| Message ID | 20230617014930.2070-5-namit@vmware.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: improve debuggability | expand |
On Sat, Jun 17, 2023 at 01:49:28AM +0000, Nadav Amit wrote: > From: Nadav Amit <namit@vmware.com> > > Using gdb for backtracing or dumping the stack following an exception is > not very helpful as the exact location of the exception is not saved. > > Add an additional frame to save the location of the exception. > > One delicate point is dealing with the pretty_print_stacks script. When > the stack is dumped, the script would not print the right address for > the exception address: for every return address it deducts "1" before > looking for the instruction location in the code (using addr2line). As a > somewhat hacky solution add "1" for the exception address when dumping > the stack. > > Signed-off-by: Nadav Amit <namit@vmware.com> > --- > arm/cstart64.S | 13 +++++++++++++ > lib/arm64/asm-offsets.c | 3 ++- > lib/arm64/stack.c | 16 ++++++++++++++++ > 3 files changed, 31 insertions(+), 1 deletion(-) > > diff --git a/arm/cstart64.S b/arm/cstart64.S > index cbd6b51..61e27d3 100644 > --- a/arm/cstart64.S > +++ b/arm/cstart64.S > @@ -314,6 +314,13 @@ exceptions_init: > mrs x2, spsr_el1 > stp x1, x2, [sp, #S_PC] > > + /* > + * Save a frame pointer using the link to allow unwinding of > + * exceptions. > + */ > + stp x29, x1, [sp, #S_FP] > + add x29, sp, #S_FP > + > mov x0, \vec > mov x1, sp > mrs x2, esr_el1 > @@ -349,6 +356,9 @@ exceptions_init: > eret > .endm > > +vector_stub_start: > +.globl vector_stub_start nit: I'd prefer the .globl directives above the labels to match the rest of the file. > + > vector_stub el1t_sync, 0 > vector_stub el1t_irq, 1 > vector_stub el1t_fiq, 2 > @@ -369,6 +379,9 @@ vector_stub el0_irq_32, 13 > vector_stub el0_fiq_32, 14 > vector_stub el0_error_32, 15 > > +vector_stub_end: > +.globl vector_stub_end > + > .section .text.ex > > .macro ventry, label > diff --git a/lib/arm64/asm-offsets.c b/lib/arm64/asm-offsets.c > index 53a1277..7b8bffb 100644 > --- a/lib/arm64/asm-offsets.c > +++ b/lib/arm64/asm-offsets.c > @@ -25,6 +25,7 @@ int main(void) > OFFSET(S_PSTATE, pt_regs, pstate); > OFFSET(S_ORIG_X0, pt_regs, orig_x0); > OFFSET(S_SYSCALLNO, pt_regs, syscallno); > - DEFINE(S_FRAME_SIZE, sizeof(struct pt_regs)); > + DEFINE(S_FRAME_SIZE, (sizeof(struct pt_regs) + 16)); > + DEFINE(S_FP, sizeof(struct pt_regs)); It'd be good to comment this, something like ... OFFSET(S_ORIG_X0, pt_regs, orig_x0); OFFSET(S_SYSCALLNO, pt_regs, syscallno); /* FP and LR (16 bytes) go on the frame above pt_regs */ DEFINE(S_FP, sizeof(struct pt_regs)); DEFINE(S_FRAME_SIZE, (sizeof(struct pt_regs) + 16)); return 0; > return 0; > } > diff --git a/lib/arm64/stack.c b/lib/arm64/stack.c > index 1e2568a..a48ecbb 100644 > --- a/lib/arm64/stack.c > +++ b/lib/arm64/stack.c > @@ -12,6 +12,8 @@ int backtrace_frame(const void *frame, const void **return_addrs, int max_depth) > const void *fp = frame; > void *lr; > int depth; > + bool is_exception = false; > + unsigned long addr; > > /* > * ARM64 stack grows down. fp points to the previous fp on the stack, > @@ -25,6 +27,20 @@ int backtrace_frame(const void *frame, const void **return_addrs, int max_depth) > : ); > > return_addrs[depth] = lr; > + > + /* > + * If this is an exception, add 1 to the pointer so when the > + * pretty_print_stacks script is run it would get the right > + * address (it deducts 1 to find the call address, but we want > + * the actual address). > + */ > + if (is_exception) > + return_addrs[depth] += 1; > + > + /* Check if we are in the exception handlers for the next entry */ > + addr = (unsigned long)lr; > + is_exception = (addr >= (unsigned long)&vector_stub_start && > + addr < (unsigned long)&vector_stub_end); > } > > return depth; > -- > 2.34.1 > Thanks, drew
diff --git a/arm/cstart64.S b/arm/cstart64.S index cbd6b51..61e27d3 100644 --- a/arm/cstart64.S +++ b/arm/cstart64.S @@ -314,6 +314,13 @@ exceptions_init: mrs x2, spsr_el1 stp x1, x2, [sp, #S_PC] + /* + * Save a frame pointer using the link to allow unwinding of + * exceptions. + */ + stp x29, x1, [sp, #S_FP] + add x29, sp, #S_FP + mov x0, \vec mov x1, sp mrs x2, esr_el1 @@ -349,6 +356,9 @@ exceptions_init: eret .endm +vector_stub_start: +.globl vector_stub_start + vector_stub el1t_sync, 0 vector_stub el1t_irq, 1 vector_stub el1t_fiq, 2 @@ -369,6 +379,9 @@ vector_stub el0_irq_32, 13 vector_stub el0_fiq_32, 14 vector_stub el0_error_32, 15 +vector_stub_end: +.globl vector_stub_end + .section .text.ex .macro ventry, label diff --git a/lib/arm64/asm-offsets.c b/lib/arm64/asm-offsets.c index 53a1277..7b8bffb 100644 --- a/lib/arm64/asm-offsets.c +++ b/lib/arm64/asm-offsets.c @@ -25,6 +25,7 @@ int main(void) OFFSET(S_PSTATE, pt_regs, pstate); OFFSET(S_ORIG_X0, pt_regs, orig_x0); OFFSET(S_SYSCALLNO, pt_regs, syscallno); - DEFINE(S_FRAME_SIZE, sizeof(struct pt_regs)); + DEFINE(S_FRAME_SIZE, (sizeof(struct pt_regs) + 16)); + DEFINE(S_FP, sizeof(struct pt_regs)); return 0; } diff --git a/lib/arm64/stack.c b/lib/arm64/stack.c index 1e2568a..a48ecbb 100644 --- a/lib/arm64/stack.c +++ b/lib/arm64/stack.c @@ -12,6 +12,8 @@ int backtrace_frame(const void *frame, const void **return_addrs, int max_depth) const void *fp = frame; void *lr; int depth; + bool is_exception = false; + unsigned long addr; /* * ARM64 stack grows down. fp points to the previous fp on the stack, @@ -25,6 +27,20 @@ int backtrace_frame(const void *frame, const void **return_addrs, int max_depth) : ); return_addrs[depth] = lr; + + /* + * If this is an exception, add 1 to the pointer so when the + * pretty_print_stacks script is run it would get the right + * address (it deducts 1 to find the call address, but we want + * the actual address). + */ + if (is_exception) + return_addrs[depth] += 1; + + /* Check if we are in the exception handlers for the next entry */ + addr = (unsigned long)lr; + is_exception = (addr >= (unsigned long)&vector_stub_start && + addr < (unsigned long)&vector_stub_end); } return depth;