178 lines
5.9 KiB
Diff
178 lines
5.9 KiB
Diff
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commit f610d2935f041c5f41ddcb96924ea42ca2fb5ea5
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Author: John David Anglin <danglin@gcc.gnu.org>
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Date: Tue Feb 22 17:28:46 2022 +0000
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hppa: Revise gettext trampoline design
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The current getcontext return trampoline is overly complex and it
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unnecessarily clobbers several registers. By saving the context
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pointer (r26) in the context, __getcontext_ret can restore any
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registers not restored by setcontext. This allows getcontext to
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save and restore the entire register context present when getcontext
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is entered. We use the unused oR0 context slot for the return
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from __getcontext_ret.
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While this is not directly useful in C, it can be exploited in
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assembly code. Registers r20, r23, r24 and r25 are not clobbered
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in the call path to getcontext. This allows a small simplification
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of swapcontext.
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It also allows saving and restoring the 6-bit SAR register in the
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LSB of the oSAR context slot. The getcontext flag value can be
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stored in the MSB of the oSAR slot.
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(cherry picked from commit 9e7e5fda38471e00d1190479ea91d7b08ae3e304)
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diff --git a/sysdeps/unix/sysv/linux/hppa/getcontext.S b/sysdeps/unix/sysv/linux/hppa/getcontext.S
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index c8b690aab8ecc47c..4f2e2587d60effc8 100644
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--- a/sysdeps/unix/sysv/linux/hppa/getcontext.S
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+++ b/sysdeps/unix/sysv/linux/hppa/getcontext.S
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@@ -22,22 +22,28 @@
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#include "ucontext_i.h"
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- /* Trampoline function. Non-standard calling ABI. */
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+ /* Trampoline function. Non-standard calling ABI. */
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/* Can not use ENTRY(__getcontext_ret) here. */
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.type __getcontext_ret, @function
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.hidden __getcontext_ret
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__getcontext_ret:
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.proc
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.callinfo FRAME=0,NO_CALLS
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- /* r26-r23 contain original r3-r6, but because setcontext
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- does not reload r3-r6 (it's using them as temporaries)
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- we must save them elsewhere and swap them back in. */
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- copy %r23, %r3
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- copy %r24, %r4
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- copy %r25, %r5
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- copy %r26, %r6
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- /* r20 contains original return pointer. */
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- bv 0(%r20)
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+ /* Because setcontext does not reload r3-r6 (it's using them
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+ as temporaries), we must load them ourself. */
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+ ldw oR3(%r26), %r3
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+ ldw oR4(%r26), %r4
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+ ldw oR5(%r26), %r5
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+ ldw oR6(%r26), %r6
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+
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+ /* Also reload registers clobbered by $$dyncall. */
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+ ldw oR21(%r26), %r21
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+ ldw oR22(%r26), %r22
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+ ldw oR31(%r26), %r31
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+
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+ /* oR0 contains original return pointer. */
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+ ldw oR0(%r26), %rp
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+ bv 0(%rp)
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copy %r0, %ret0
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.procend
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.size __getcontext_ret, .-__getcontext_ret
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@@ -65,13 +71,13 @@ ENTRY(__getcontext)
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stw %r17, oR17(%r26)
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stw %r18, oR18(%r26)
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stw %r19, oR19(%r26)
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- /* stw %r20, oR20(%r26) - used for trampoline. */
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+ stw %r20, oR20(%r26)
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stw %r21, oR21(%r26)
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stw %r22, oR22(%r26)
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- /* stw %r23, oR23(%r26) - used for trampoline. */
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- /* stw %r24, oR24(%r26) - used for trampoline. */
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- /* stw %r25, oR25(%r26) - used for trampoline. */
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- /* stw %r26, oR26(%r26) - used for trampoline. */
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+ stw %r23, oR23(%r26)
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+ stw %r24, oR24(%r26)
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+ stw %r25, oR25(%r26)
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+ stw %r26, oR26(%r26)
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stw %r27, oR27(%r26)
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stw %r28, oR28(%r26)
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stw %r29, oR29(%r26)
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@@ -90,7 +96,10 @@ ENTRY(__getcontext)
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stw %r0, oIASQ1(%r26)
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stw %r0, oIAOQ0(%r26)
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stw %r0, oIAOQ1(%r26)
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- stw %r0, oSAR(%r26) /* used as flag in swapcontext(). */
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+
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+ /* Save SAR register. */
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+ mfctl %sar, %r1
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+ stw %r1, oSAR(%r26) /* MSB used as flag in swapcontext(). */
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/* Store floating-point regs. */
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@@ -142,13 +151,8 @@ ENTRY(__getcontext)
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.cfi_offset 29, 4
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/* Set up the trampoline registers.
