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libgcc: Add a backchain fallback to _Unwind_Backtrace() on PowerPC 

Without dwarf2 unwind tables available _Unwind_Backtrace() is not
able to return the full backtrace.
This patch adds a fallback function on powerpc to get the backtrace
by doing a backchain, this code was originally at glibc.

libgcc/ChangeLog:

	* config/rs6000/linux-unwind.h (struct rt_sigframe): Move it to
	outside of get_regs() in order to use it in another function, this
	is done twice: for __powerpc64__ and for !__powerpc64__.
	(struct trace_arg): New struct.
	(struct layout): New struct.
	(ppc_backchain_fallback): New function.
	* unwind.inc (_Unwind_Backtrace): Look for _URC_NORMAL_STOP code
	state and call MD_BACKCHAIN_FALLBACK.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/unwind-backchain.c: New test.
This commit is contained in:
Raphael Moreira Zinsly 2021-10-05 15:32:52 -03:00 committed by Segher Boessenkool
parent b47490c572
commit b7561b5d24
3 changed files with 124 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
gcc/testsuite/gcc.target/powerpc/unwind-backchain.c Normal file
View File

@ -0,0 +1,24 @@
/* -linux* targets have a fallback for the absence of unwind tables, thus are
the only ones we can guarantee backtrace returns all addresses. */
/* { dg-do run { target { *-*-linux* } } } */
/* { dg-options "-fno-asynchronous-unwind-tables" } */
#include <execinfo.h>
void
test_backtrace()
{
int addresses;
void *buffer[10];
addresses = backtrace(buffer, 10);
if(addresses != 4)
__builtin_abort();
}
int
main()
{
test_backtrace();
return 0;
}

102
libgcc/config/rs6000/linux-unwind.h
View File

@ -94,6 +94,15 @@ struct gcc_ucontext
enum { SIGNAL_FRAMESIZE = 128 };
struct rt_sigframe {
char gap[SIGNAL_FRAMESIZE];
struct gcc_ucontext uc;
unsigned long pad[2];
int tramp[6];
void *pinfo;
struct gcc_ucontext *puc;
};
/* If PC is at a sigreturn trampoline, return a pointer to the
regs. Otherwise return NULL. */
@ -136,14 +145,7 @@ get_regs (struct _Unwind_Context *context)
#endif
{
/* This works for 2.4.21 and later kernels. */
struct rt_sigframe {
char gap[SIGNAL_FRAMESIZE];
struct gcc_ucontext uc;
unsigned long pad[2];
int tramp[6];
void *pinfo;
struct gcc_ucontext *puc;
} *frame = (struct rt_sigframe *) context->cfa;
struct rt_sigframe *frame = (struct rt_sigframe *) context->cfa;
return frame->uc.regs;
}
}
@ -154,6 +156,12 @@ get_regs (struct _Unwind_Context *context)
enum { SIGNAL_FRAMESIZE = 64 };
struct rt_sigframe {
char gap[SIGNAL_FRAMESIZE + 16];
char siginfo[128];
struct gcc_ucontext uc;
};
static struct gcc_regs *
get_regs (struct _Unwind_Context *context)
{
@ -176,11 +184,7 @@ get_regs (struct _Unwind_Context *context)
}
else if (pc[0] == 0x38006666 || pc[0] == 0x380000AC)
{
struct rt_sigframe {
char gap[SIGNAL_FRAMESIZE + 16];
char siginfo[128];
struct gcc_ucontext uc;
} *frame = (struct rt_sigframe *) context->cfa;
struct rt_sigframe *frame = (struct rt_sigframe *) context->cfa;
return frame->uc.regs;
}
return NULL;
@ -203,7 +207,7 @@ ppc_fallback_frame_state (struct _Unwind_Context *context,
int i;
if (regs == NULL)
return _URC_END_OF_STACK;
return _URC_NORMAL_STOP;
new_cfa = regs->gpr[__LIBGCC_STACK_POINTER_REGNUM__];
fs->regs.cfa_how = CFA_REG_OFFSET;
@ -352,3 +356,73 @@ frob_update_context (struct _Unwind_Context *context, _Unwind_FrameState *fs ATT
}
#endif
}
#define MD_BACKCHAIN_FALLBACK ppc_backchain_fallback
struct trace_arg
{
/* Stores the list of addresses. */
void **array;
struct unwind_link *unwind_link;
_Unwind_Word cfa;
/* Number of addresses currently stored. */
int count;
/* Maximum number of addresses. */
int size;
};
/* This is the stack layout we see with every stack frame.
Note that every routine is required by the ABI to lay out the stack
like this.
+----------------+ +-----------------+
%r1 -> | previous frame--------> | previous frame--->... --> NULL
| | | |
| cr save | | cr save |
| | | |
| (unused) | | lr save |
+----------------+ +-----------------+
The CR save is only present on 64-bit ABIs.
*/
struct frame_layout
{
struct frame_layout *backchain;
#ifdef __powerpc64__
long int cr_save;
#endif
void *lr_save;
};
void ppc_backchain_fallback (struct _Unwind_Context *context, void *a)
{
struct frame_layout *current;
struct trace_arg *arg = a;
int count;
/* Get the last address computed and start with the next. */
current = context->cfa;
current = current->backchain;
for (count = arg->count; current != NULL; current = current->backchain)
{
arg->array[count] = current->lr_save;
/* Check if the symbol is the signal trampoline and get the interrupted
symbol address from the trampoline saved area. */
context->ra = current->lr_save;
if (current->lr_save && get_regs (context))
{
struct rt_sigframe *sigframe = (struct rt_sigframe *) current;
if (count + 1 == arg->size)
break;
arg->array[++count] = (void *) sigframe->uc.rsave.nip;
current = (void *) sigframe->uc.rsave.gpr[1];
}
if (count++ >= arg->size)
break;
}
arg->count = count-1;
}

14
libgcc/unwind.inc
View File

@ -300,14 +300,24 @@ _Unwind_Backtrace(_Unwind_Trace_Fn trace, void * trace_argument)
/* Set up fs to describe the FDE for the caller of context. */
code = uw_frame_state_for (&context, &fs);
if (code != _URC_NO_REASON && code != _URC_END_OF_STACK)
if (code != _URC_NO_REASON && code != _URC_END_OF_STACK
&& code != _URC_NORMAL_STOP)
return _URC_FATAL_PHASE1_ERROR;
/* Call trace function. */
if ((*trace) (&context, trace_argument) != _URC_NO_REASON)
return _URC_FATAL_PHASE1_ERROR;
/* We're done at end of stack. */
#ifdef MD_BACKCHAIN_FALLBACK
/* Do a backchain if there is no DWARF data. */
if (code == _URC_NORMAL_STOP)
{
MD_BACKCHAIN_FALLBACK(&context, trace_argument);
break;
}
#endif
/* We're done at end of stack. */
if (code == _URC_END_OF_STACK)
break;