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[PATCH v2 1/3] aarch64: Re-implement setcontext without rt_sigreturn syscall
- From: Will Newton <will dot newton at linaro dot org>
- To: libc-alpha at sourceware dot org
- Date: Tue, 1 Apr 2014 12:32:45 +0100
- Subject: [PATCH v2 1/3] aarch64: Re-implement setcontext without rt_sigreturn syscall
- Authentication-results: sourceware.org; auth=none
The current implementation of setcontext uses rt_sigreturn to restore
the contents of registers. This contrasts with the way most other
architectures implement setcontext:
powerpc64, mips, tile:
Call rt_sigreturn if context was created by a call to a signal handler,
otherwise restore in user code.
powerpc32:
Call swapcontext system call and don't call sigreturn or rt_sigreturn.
x86_64, sparc, hppa, sh, ia64, m68k, s390, arm:
Only support restoring "synchronous" contexts, that is contexts
created by getcontext, and restoring in user code and don't call
sigreturn or rt_sigreturn.
alpha:
Call sigreturn (but not rt_sigreturn) in all cases to do the restore.
The text of the setcontext manpage suggests that the requirement to be
able to restore a signal handler created context has been dropped from
SUSv2:
If the context was obtained by a call to a signal handler, then old
standard text says that "program execution continues with the program
instruction following the instruction interrupted by the signal".
However, this sentence was removed in SUSv2, and the present verdict
is "the result is unspecified".
Implementing setcontext by calling rt_sigreturn unconditionally causes
problems when used with sigaltstack as in BZ #16629. On this basis it
seems that aarch64 is broken and that new ports should only support
restoring contexts created with getcontext and do not need to call
rt_sigreturn at all.
This patch re-implements the aarch64 setcontext function to restore
the context in user code in a similar manner to x86_64 and other ports.
ChangeLog:
2014-04-01 Will Newton <will.newton@linaro.org>
[BZ #16629]
* sysdeps/unix/sysv/linux/aarch64/setcontext.S (__setcontext):
Re-implement to restore registers in user code and avoid
rt_sigreturn system call.
---
NEWS | 6 +-
sysdeps/unix/sysv/linux/aarch64/setcontext.S | 147 +++++++++++++++++----------
2 files changed, 95 insertions(+), 58 deletions(-)
Changes in v2:
- Added NEWS entry
- Fixed bug in handling sigmask value
- Improved commit message
diff --git a/NEWS b/NEWS
index 1574ab4..219198d 100644
--- a/NEWS
+++ b/NEWS
@@ -11,9 +11,9 @@ Version 2.20
6804, 15347, 15804, 15894, 16002, 16198, 16284, 16348, 16349, 16357,
16362, 16447, 16532, 16545, 16574, 16599, 16600, 16609, 16610, 16611,
- 16613, 16623, 16632, 16634, 16639, 16642, 16648, 16649, 16670, 16674,
- 16677, 16680, 16683, 16689, 16695, 16701, 16706, 16707, 16712, 16713,
- 16714, 16731, 16743, 16758, 16759, 16760, 16770.
+ 16613, 16623, 16629, 16632, 16634, 16639, 16642, 16648, 16649, 16670,
+ 16674, 16677, 16680, 16683, 16689, 16695, 16701, 16706, 16707, 16712,
+ 16713, 16714, 16731, 16743, 16758, 16759, 16760, 16770.
* Running the testsuite no longer terminates as soon as a test fails.
Instead, a file tests.sum (xtests.sum from "make xcheck") is generated,
diff --git a/sysdeps/unix/sysv/linux/aarch64/setcontext.S b/sysdeps/unix/sysv/linux/aarch64/setcontext.S
index d220c41..aef5149 100644
--- a/sysdeps/unix/sysv/linux/aarch64/setcontext.S
+++ b/sysdeps/unix/sysv/linux/aarch64/setcontext.S
@@ -22,68 +22,105 @@
#include "ucontext_i.h"
#include "ucontext-internal.h"
-/* int setcontext (const ucontext_t *ucp) */
+/* int __setcontext (const ucontext_t *ucp)
- .text
-
-ENTRY(__setcontext)
-
- /* Create a signal frame on the stack:
-
- fp
- lr
- ...
- sp-> rt_sigframe
- */
-
- stp x29, x30, [sp, -16]!
- cfi_adjust_cfa_offset (16)
- cfi_rel_offset (x29, 0)
- cfi_rel_offset (x30, 8)
-
- mov x29, sp
- cfi_def_cfa_register (x29)
-
- /* Allocate space for the sigcontext. */
- mov w3, #((RT_SIGFRAME_SIZE + SP_ALIGN_SIZE) & SP_ALIGN_MASK)
- sub sp, sp, x3
+ Restores the machine context in UCP and thereby resumes execution
+ in that context.
