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authorChris Zankel <chris@zankel.net>2012-12-05 14:00:44 -0800
committerChris Zankel <chris@zankel.net>2012-12-05 14:25:07 -0800
commitf4b1b7ade7971141aa3bf731894053696b0ca4e9 (patch)
tree70497675a676628d409090329da6a76ccc03d4e7 /libc/sysdeps
parentae9e3f46520c35dd77f7f2a26f789a94276e6a8c (diff)
xtensa: fix setjmp that didn't save all registers correctly
Setjmp was only saving the lower order of registers (a0-a3) correctly, but not the higher ones (a4-a8/a12). The change also includes additional information, and renames many of the registers, so that setjmp and longjmp look more like the inverse of each other. Signed-off-by: Chris Zankel <chris@zankel.net>
Diffstat (limited to 'libc/sysdeps')
-rw-r--r--libc/sysdeps/linux/xtensa/setjmp.S150
1 files changed, 86 insertions, 64 deletions
diff --git a/libc/sysdeps/linux/xtensa/setjmp.S b/libc/sysdeps/linux/xtensa/setjmp.S
index aac27406c..bf4691294 100644
--- a/libc/sysdeps/linux/xtensa/setjmp.S
+++ b/libc/sysdeps/linux/xtensa/setjmp.S
@@ -24,24 +24,52 @@
then sets things up so that it will return to the right place,
using a window underflow to automatically restore the registers.
- Note that it would probably be sufficient to only copy the
- registers from setjmp's caller into jmp_buf. However, we also copy
- the save area located at the stack pointer of setjmp's caller.
- This save area will typically remain intact until the longjmp call.
- The one exception is when there is an intervening alloca in
- setjmp's caller. This is certainly an unusual situation and is
- likely to cause problems in any case (the storage allocated on the
- stack cannot be safely accessed following the longjmp). As bad as
- it is, on most systems this situation would not necessarily lead to
- a catastrophic failure. If we did not preserve the extra save area
- on Xtensa, however, it would. When setjmp's caller returns after a
- longjmp, there will be a window underflow; an invalid return
- address or stack pointer in the save area will almost certainly
- lead to a crash. Keeping a copy of the extra save area in the
- jmp_buf avoids this with only a small additional cost. If setjmp
- and longjmp are ever time-critical, this could be removed. */
+ Note that we also save the area located just below the stack pointer
+ of the caller. This save area could get overwritten by alloca
+ following the call to setjmp. The alloca moves the stack pointer
+ to allocate memory on the stack. This newly allocated memory
+ includes(!) the original save area (alloca copies the save area
+ before it moves that stack pointer).
+
+
+ previous caller SP -> |------------------------------| <-----+
+ | caller-2 registers a0-a3 | | p
+ |------------------------------| | o
+ | caller registers a4-a8/a12 | | i
+ |------------------------------| | n
+ | caller local stack | | t
+ caller SP -> |------------------------------| <-+ | s
+ | caller-1 registers a0-a3 | -:---+
+ callee (setjmp) SP -> |==============================| |
+ | caller registers a0-a3 | --+
+ |------------------------------|
+
+ In case of an alloca, registers a0-a3 of the previous caller (caller-1)
+ are copied (*), and the original location get likely overwritten.
+
+ previous caller SP -> |------------------------------| <-----+
+ | caller-2 registers a0-a3 | | p
+ |------------------------------| | o
+ | caller registers a4-a8/a12 | | i
+ |------------------------------| | n
+ | caller local stack | | t
+ caller SP before alloca-> |------------------------------| | s
+ | alloca area (overwrites old | |
+ | copy of caller-1 registers) | |
+ caller SP after alloca -> |------------------------------| <-+ |
+ | caller-1 registers a0-a3 (*) | -:---+
+ callee (setjmp) SP -> |==============================| |
+ | caller registers a0-a3 | --+
+ |------------------------------|
+
+ So, when longcall returns to the original caller SP, it also needs
+ to restore the save area below the SP.
