Right after DragonFly 4.8 was released (27 Mar 2017), the signal
trampoline was moved (twice) in response to a Ryzen bug. This broke
GCC's unwind support for DragonFly.
To avoid hardcoding the sigtramp location to avoid issues like this in
the future, a new sysctl was added to DragonFly to return the signal
trampoline address range (FreeBSD has a similar sysctl for similar
reasons). The attached patch fixes DragonFly unwind support for current
DragonFly, and maintains support for Release 4.8 and earlier.
This patch has been in use for a few months and works fine. It is
similar in function to the FreeBSD Aarch64 unwind support I submitted
through Andreas T. a few months ago.
I believe the patch can be applied to trunk and release 7 branch.
I am the closest thing to a maintainer for DragonFly, so I don't know if
additional approval is needed. This patch is purely DragonFly-specific
and cannot affect other platforms in any way.
If agreed, it would be great if somebody could commit this for me
against the trunk and GCC-7-branch.
Thanks!
John
P.S. Yes, my copyright assignment is on file (I've contributed a few
patches already).
suggested log entry of libgcc/ChangeLog:
2017-07-XX John Marino <gnu...@marino.st>
* config/i386/dragonfly-unwind.h: Handle sigtramp relocation.
--- libgcc/config/i386/dragonfly-unwind.h.orig 2017-02-06 16:26:52 UTC
+++ libgcc/config/i386/dragonfly-unwind.h
@@ -28,9 +28,13 @@ see the files COPYING3 and COPYING.RUNTI
#include <sys/types.h>
#include <sys/sysctl.h>
+#include <sys/param.h>
#include <signal.h>
#include <sys/ucontext.h>
#include <machine/sigframe.h>
+#if __DragonFly_version > 400800
+#include <sys/kinfo.h>
+#endif
#define REG_NAME(reg) sf_uc.uc_mcontext.mc_## reg
@@ -39,20 +43,44 @@ see the files COPYING3 and COPYING.RUNTI
#define MD_FALLBACK_FRAME_STATE_FOR x86_64_dragonfly_fallback_frame_state
-static void
-x86_64_sigtramp_range (unsigned char **start, unsigned char **end)
+static int
+x86_64_outside_sigtramp_range (unsigned char *pc)
{
- unsigned long ps_strings;
- int mib[2];
- size_t len;
-
- mib[0] = CTL_KERN;
- mib[1] = KERN_PS_STRINGS;
- len = sizeof (ps_strings);
- sysctl (mib, 2, &ps_strings, &len, NULL, 0);
+ static int sigtramp_range_determined = 0;
+ static unsigned char *sigtramp_start, *sigtramp_end;
- *start = (unsigned char *)ps_strings - 32;
- *end = (unsigned char *)ps_strings;
+ if (sigtramp_range_determined == 0)
+ {
+#if __DragonFly_version > 400800
+ struct kinfo_sigtramp kst = {0};
+ size_t len = sizeof (kst);
+ int mib[3] = { CTL_KERN, KERN_PROC, KERN_PROC_SIGTRAMP };
+
+ sigtramp_range_determined = 1;
+ if (sysctl (mib, 3, &kst, &len, NULL, 0) == 0)
+ {
+ sigtramp_range_determined = 2;
+ sigtramp_start = kst.ksigtramp_start;
+ sigtramp_end = kst.ksigtramp_end;
+ }
+#else
+ unsigned long ps_strings;
+ size_t len = sizeof (ps_strings);
+ int mib[2] = { CTL_KERN, KERN_PS_STRINGS };
+
+ sigtramp_range_determined = 1;
+ if (sysctl (mib, 2, &ps_strings, &len, NULL, 0) == 0)
+ {
+ sigtramp_range_determined = 2;
+ sigtramp_start = (unsigned char *)ps_strings - 32;
+ sigtramp_end = (unsigned char *)ps_strings;
+ }
+#endif
+ }
+ if (sigtramp_range_determined < 2) /* sysctl failed if < 2 */
+ return 1;
+
+ return (pc < sigtramp_start || pc >= sigtramp_end );
}
@@ -60,13 +88,10 @@ static _Unwind_Reason_Code
x86_64_dragonfly_fallback_frame_state
(struct _Unwind_Context *context, _Unwind_FrameState *fs)
{
- unsigned char *pc = context->ra;
- unsigned char *sigtramp_start, *sigtramp_end;
struct sigframe *sf;
long new_cfa;
- x86_64_sigtramp_range(&sigtramp_start, &sigtramp_end);
- if (pc >= sigtramp_end || pc < sigtramp_start)
+ if (x86_64_outside_sigtramp_range(context->ra))
return _URC_END_OF_STACK;
sf = (struct sigframe *) context->cfa;