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- r20, r23, r24, r25, r26 and r2 are clobbered
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- by call to getcontext() anyway. Reuse them. */
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- stw %r2, oR20(%r26)
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- stw %r3, oR23(%r26)
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- stw %r4, oR24(%r26)
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- stw %r5, oR25(%r26)
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- stw %r6, oR26(%r26)
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+ Use oR0 context slot to save return value. */
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+ stw %r2, oR0(%r26)
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#ifdef PIC
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addil LT%__getcontext_ret, %r19
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ldw RT%__getcontext_ret(%r1), %r1
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diff --git a/sysdeps/unix/sysv/linux/hppa/setcontext.S b/sysdeps/unix/sysv/linux/hppa/setcontext.S
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index e1ae3aefcaac198d..616405b80c61d531 100644
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--- a/sysdeps/unix/sysv/linux/hppa/setcontext.S
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+++ b/sysdeps/unix/sysv/linux/hppa/setcontext.S
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@@ -76,7 +76,7 @@ ENTRY(__setcontext)
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ldw oR18(%r3), %r18
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ldw oR19(%r3), %r19
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ldw oR20(%r3), %r20
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- ldw oR21(%r3), %r21
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+ ldw oR21(%r3), %r21 /* maybe clobbered by dyncall */
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/* ldw oR22(%r3), %r22 - dyncall arg. */
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ldw oR23(%r3), %r23
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ldw oR24(%r3), %r24
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@@ -88,6 +88,10 @@ ENTRY(__setcontext)
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ldw oR30(%r3), %sp
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/* ldw oR31(%r3), %r31 - dyncall scratch register */
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+ /* Restore SAR register. */
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+ ldw oSAR(%r3), %r22
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+ mtsar %r22
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+
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/* Restore floating-point registers. */
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ldo oFPREGS31(%r3), %r22
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fldds 0(%r22), %fr31
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diff --git a/sysdeps/unix/sysv/linux/hppa/swapcontext.c b/sysdeps/unix/sysv/linux/hppa/swapcontext.c
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index 562f00ff0546177d..1664f68c7b9982e8 100644
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--- a/sysdeps/unix/sysv/linux/hppa/swapcontext.c
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+++ b/sysdeps/unix/sysv/linux/hppa/swapcontext.c
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@@ -26,10 +26,6 @@ extern int __setcontext (const ucontext_t *ucp);
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int
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__swapcontext (ucontext_t *oucp, const ucontext_t *ucp)
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{
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- /* Save ucp in stack argument slot. */
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- asm ("stw %r25,-40(%sp)");
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- asm (".cfi_offset 25, -40");
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-
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/* Save rp for debugger. */
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asm ("stw %rp,-20(%sp)");
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asm (".cfi_offset 2, -20");
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@@ -60,7 +56,7 @@ __swapcontext (ucontext_t *oucp, const ucontext_t *ucp)
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asm ("bv,n %r0(%rp)");
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/* Load sc_sar flag. */
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- asm ("ldw %0(%%ret1),%%r20" : : "i" (oSAR));
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+ asm ("ldb %0(%%ret1),%%r20" : : "i" (oSAR));
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/* Return if oucp context has been reactivated. */
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asm ("or,= %r0,%r20,%r0");
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@@ -68,11 +64,11 @@ __swapcontext (ucontext_t *oucp, const ucontext_t *ucp)
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/* Mark sc_sar flag. */
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asm ("1: ldi 1,%r20");
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- asm ("stw %%r20,%0(%%ret1)" : : "i" (oSAR));
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+ asm ("stb %%r20,%0(%%ret1)" : : "i" (oSAR));
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/* Activate the machine context in ucp. */
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asm ("bl __setcontext,%rp");
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- asm ("ldw -40(%sp),%r26");
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+ asm ("ldw %0(%%ret1),%%r26" : : "i" (oR25));
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/* Load return pointer. */
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asm ("ldw %0(%%ret1),%%rp" : : "i" (oR28));
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