[Crash-utility] [PATCH] ARM: fix unwinding on recent kernels

[Rabin Vincent]

On Mon, Feb 13, 2012 at 11:59:04AM -0500, Dave Anderson wrote:
> > Maybe add some comment explaining why we do this check (a reference to the
> > kernel commit perhaps)?
> 
> I agree about the comment -- and then some...
> 
> This seems to be a fairly signficant piece of information to be hidden
> in a static variable:
> 
> +static int index_in_prel31;
> 
> Can you put it in the ARM machine_specific data structure?  And then 
> display it in arm_dump_machdep_table() for "help -m".

Here's a v2 of the patch.

Rabin

diff --git a/arm.c b/arm.c
index 4ca2fcd..4be224e 100644
--- a/arm.c
+++ b/arm.c
@@ -406,6 +406,7 @@ arm_dump_machdep_table(ulong arg)
 	fprintf(fp, "exception_text_start: %lx\n", ms->exception_text_start);
 	fprintf(fp, " exception_text_end: %lx\n", ms->exception_text_end);
 	fprintf(fp, "    crash_task_regs: %lx\n", (ulong)ms->crash_task_regs);
+	fprintf(fp, "unwind_index_prel31: %d\n", ms->unwind_index_prel31);
 }
 
 /*
diff --git a/defs.h b/defs.h
index 82d51e5..2e7f6bd 100755
--- a/defs.h
+++ b/defs.h
@@ -4241,6 +4241,7 @@ struct machine_specific {
 	ulong exception_text_start;
 	ulong exception_text_end;
 	struct arm_pt_regs *crash_task_regs;
+	int unwind_index_prel31;
 };
 
 int init_unwind_tables(void);
diff --git a/unwind_arm.c b/unwind_arm.c
index d86ec63..640d6c9 100644
--- a/unwind_arm.c
+++ b/unwind_arm.c
@@ -104,6 +104,7 @@ static int is_core_kernel_text(ulong);
 static struct unwind_table *search_table(ulong);
 static struct unwind_idx *search_index(const struct unwind_table *, ulong);
 static ulong prel31_to_addr(ulong, ulong);
+static void index_prel31_to_addr(struct unwind_table *);
 static int unwind_frame(struct stackframe *, ulong);
 
 /*
@@ -187,6 +188,19 @@ init_kernel_unwind_table(void)
 		goto fail;
 	}
 
+	/*
+	 * Kernel versions before v3.2 (specifically, before commit
+	 * de66a979012db "ARM: 7187/1: fix unwinding for XIP kernels")
+	 * converted the prel31 offsets in the unwind index table to absolute
+	 * addresses on startup.  Newer kernels don't perform this conversion,
+	 * and have a slightly more involved search algorithm.
+	 *
+	 * We always just use the older search method (a straightforward binary
+	 * search) and convert the index table offsets ourselves if we detect
+	 * that the kernel didn't do it.
+	 */
+	machdep->machspec->unwind_index_prel31 = !is_kernel_text(kernel_unwind_table->idx[0].addr);
+
 	kernel_unwind_table->start = kernel_unwind_table->idx;
 	kernel_unwind_table->end = (struct unwind_idx *)
 		((char *)kernel_unwind_table->idx + idx_size);
@@ -194,6 +208,9 @@ init_kernel_unwind_table(void)
 	kernel_unwind_table->end_addr = (kernel_unwind_table->end - 1)->addr;
 	kernel_unwind_table->kv_base = idx_start;
 
+	if (machdep->machspec->unwind_index_prel31)
+		index_prel31_to_addr(kernel_unwind_table);
+
 	if (CRASHDEBUG(1)) {
 		fprintf(fp, "UNWIND: master kernel table start\n");
 		fprintf(fp, "UNWIND: size      : %ld\n", idx_size);
@@ -260,6 +277,9 @@ read_module_unwind_table(struct unwind_table *tbl, ulong addr)
 	tbl->end_addr = TABLE_VALUE(buf, unwind_table_end_addr);
 	tbl->kv_base = idx_start;
 
+	if (machdep->machspec->unwind_index_prel31)
+		index_prel31_to_addr(tbl);
+
 	if (CRASHDEBUG(1)) {
 		fprintf(fp, "UNWIND: module table start\n");
 		fprintf(fp, "UNWIND: start     : %p\n", tbl->start);
@@ -571,6 +591,16 @@ prel31_to_addr(ulong addr, ulong insn)
 	return addr + offset;
 }
 
+static void
+index_prel31_to_addr(struct unwind_table *tbl)
+{
+	struct unwind_idx *idx = tbl->start;
+	ulong kvaddr = tbl->kv_base;
+
+	for (; idx < tbl->end; idx++, kvaddr += sizeof(struct unwind_idx))
+		idx->addr = prel31_to_addr(kvaddr, idx->addr);
+}
+
 static int
 unwind_frame(struct stackframe *frame, ulong stacktop)
 {