commit f610d2935f041c5f41ddcb96924ea42ca2fb5ea5

Author: John David Anglin <danglin@gcc.gnu.org>

Date:   Tue Feb 22 17:28:46 2022 +0000

    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.

    (cherry picked from commit 9e7e5fda38471e00d1190479ea91d7b08ae3e304)

diff --git a/sysdeps/unix/sysv/linux/hppa/getcontext.S b/sysdeps/unix/sysv/linux/hppa/getcontext.S

index c8b690aab8ecc47c..4f2e2587d60effc8 100644

--- a/sysdeps/unix/sysv/linux/hppa/getcontext.S

+++ b/sysdeps/unix/sysv/linux/hppa/getcontext.S

@@ -22,22 +22,28 @@

 #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

@@ -65,13 +71,13 @@ 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)

@@ -90,7 +96,10 @@ 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.  */

@@ -142,13 +151,8 @@ 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 e1ae3aefcaac198d..616405b80c61d531 100644

--- a/sysdeps/unix/sysv/linux/hppa/setcontext.S

+++ b/sysdeps/unix/sysv/linux/hppa/setcontext.S

@@ -76,7 +76,7 @@ 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

@@ -88,6 +88,10 @@ 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 562f00ff0546177d..1664f68c7b9982e8 100644

--- a/sysdeps/unix/sysv/linux/hppa/swapcontext.c

+++ b/sysdeps/unix/sysv/linux/hppa/swapcontext.c

@@ -26,10 +26,6 @@ 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");

@@ -60,7 +56,7 @@ __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");

@@ -68,11 +64,11 @@ __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));