hppa: Revise gettext trampoline design

The current getcontext return trampoline is overly complex and it
unnecessarily clobbers several registers.  By saving the context
pointer (r26) in the context, __getcontext_ret can restore any
registers not restored by setcontext.  This allows getcontext to
save and restore the entire register context present when getcontext
is entered.  We use the unused oR0 context slot for the return
from __getcontext_ret.

While this is not directly useful in C, it can be exploited in
assembly code.  Registers r20, r23, r24 and r25 are not clobbered
in the call path to getcontext.  This allows a small simplification
of swapcontext.

It also allows saving and restoring the 6-bit SAR register in the
LSB of the oSAR context slot.  The getcontext flag value can be
stored in the MSB of the oSAR slot.

diff --git a/sysdeps/unix/sysv/linux/hppa/getcontext.S b/sysdeps/unix/sysv/linux/hppa/getcontext.S
index 6470d73de56c3ec351f143f45d8e78b56be85f71..dcdf986f2dd33cf14fd0e85ed56bf745fa2cd532 100644 (file)
--- a/sysdeps/unix/sysv/linux/hppa/getcontext.S
+++ b/sysdeps/unix/sysv/linux/hppa/getcontext.S
@@ -21,22 +21,28 @@
 #include "ucontext_i.h"
 
 
-       /* Trampoline function. Non-standard calling ABI.  */
+       /* Trampoline function.  Non-standard calling ABI.  */
        /* Can not use ENTRY(__getcontext_ret) here.  */
        .type   __getcontext_ret, @function
        .hidden __getcontext_ret
 __getcontext_ret:
        .proc
        .callinfo FRAME=0,NO_CALLS
-       /* r26-r23 contain original r3-r6, but because setcontext
-          does not reload r3-r6 (it's using them as temporaries)
-          we must save them elsewhere and swap them back in.  */
-       copy    %r23, %r3
-       copy    %r24, %r4
-       copy    %r25, %r5
-       copy    %r26, %r6
-       /* r20 contains original return pointer.  */
-       bv      0(%r20)
+       /* Because setcontext does not reload r3-r6 (it's using them
+          as temporaries), we must load them ourself.  */
+       ldw     oR3(%r26), %r3
+       ldw     oR4(%r26), %r4
+       ldw     oR5(%r26), %r5
+       ldw     oR6(%r26), %r6
+
+       /* Also reload registers clobbered by $$dyncall.  */
+       ldw     oR21(%r26), %r21
+       ldw     oR22(%r26), %r22
+       ldw     oR31(%r26), %r31
+
+       /* oR0 contains original return pointer.  */
+       ldw     oR0(%r26), %rp
+       bv      0(%rp)
        copy    %r0, %ret0
        .procend
        .size   __getcontext_ret, .-__getcontext_ret
@@ -64,13 +70,13 @@ ENTRY(__getcontext)
        stw     %r17, oR17(%r26)
        stw     %r18, oR18(%r26)
        stw     %r19, oR19(%r26)
-       /* stw  %r20, oR20(%r26) - used for trampoline.  */
+       stw     %r20, oR20(%r26)
        stw     %r21, oR21(%r26)
        stw     %r22, oR22(%r26)
-       /* stw  %r23, oR23(%r26) - used for trampoline.  */
-       /* stw  %r24, oR24(%r26) - used for trampoline.  */
-       /* stw  %r25, oR25(%r26) - used for trampoline.  */
-       /* stw  %r26, oR26(%r26) - used for trampoline.  */
+       stw     %r23, oR23(%r26)
+       stw     %r24, oR24(%r26)
+       stw     %r25, oR25(%r26)
+       stw     %r26, oR26(%r26)
        stw     %r27, oR27(%r26)
        stw     %r28, oR28(%r26)
        stw     %r29, oR29(%r26)
@@ -89,7 +95,10 @@ ENTRY(__getcontext)
        stw     %r0, oIASQ1(%r26)
        stw     %r0, oIAOQ0(%r26)
        stw     %r0, oIAOQ1(%r26)
-       stw     %r0, oSAR(%r26) /* used as flag in swapcontext().  */
+
+       /* Save SAR register.  */
+       mfctl   %sar, %r1
+       stw     %r1, oSAR(%r26) /* MSB used as flag in swapcontext().  */
 
