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http://git.netsurf-browser.org/toolchains.git/commit/?id=cdcd0c5309a9d89a5aea3f7fb82a2d1995d875d9
commit cdcd0c5309a9d89a5aea3f7fb82a2d1995d875d9
Author: John-Mark Bell <[email protected]>
Commit: John-Mark Bell <[email protected]>
arm-riscos-gnueabi: improve stack unwinding
This does require the presence of unwind tables, however.
diff --git a/arm-riscos-gnueabi/recipes/patches/gccsdk/unixlib-unwind.p
b/arm-riscos-gnueabi/recipes/patches/gccsdk/unixlib-unwind.p
new file mode 100644
index 0000000..07290e6
--- /dev/null
+++ b/arm-riscos-gnueabi/recipes/patches/gccsdk/unixlib-unwind.p
@@ -0,0 +1,147 @@
+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
-----------------------------------------------------------------------
Summary of changes:
.../recipes/patches/gccsdk/unixlib-unwind.p | 147 ++++++++++++++++++++
1 file changed, 147 insertions(+)
create mode 100644 arm-riscos-gnueabi/recipes/patches/gccsdk/unixlib-unwind.p
diff --git a/arm-riscos-gnueabi/recipes/patches/gccsdk/unixlib-unwind.p
b/arm-riscos-gnueabi/recipes/patches/gccsdk/unixlib-unwind.p
new file mode 100644
index 0000000..07290e6
--- /dev/null
+++ b/arm-riscos-gnueabi/recipes/patches/gccsdk/unixlib-unwind.p
@@ -0,0 +1,147 @@
+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
--
Cross-compilation toolchains and environments
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