with the lowest order 6 bits all ones.
+;;         jdd: A constant operand that fits into the data section.
 ;;    t -- Access registers 36 and 37.
 ;;    v -- Vector registers v0-v31.
 ;;    C -- A signed 8-bit constant (-128..127)
@@ -567,3 +568,19 @@
 (define_constraint "ZL"
   "LARL operand when in 64-bit mode, otherwise nothing."
   (match_test "TARGET_64BIT && larl_operand (op, VOIDmode)"))
+
+;; This constraint must behave like "i", in particular, the matching values
+;; must never be placed into registers or memory by
+;; cfgexpand.c:expand_asm_stmt.  It could be straightforward to start its name
+;; with a letter from genpreds.c:const_int_constraints, however it would
+;; require using (match_code "const_int"), which is infeasible.  To achieve the
+;; same effect, that is, setting maybe_allows_reg and maybe_allows_mem to false
+;; in genpreds.c:add_constraint, we explicitly exclude reg, subreg and mem
+;; codes.
+(define_constraint "jdd"
+  "A constant operand that fits into the data section.
+   Usage of this constraint might produce a relocation."
+  (and (not (match_code "reg"))
+       (not (match_code "subreg"))
+       (not (match_code "mem"))
+       (match_test "CONSTANT_P (op)")))

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 41748579d928333262ac0c149d0d801a51e54674..53ad08a2e58ff088c5ed73bb61e669a213a37b89 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2019-02-08  Ilya Leoshkevich  <iii@linux.ibm.com>
+
+       * gcc.target/s390/jump-label.c: New test.
+
 2019-02-08  Richard Biener  <rguenther@suse.de>
 
        PR testsuite/89250

diff --git a/gcc/testsuite/gcc.target/s390/jump-label.c b/gcc/testsuite/gcc.target/s390/jump-label.c
new file mode 100644 (file)
index 0000000..3de73f6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/jump-label.c
@@ -0,0 +1,19 @@
+/* Test jdd constraint, which is used for linux kernel jump labels.  */
+
+/* { dg-do link } */
+/* { dg-options "-O2 -fPIC -shared" } */
+
+__attribute__ ((visibility ("default"))) extern int i;
+
+void f (void)
+{
+  asm goto (".pushsection foo\n"
+#if defined(__s390x__)
+            ".quad %0-.\n"
+#else
+            ".long %0-.\n"
+#endif
+            ".popsection\n"
+            : : "jdd" (&i) : : l);
+l:;
+}