- /* Compute the base address of the ucontext structure. */
- add x1, sp, #RT_SIGFRAME_UCONTEXT
+ This implementation is intended to be used for *synchronous* context
+ switches only. Therefore, it does not have to restore anything
+ other than the PRESERVED state. */
- /* Only ucontext is required in the frame, *copy* it in. */
-
-#if UCONTEXT_SIZE % 16
-#error The implementation of setcontext.S assumes sizeof(ucontext_t) % 16 == 0
-#endif
-
- mov x2, #UCONTEXT_SIZE / 16
-0:
- ldp x3, x4, [x0], #16
- stp x3, x4, [x1], #16
- sub x2, x2, 1
- cbnz x2, 0b
+ .text
- /* rt_sigreturn () -- no arguments, sp points to struct rt_sigframe. */
- mov x8, SYS_ify (rt_sigreturn)
+ENTRY (__setcontext)
+ /* Save a copy of UCP. */
+ mov x9, x0
+
+ /* Set the signal mask with
+ rt_sigprocmask (SIG_SETMASK, mask, NULL, _NSIG/8). */
+ mov x0, #SIG_SETMASK
+ add x1, x9, #UCONTEXT_SIGMASK
+ mov x2, #0
+ mov x3, #_NSIG8
+ mov x8, SYS_ify (rt_sigprocmask)
svc 0
-
- /* Ooops we failed. Recover the stack */
-
- mov sp, x29
- cfi_def_cfa_register (sp)
-
- ldp x29, x30, [sp], 16
- cfi_adjust_cfa_offset (16)
- cfi_restore (x29)
- cfi_restore (x30)
- b C_SYMBOL_NAME(__syscall_error)
-
+ cbz x0, 1f
+ b C_SYMBOL_NAME (__syscall_error)
+1:
+ /* Restore the general purpose registers. */
+ mov x0, x9
+ cfi_def_cfa (x0, 0)
+ cfi_offset (x18, oX0 + 18 * SZREG)
+ cfi_offset (x19, oX0 + 19 * SZREG)
+ cfi_offset (x20, oX0 + 20 * SZREG)
+ cfi_offset (x21, oX0 + 21 * SZREG)
+ cfi_offset (x22, oX0 + 22 * SZREG)
+ cfi_offset (x23, oX0 + 23 * SZREG)
+ cfi_offset (x24, oX0 + 24 * SZREG)
+ cfi_offset (x25, oX0 + 25 * SZREG)
+ cfi_offset (x26, oX0 + 26 * SZREG)
+ cfi_offset (x27, oX0 + 27 * SZREG)
+ cfi_offset (x28, oX0 + 28 * SZREG)
+ cfi_offset (x29, oX0 + 29 * SZREG)
+ cfi_offset (x30, oX0 + 30 * SZREG)
+
+ cfi_offset ( d8, oV0 + 8 * SZVREG)
+ cfi_offset ( d9, oV0 + 9 * SZVREG)
+ cfi_offset (d10, oV0 + 10 * SZVREG)
+ cfi_offset (d11, oV0 + 11 * SZVREG)
+ cfi_offset (d12, oV0 + 12 * SZVREG)
+ cfi_offset (d13, oV0 + 13 * SZVREG)
+ cfi_offset (d14, oV0 + 14 * SZVREG)
+ cfi_offset (d15, oV0 + 15 * SZVREG)
+ ldp x18, x19, [x0, oX0 + 18 * SZREG]
+ ldp x20, x21, [x0, oX0 + 20 * SZREG]
+ ldp x22, x23, [x0, oX0 + 22 * SZREG]
+ ldp x24, x25, [x0, oX0 + 24 * SZREG]
+ ldp x26, x27, [x0, oX0 + 26 * SZREG]
+ ldp x28, x29, [x0, oX0 + 28 * SZREG]
+ ldr x30, [x0, oX0 + 30 * SZREG]
+ ldr x2, [x0, oSP]
+ mov sp, x2
+
+ /* Check for FP SIMD context. */
+ add x2, x0, #oEXTENSION
+
+ mov w3, #(FPSIMD_MAGIC & 0xffff)
+ movk w3, #(FPSIMD_MAGIC >> 16), lsl #16
+ ldr w1, [x2, #oHEAD + oMAGIC]
+ cmp w1, w3
+ b.ne 2f
+
+ /* Restore the FP SIMD context. */
+ add x3, x2, #oV0 + 8 * SZVREG
+ ldp d8, d9, [x3], #2 * SZVREG
+ ldp d10, d11, [x3], #2 * SZVREG
+ ldp d12, d13, [x3], #2 * SZVREG
+ ldp d14, d15, [x3], #2 * SZVREG
+
+ add x3, x2, oFPSR
+
+ ldr w4, [x3]
+ msr fpsr, x4
+
+ ldr w4, [x3, oFPCR - oFPSR]
+ msr fpcr, x4
+
+2:
+ ldr x16, [x0, oPC]
+ /* Restore arg registers. */
+ ldp x2, x3, [x0, oX0 + 2 * SZREG]
+ ldp x4, x5, [x0, oX0 + 4 * SZREG]
+ ldp x6, x7, [x0, oX0 + 6 * SZREG]
+ ldp x0, x1, [x0, oX0 + 0 * SZREG]
+ /* Jump to the new pc value. */
+ br x16
PSEUDO_END (__setcontext)
weak_alias (__setcontext, setcontext)
-ENTRY(__startcontext)
+ENTRY (__startcontext)
mov x0, x19
cbnz x0, __setcontext
-1: b HIDDEN_JUMPTARGET(_exit)
-END(__startcontext)
+1: b HIDDEN_JUMPTARGET (_exit)
+END (__startcontext)
--
1.8.1.4