https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=206810
--- Comment #1 from Mark Millard <mar...@dsl-only.net> ---
I tried the following change on/for the powerpc (32-bit) PowerMac that I use
Index: /usr/src/sys/powerpc/powerpc/sigcode32.S
===================================================================
--- /usr/src/sys/powerpc/powerpc/sigcode32.S (revision 294962)
+++ /usr/src/sys/powerpc/powerpc/sigcode32.S (working copy)
@@ -45,9 +45,9 @@
*/
.globl CNAME(sigcode32),CNAME(szsigcode32)
CNAME(sigcode32):
- addi 1,1,-20 /* reserved space for callee */
+ addi 1,1,-32 /* reserved space for callee */
blrl
- addi 3,1,20+SF_UC /* restore sp, and get &frame->sf_uc */
+ addi 3,1,32+SF_UC /* restore sp, and get &frame->sf_uc */
li 0,SYS_sigreturn
sc /* sigreturn(scp) */
li 0,SYS_exit
and the results were:
A) "info frame" in gdb shows signal handlers are now started with 16-byte
aligned stack frames.
and
B) The clang 3.8.0 compiled __vfprintf segmentation faults in libc/stdio
library code during signal handlers no longer happen because the alignment
matches the code requirements.
(Before 2014 it was -16 and 16 instead of -20 and 20, but 16 was too small of a
space. The change to -20 and 20 fixed that but no longer produced aligned stack
frames: It should have gone from -16 and 16 to -32 and 32 to maintain 16 byte
stack alignment while allocating more space.)
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