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Index: libunixlib/signal/post.c
===================================================================
--- libunixlib/signal/post.c (revision 7698)
+++ libunixlib/signal/post.c (working copy)
@@ -267,9 +267,86 @@
#define FP_OFFSET (-3)
#endif
+#ifdef __ARM_EABI__
+/**
+ * AAPCS does not require the compiler to construct a backtrace structure
+ * in the stack (unlike APCS, which does). This results in FP rarely pointing
+ * at any form of valid stack frame (and, to complicate matters, at the time
+ * of writing, some frames end up with APCS-format frame records, anyway)
+ * which makes it nigh-on impossible to reliably unwind the stack without
+ * additional information). FP is thus often treated as an additional
+ * callee-saved register (i.e. v8) in AAPCS-conformant code.
+ *
+ * Additionally, where frame records are generated, AAPCS has them contain
+ * two entries: previous-FP and LR on entry. There is therefore (unlike APCS)
+ * no way of finding the function entry point from the frame record at all,
+ * even if it did exist.
+ *
+ * So, we cannot trust that FP ever points at a valid stack frame record and
+ * we cannot find function entry points to extract poked function names from.
+ * We can, however, make stack unwinding work if we have some means of
+ * identifying the function in which an arbitrary instruction lies.
+ *
+ * -funwind-tables will result in clang/GCC generating such a data structure,
+ * (an array between __exidx_start and __exidx_end) which will be consulted
+ * by _Unwind_Backtrace() when unwinding the stack.
+ */
+
+#include <unwind.h>
+
+static _Unwind_Reason_Code
+__write_backtrace_cb (_Unwind_Context *ctx, void *pw)
+{
+ _Unwind_Control_Block *ucbp = NULL;
+ const unsigned int *fn;
+
+ ucbp = (_Unwind_Control_Block *) _Unwind_GetGR(ctx, UNWIND_POINTER_REG);
+ fn = (const unsigned int *) ucbp->pr_cache.fnstart;
+
+ fprintf (stderr, " (%8x) fn: %8x pc: %8x sp: %8x ",
+ _Unwind_GetGR (ctx, 11), (unsigned int)fn, _Unwind_GetIP (ctx),
+ _Unwind_GetGR (ctx, 13));
+
+#if PIC
+ /* FIXME: extend this with source location when available. */
+ const char *lib = NULL;
+ unsigned offset;
+ _swix(SOM_Location,
+ _IN(0) | _OUTR(0,1), _Unwind_GetIP (ctx), &lib, &offset);
+ if (lib)
+ fprintf(stderr, " : %8X : %s\n", offset, lib);
+ else
+#endif
+ {
+ int cplusplus_name;
+ const char *name = extract_name (fn, &cplusplus_name);
+ fprintf (stderr, (cplusplus_name) ? " %s\n" : " %s()\n", name);
+ }
+
+ /* TODO: __ul_callback_fp stuff (might need to save/match lr, instead) */
+
+ return _URC_NO_REASON;
+}
+
static void
__write_backtrace_thread (const unsigned int *fp)
{
+ if (fp != NULL)
+ {
+ /* TODO: thread stack traces */
+ fprintf (stderr, "Thread stack traces not supported\n");
+ }
+ else
+ {
+ _Unwind_Backtrace(__write_backtrace_cb, NULL);
+ }
+
+ fputc ('\n', stderr);
+}
+#else
+static void
+__write_backtrace_thread (const unsigned int *fp)
+{
/* Running as USR26 or USR32 ? */
unsigned int is32bit;
__asm__ volatile ("SUBS %[is32bit], r0, r0\n\t" /* Set at least one status flag. */
@@ -306,22 +383,6 @@
break;
}
-#ifdef __ARM_EABI__
- const unsigned int * const lr = (unsigned int *)fp[LR_OFFSET];
- fprintf (stderr, " (%8x) lr: %8x",
- (unsigned int)fp, (unsigned int)lr);
-#if PIC
- /* FIXME: extend this with source location when available. */
- const char *lib = NULL;
- unsigned offset;
- _swix(SOM_Location,
- _IN(0) | _OUTR(0,1), lr, &lib, &offset);
- if (lib)
- fprintf(stderr, " : %8X : %s\n", offset, lib);
- else
-#endif
- fputc('\n', stderr);
-#else
/* Retrieve PC counter.
PC counter has been saved using STMxx ..., { ..., PC } so it can be
8 or 12 bytes away from the STMxx instruction depending on the ARM
@@ -347,10 +408,9 @@
int cplusplus_name;
const char *name = extract_name (pc, &cplusplus_name);
fprintf (stderr, (cplusplus_name) ? " %s\n" : " %s()\n", name);
-#endif
+
oldfp = fp;
fp = (const unsigned int *)fp[FP_OFFSET];
-#ifndef __ARM_EABI__
if (__ul_callbackfp != NULL && fp == __ul_callbackfp)
{
/* At &oldfp[1] = cpsr, a1-a4, v1-v6, sl, fp, ip, sp, lr, pc */
@@ -424,18 +484,17 @@
fputs ("\n\n", stderr);
}
-#endif
}
fputc ('\n', stderr);
}
+#endif
-
void
__write_backtrace (int signo)
{
#ifdef __ARM_EABI__
- register const unsigned int *fp = __builtin_frame_address(0);
+ register const unsigned int *fp = NULL;
#else
register const unsigned int *fp __asm ("fp");
#endif
|
