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0023-hppa-Revise-gettext-trampoline-design.patch
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0023-hppa-Revise-gettext-trampoline-design.patch
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From d82d9cdff40492d46f75d5d12b3c9e2ac0c422fe Mon Sep 17 00:00:00 2001
From: John David Anglin <[email protected]>
Date: Tue, 22 Feb 2022 17:28:46 +0000
Subject: [PATCH 23/28] 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)
---
sysdeps/unix/sysv/linux/hppa/getcontext.S | 50 ++++++++++++----------
sysdeps/unix/sysv/linux/hppa/setcontext.S | 6 ++-
sysdeps/unix/sysv/linux/hppa/swapcontext.c | 10 ++---
3 files changed, 35 insertions(+), 31 deletions(-)
diff --git a/sysdeps/unix/sysv/linux/hppa/getcontext.S b/sysdeps/unix/sysv/linux/hppa/getcontext.S
index 6470d73de5..dcdf986f2d 100644
--- 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 5da01c2f35..dfa794ad5c 100644
--- 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 64adb9ee62..e5bf6c9933 100644
--- 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));
--
2.33.1