 
        /* Store floating-point regs.  */
@@ -141,13 +150,8 @@ ENTRY(__getcontext)
        .cfi_offset 29, 4
 
        /* Set up the trampoline registers.
-          r20, r23, r24, r25, r26 and r2 are clobbered
-          by call to getcontext() anyway. Reuse them.  */
-       stw     %r2, oR20(%r26)
-       stw     %r3, oR23(%r26)
-       stw     %r4, oR24(%r26)
-       stw     %r5, oR25(%r26)
-       stw     %r6, oR26(%r26)
+          Use oR0 context slot to save return value.  */
+       stw     %r2, oR0(%r26)
 #ifdef PIC
        addil   LT%__getcontext_ret, %r19
        ldw     RT%__getcontext_ret(%r1), %r1

diff --git a/sysdeps/unix/sysv/linux/hppa/setcontext.S b/sysdeps/unix/sysv/linux/hppa/setcontext.S
index 5da01c2f356e70cd265e0bef6a97cedc7169d1ff..dfa794ad5c9f1baef35b797e120c1eefdddada03 100644 (file)
--- a/sysdeps/unix/sysv/linux/hppa/setcontext.S
+++ b/sysdeps/unix/sysv/linux/hppa/setcontext.S
@@ -75,7 +75,7 @@ ENTRY(__setcontext)
        ldw     oR18(%r3), %r18
        ldw     oR19(%r3), %r19
        ldw     oR20(%r3), %r20
-       ldw     oR21(%r3), %r21
+       ldw     oR21(%r3), %r21 /* maybe clobbered by dyncall */
        /* ldw  oR22(%r3), %r22 - dyncall arg.  */
        ldw     oR23(%r3), %r23
        ldw     oR24(%r3), %r24
@@ -87,6 +87,10 @@ ENTRY(__setcontext)
        ldw     oR30(%r3), %sp
        /* ldw  oR31(%r3), %r31 - dyncall scratch register */
 
+       /* Restore SAR register.  */
+       ldw     oSAR(%r3), %r22
+       mtsar   %r22
+
        /* Restore floating-point registers.  */
        ldo      oFPREGS31(%r3), %r22
        fldds     0(%r22), %fr31

diff --git a/sysdeps/unix/sysv/linux/hppa/swapcontext.c b/sysdeps/unix/sysv/linux/hppa/swapcontext.c
index 64adb9ee620d6202147e9e9b7763cc55a8c89a18..e5bf6c9933802b86fd061c862e4e082f6fbd1c66 100644 (file)
--- a/sysdeps/unix/sysv/linux/hppa/swapcontext.c
+++ b/sysdeps/unix/sysv/linux/hppa/swapcontext.c
@@ -25,10 +25,6 @@ extern int __setcontext (const ucontext_t *ucp);
 int
 __swapcontext (ucontext_t *oucp, const ucontext_t *ucp)
 {
-  /* Save ucp in stack argument slot.  */
-  asm ("stw %r25,-40(%sp)");
-  asm (".cfi_offset 25, -40");
-
   /* Save rp for debugger.  */
   asm ("stw %rp,-20(%sp)");
   asm (".cfi_offset 2, -20");
@@ -59,7 +55,7 @@ __swapcontext (ucontext_t *oucp, const ucontext_t *ucp)
   asm ("bv,n %r0(%rp)");
 
   /* Load sc_sar flag.  */
-  asm ("ldw %0(%%ret1),%%r20" : : "i" (oSAR));
+  asm ("ldb %0(%%ret1),%%r20" : : "i" (oSAR));
 
   /* Return if oucp context has been reactivated.  */
   asm ("or,= %r0,%r20,%r0");
@@ -67,11 +63,11 @@ __swapcontext (ucontext_t *oucp, const ucontext_t *ucp)
 
   /* Mark sc_sar flag.  */
   asm ("1: ldi 1,%r20");
-  asm ("stw %%r20,%0(%%ret1)" : : "i" (oSAR));
+  asm ("stb %%r20,%0(%%ret1)" : : "i" (oSAR));
 
   /* Activate the machine context in ucp.  */
   asm ("bl __setcontext,%rp");
-  asm ("ldw -40(%sp),%r26");
+  asm ("ldw %0(%%ret1),%%r26" : : "i" (oR25));
 
   /* Load return pointer.  */
   asm ("ldw %0(%%ret1),%%rp" : : "i" (oR28));