riscv64: increase jmp_buf size.
Today's risc-v psABI meeting brought up the topic of CFI-related ABI
changes, and FreeBSD wasn't worried about jmp_buf because they already
had twice the space we do (OpenBSD matches us, presumably because they
too just picked "the next power of two" over what they actually
required), and glibc wasn't worried because they have a hilariously
large sigset_t that they can steal space from (and apparently already
did to support the x86-64 CET shadow stack).
So rather than continue to assume that our minimal amount of free space
will suffice, let's just double it while our ABI isn't yet fixed, and
know we won't have to worry about it in a couple of years time when we
actually have riscv64 hardware shadow stack.
Test: treehugger
Change-Id: I2d4cb2f5db2ac8085a2c9e9ad4f910d0d4792005
diff --git a/libc/include/setjmp.h b/libc/include/setjmp.h
index 6d047ae..0aaaac5 100644
--- a/libc/include/setjmp.h
+++ b/libc/include/setjmp.h
@@ -66,12 +66,14 @@
/**
* The size in words of a riscv64 jmp_buf. Room for callee-saved registers,
* including floating point, stack pointer and program counter, various
- * internal implementation details, and leaving some free space.
+ * internal implementation details, and leaving lots of free space.
*
- * Coincidentally matches OpenBSD, though they also save/restore the
- * floating point status register too.
+ * Deliberately very large given the uncertainty around the final form of
+ * hardware shadow stack, and the fact that x86-64 glibc needed to steal
+ * space from their enormous sigset_t (which we don't have) to be able to
+ * implement the CET shadow stack.
*/
-#define _JBLEN 32
+#define _JBLEN 64
#elif defined(__x86_64__)
/** The size in words of an x86-64 jmp_buf. Inherited from OpenBSD. */
#define _JBLEN 11