+
+ */
#include "sysdep.h"
+
+/* NOTE: The ENTRY macro must allocate exactly 16 bytes (entry a1, 16) */
/* int setjmp (a2 = jmp_buf env) */
@@ -56,8 +84,7 @@ ENTRY (setjmp)
j 1f
END (setjmp)
-/* int __sigsetjmp (a2 = jmp_buf env,
- a3 = int savemask) */
+/* int __sigsetjmp (a2 = jmp_buf env, a3 = int savemask) */
ENTRY (__sigsetjmp)
1:
@@ -65,61 +92,56 @@ ENTRY (__sigsetjmp)
movi a4, __window_spill
callx4 a4
- /* Preserve the second argument (savemask) in a15. The selection
- of a15 is arbitrary, except it's otherwise unused. There is no
- risk of triggering a window overflow since we just returned
- from __window_spill(). */
- mov a15, a3
-
- /* Copy the register save area at (sp - 16). */
- addi a5, a1, -16
- l32i a3, a5, 0
- l32i a4, a5, 4
- s32i a3, a2, 0
- s32i a4, a2, 4
- l32i a3, a5, 8
- l32i a4, a5, 12
- s32i a3, a2, 8
- s32i a4, a2, 12
-
- /* Copy 0-8 words from the register overflow area. */
- extui a3, a0, 30, 2
- blti a3, 2, .Lendsj
- l32i a7, a5, 4
- slli a4, a3, 4
- sub a5, a7, a4
- addi a6, a2, 16
- addi a7, a7, -16 /* a7 = end of register overflow area */
+ /* Copy the caller register a0-a3 at (sp - 16) to jmpbuf. */
+ addi a7, a1, -16
+ l32i a4, a7, 0
+ l32i a5, a7, 4
+ s32i a4, a2, 0
+ s32i a5, a2, 4
+ l32i a4, a7, 8
+ l32i a5, a7, 12
+ s32i a4, a2, 8
+ s32i a5, a2, 12
+
+ /* Copy the caller registers a4-a8/a12 from the overflow area. */
+ /* Note that entry moved the SP by 16B, so SP of caller-1 is at 4(sp) */
+ extui a7, a0, 30, 2
+ blti a7, 2, .Lendsj
+ l32i a8, a1, 4 /* a8: SP of 'caller-1' */
+ slli a4, a7, 4
+ sub a6, a8, a4
+ addi a5, a2, 16
+ addi a8, a8, -16 /* a8: end of register overflow area */
.Lsjloop:
- l32i a3, a5, 0
- l32i a4, a5, 4
- s32i a3, a6, 0
- s32i a4, a6, 4
- l32i a3, a5, 8
- l32i a4, a5, 12
- s32i a3, a6, 8
- s32i a4, a6, 12
- addi a5, a5, 16
+ l32i a7, a6, 0
+ l32i a4, a6, 4
+ s32i a7, a5, 0
+ s32i a4, a5, 4
+ l32i a7, a6, 8
+ l32i a4, a6, 12
+ s32i a7, a5, 8
+ s32i a4, a5, 12
+ addi a5, a6, 16
addi a6, a6, 16
- blt a5, a7, .Lsjloop
+ blt a6, a8, .Lsjloop
.Lendsj:
- /* Copy the register save area at sp. */
- l32i a3, a1, 0
- l32i a4, a1, 4
- s32i a3, a2, 48
- s32i a4, a2, 52
- l32i a3, a1, 8
- l32i a4, a1, 12
- s32i a3, a2, 56
- s32i a4, a2, 60
+ /* Copy previous caller registers (this is assuming 'entry a1,16') */
+ l32i a4, a1, 0
+ l32i a5, a1, 4
+ s32i a4, a2, 48
+ s32i a5, a2, 52
+ l32i a4, a1, 8
+ l32i a5, a1, 12
+ s32i a4, a2, 56
+ s32i a5, a2, 60
/* Save the return address, including the window size bits. */
s32i a0, a2, 64
- /* a2 still addresses jmp_buf. a15 contains savemask. */
+ /* a2 still points to jmp_buf. a3 contains savemask. */
mov a6, a2
- mov a7, a15
+ mov a7, a3
movi a3, __sigjmp_save
callx4 a3
mov a2, a6