Hi again, I am experimenting with libunwind on a embedded ppc32 system. At the moment I just want to do a native, local unwind using a statically linked demo app. If I compile that test app with the commonly used defaults of -g -O2 I only see main and__libc_start_main. If I specify -g -O0 I get the expected result (correct, deeper back trace).
Ultimately, I want to unwind an application that has been built with optimisation turned up to -O3, so this is a bad result for me just now. Being a little unclear about whether to use libunwind.h/libunwind.a or the -ppc32 suffixed version, I can readily believe I'm doing something wrong. I've opted for the suffixed versions. Is what I am seeing expected behaviour? A colleague tells me that using backtrace_symbols from libc works at -O3. The libc docs suggest that linker options and optimisation can both cause issues. I *think* my use case is "local unwind" and so the call to unw_init_local is appropriate. I recall from earlier that support for ppc32 wasn't headlined in the docs in the way pp64 was; is there a limitation to ppc32 that I'm running into? My configuration of libunwind gave --host=ppc-linux-gnu and CFLAGS of -g -O2. Other options pointed to tools like ppc_82xx-strip etc. Regards, Amit A summary of the outputs is here: // compiled with -O2 linked to libunwind-ppc32.a root@BTNetrix1601437508:/tmp# ./unwinder in bar in foo - call backtrace here 0x10000378: (main+0x10) 0x1000d160: (__libc_start_main+0x178) // compiled with -O0 linked to libunwind-ppc32.a root@BTNetrix1601437508:/tmp# ./unwinder in bar in foo - call backtrace here 0x10000354: (foo+0x28) 0x10000394: (bar+0x28) 0x100003cc: (main+0x20) 0x1000d1c0: (__libc_start_main+0x178) The test app and it's origin are here: // Example app from https://eli.thegreenplace.net \ /2015/programmatic-access-to-the-call-stack-in-c/ #include <libunwind-ppc32.h> // was libunwind.h #include <stdio.h> // Call this function to get a backtrace. void backtrace() { unw_cursor_t cursor; unw_context_t context; // Initialize cursor to current frame for local unwinding. unw_getcontext(&context); unw_init_local(&cursor, &context); // Unwind frames one by one, going up the frame stack. while (unw_step(&cursor) > 0) { unw_word_t offset, pc; unw_get_reg(&cursor, UNW_REG_IP, &pc); if (pc == 0) { break; } printf("0x%lx:", pc); char sym[256]; if (unw_get_proc_name(&cursor, sym, sizeof(sym), &offset) == 0) { printf(" (%s+0x%lx)\n", sym, offset); } else { printf(" -- error: unable to obtain symbol name for this frame\n"); } } } void foo() { printf("in foo - call backtrace here\n"); backtrace(); // <-------- backtrace here! } void bar() { printf("in bar\n"); foo(); } int main(int argc, char **argv) { bar(); return 0; } _______________________________________________ Libunwind-devel mailing list Libunwind-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/libunwind-devel
